Annotation of wikisrc/guide/net-practice.mdwn, revision 1.2

1.1       jdf         1: # Setting up TCP/IP on NetBSD in practice
                      3: ## A walk through the kernel configuration
                      5: Before we dive into configuring various aspects of network setup, we want to 
                      6: walk through the necessary bits that have to or can be present in the kernel. 
                      7: See [[Compiling the kernel|guide/kernel]] for more details on compiling the 
                      8: kernel, we will concentrate on the configuration of the kernel here. We will 
                      9: take the i386/GENERIC config file as an example here. Config files for other 
                     10: platforms should contain similar information, the comments in the config files 
                     11: give additional hints. Besides the information given here, each kernel option is 
                     12: also documented in the 
                     13: [options(4)]( 
                     14: manpage, and there is usually a manpage for each driver too, e.g. 
                     15: [tlp(4)](
                     17: The first line of each config file shows the version. It can be used to compare 
                     18: against other versions via CVS, or when reporting bugs.
                     20:     options         NTP             # NTP phase/frequency locked loop
                     22: If you want to run the Network Time Protocol (NTP), this option can be enabled 
                     23: for maximum precision. If the option is not present, NTP will still work. See 
                     24: [ntpd(8)]( for 
                     25: more information.
                     27:     file-system     NFS             # Network File System client
                     29: If you want to use another machine's hard disk via the Network File System 
                     30: (NFS), this option is needed. The guide article about the
                     31: [[Network File System|guide/net-services#nfs]] gives more information on NFS.
                     33:     options         NFSSERVER       # Network File System server
                     35: This option includes the server side of the NFS remote file sharing protocol. 
                     36: Enable if you want to allow other machines to use your hard disk. The mentioned 
                     37: article in the guide about [[NFS|guide/net-services#nfs]] contains more 
                     38: information on NFS.
                     40:     #options        GATEWAY         # packet forwarding
                     42: If you want to setup a router that forwards packets between networks or network 
                     43: interfaces, setting this option is needed. It doesn't only switch on packet 
                     44: forwarding, but also increases some buffers. See 
                     45: [options(4)]( 
                     46: for details.
                     48:     options         INET            # IP + ICMP + TCP + UDP
                     50: This enables the TCP/IP code in the kernel. Even if you don't want/use 
                     51: networking, you will still need this for machine-internal communication of 
                     52: subsystems like the X Window System. See 
                     53: [inet(4)]( for 
                     54: more details.
                     56:     options         INET6           # IPV6
                     58: If you want to use IPv6, this is your option. If you don't want IPv6, which is 
                     59: part of NetBSD since the 1.5 release, you can remove/comment out that option. 
                     60: See the 
                     61: [inet6(4)]( 
                     62: manpage and [[Next generation Internet protocol - 
                     63: IPv6|guide/net-intro#ipv6-intro]] for more information on the next generation 
                     64: Internet protocol.
                     66:     #options        IPSEC           # IP security
                     68: Includes support for the IPsec protocol, including key and policy management, 
                     69: authentication and compression. This option can be used without the previous 
                     70: option INET6, if you just want to use IPsec with IPv4, which is possible. See 
                     71: [ipsec(4)]( for 
                     72: more information.
                     74:     #options        IPSEC_ESP       # IP security (encryption part; define w/IPSEC)
                     76: This option is needed in addition to IPSEC if encryption is wanted in IPsec.
                     78:     #options        MROUTING        # IP multicast routing
                     80: If multicast services like the MBone services should be routed, this option 
                     81: needs to be included. Note that the routing itself is controlled by the 
                     82: [mrouted(8)]( 
                     83: daemon.
                     85:     options         ISO,TPIP        # OSI
                     86:     #options        EON             # OSI tunneling over IP
                     88: These options include the OSI protocol stack, which was said for a long time to 
                     89: be the future of networking. It's mostly history these days. :-) See the 
                     90: [iso(4)]( manpage 
                     91: for more information.
                     93:     options         NETATALK        # AppleTalk networking protocols
                     95: Include support for the AppleTalk protocol stack. Userland server programs are 
                     96: needed to make use of that. See pkgsrc/net/netatalk and pkgsrc/net/netatalk-asun 
                     97: for such packages. More information on the AppleTalk protocol and protocol stack 
                     98: are available in the 
                     99: [atalk(4)]( 
                    100: manpage.
                    102:     options         PPP_BSDCOMP     # BSD-Compress compression support for PPP
                    103:     options         PPP_DEFLATE     # Deflate compression support for PPP
                    104:     options         PPP_FILTER      # Active filter support for PPP (requires bpf)
                    106: These options tune various aspects of the Point-to-Point protocol. The first two 
                    107: determine the compression algorithms used and available, while the third one 
                    108: enables code to filter some packets.
                    110:     options         PFIL_HOOKS      # pfil(9) packet filter hooks
                    111:     options         IPFILTER_LOG    # ipmon(8) log support
                    113: These options enable firewalling in NetBSD, using IPFilter. See the 
                    114: [ipf(4)]( and 
                    115: [ipf(8)]( manpages 
                    116: for more information on operation of IPFilter, and [[Configuring the 
                    117:        gateway/firewall|guide/net-practice#ipnat-configuring-gateway]] for a 
                    118:        configuration example.
                    120:     # Compatibility with 4.2BSD implementation of TCP/IP.  Not recommended.
                    121:     #options        TCP_COMPAT_42
                    123: This option is only needed if you have machines on the network that still run 
                    124: 4.2BSD or a network stack derived from it. If you've got one or more 
                    125: 4.2BSD-systems on your network, you've to pay attention to set the right 
                    126: broadcast-address, as 4.2BSD has a bug in its networking code, concerning the 
                    127: broadcast address. This bug forces you to set all host-bits in the 
                    128: broadcast-address to `0`. The `TCP_COMPAT_42` option helps you ensuring this.
                    130:     options         NFS_BOOT_DHCP,NFS_BOOT_BOOTPARAM
                    132: These options enable lookup of data via DHCP or the BOOTPARAM protocol if the 
                    133: kernel is told to use a NFS root file system. See the 
                    134: [diskless(8)]( 
                    135: manpage for more information.
                    137:     # Kernel root file system and dump configuration.
                    138:     config          netbsd  root on ? type ?
                    139:     #config         netbsd  root on sd0a type ffs
                    140:     #config         netbsd  root on ? type nfs
                    142: These lines tell where the kernel looks for its root file system, and which 
                    143: filesystem type it is expected to have. If you want to make a kernel that uses a 
                    144: NFS root filesystem via the tlp0 interface, you can do this with
                    146:     root on tlp0 type       nfs
                    148: If a `?` is used instead of a device/type, the kernel tries to 
                    149: figure one out on its own.
                    151:     # ISA serial interfaces
                    152:     com0    at isa? port 0x3f8 irq 4        # Standard PC serial ports
                    153:     com1    at isa? port 0x2f8 irq 3
                    154:     com2    at isa? port 0x3e8 irq 5
                    156: If you want to use PPP or SLIP, you will need some serial (com) interfaces. 
                    157: Others with attachment on USB, PCMCIA or PUC will do as well.
                    159:     # Network Interfaces
                    161: This rather long list contains all sorts of network drivers. Please pick the one 
                    162: that matches your hardware, according to the comments. For most drivers, there's 
                    163: also a manual page available, e.g. 
                    164: [tlp(4)](, 
                    165: [ne(4)](, etc.
                    167:     # MII/PHY support
                    169: This section lists media independent interfaces for network cards. Pick one that 
                    170: matches your hardware. If in doubt, enable them all and see what the kernel 
                    171: picks. See the 
                    172: [mii(4)]( manpage 
                    173: for more information.
                    175:     # USB Ethernet adapters
                    176:     aue*    at uhub? port ?         # ADMtek AN986 Pegasus based adapters
                    177:     cue*    at uhub? port ?         # CATC USB-EL1201A based adapters
                    178:     kue*    at uhub? port ?         # Kawasaki LSI KL5KUSB101B based adapters
                    180: USB-ethernet adapters only have about 2MBit/s bandwidth, but they are very 
                    181: convenient to use. Of course this needs other USB related options which we won't 
                    182: cover here, as well as the necessary hardware. See the corresponding manpages 
                    183: for more information.
                    185:     # network pseudo-devices
                    186:     pseudo-device   bpfilter        8       # Berkeley packet filter
                    188: This pseudo-device allows sniffing packets of all sorts. It's needed for 
                    189: tcpdump, but also rarpd and some other applications that need to know about 
                    190: network traffic. See 
                    191: [bpf(4)]( for more 
                    192: information.
                    194:     pseudo-device   ipfilter                # IP filter (firewall) and NAT
                    196: This one enables the IPFilter's packet filtering kernel interface used for 
                    197: firewalling, NAT (IP Masquerading) etc. See 
                    198: [ipf(4)]( and 
                    199: [Configuring the gateway/firewall|guide/net-practice#ipnat-configuring-gateway]] 
                    200: for more information.
                    202:     pseudo-device   loop                    # network loopback
                    204: This is the `lo0` software loopback network device which is used by some 
                    205: programs these days, as well as for routing things. It should not be omitted. 
                    206: See [lo(4)]( for 
                    207: more details.
                    209:     pseudo-device   ppp             2       # Point-to-Point Protocol
                    211: If you want to use PPP either over a serial interface or ethernet (PPPoE), you 
                    212: will need this option. See 
                    213: [ppp(4)]( for 
                    214: details on this interface.
                    216:     pseudo-device   sl              2       # Serial Line IP
                    218: Serial Line IP is a simple encapsulation for IP over (well :) serial lines. It 
                    219: does not include negotiation of IP addresses and other options, which is the 
                    220: reason that it's not in widespread use today any more. See 
                    221: [sl(4)](
                    223:     pseudo-device   strip           2       # Starmode Radio IP (Metricom)
                    225: If you happen to have one of the old Metricom Ricochet packet radio wireless 
                    226: network devices, use this pseudo-device to use it. See the 
                    227: [strip(4)]( 
                    228: manpage for detailed information.
                    230:     pseudo-device   tun             2       # network tunneling over tty
                    232: This network device can be used to tunnel network packets to a device file, 
                    233: `/dev/tun*`. Packets routed to the tun0 interface can be read from `/dev/tun0`, 
                    234: and data written to `/dev/tun0` will be sent out the tun0 network interface. 
                    235: This can be used to implement e.g. QoS routing in userland. See 
                    236: [tun(4)]( for 
                    237: details.
                    239:     pseudo-device   gre             2       # generic L3 over IP tunnel
                    241: The GRE encapsulation can be used to tunnel arbitrary layer 3 packets over IP, 
                    242: e.g. to implement VPNs. See 
                    243: [gre(4)]( for more.
                    245:     pseudo-device   gif             4       # IPv[46] over IPv[46] tunnel (RFC 1933)
                    247: Using the GIF interface allows to tunnel e.g. IPv6 over IPv4, which can be used 
                    248: to get IPv6 connectivity if no IPv6-capable uplink (ISP) is available. Other 
                    249: mixes of operations are possible, too. See the 
                    250: [gif(4)]( manpage 
                    251: for some examples.
                    253:     #pseudo-device  faith           1       # IPv[46] tcp relay translation i/f
                    255: The faith interface captures IPv6 TCP traffic, for implementing userland 
                    256: IPv6-to-IPv4 TCP relays e.g. for protocol transitions. See the 
                    257: [faith(4)]( 
                    258: manpage for more details on this device.
                    260:     #pseudo-device  stf             1       # 6to4 IPv6 over IPv4 encapsulation
                    262: This adds a network device that can be used to tunnel IPv6 over IPv4 without 
                    263: setting up a configured tunnel before. The source address of outgoing packets 
                    264: contains the IPv4 address, which allows routing replies back via IPv4. See the 
                    265: [stf(4)]( manpage 
                    266: and [IPv6 Connectivity & Transition via 6to4|guide/net-practice#ipv6-6to4]] for 
                    267: more details.
                    269:     pseudo-device   vlan                    # IEEE 802.1q encapsulation
                    271: This interface provides support for IEEE 802.1Q Virtual LANs, which allows 
                    272: tagging Ethernet frames with a `vlan` ID. Using properly configured switches 
                    273: (that also have to support VLAN, of course), this can be used to build virtual 
                    274: LANs where one set of machines doesn't see traffic from the other (broadcast and 
                    275: other). The 
                    276: [vlan(4)]( manpage 
                    277: tells more about this.
                    279: ## Overview of the network configuration files
                    281: The following is a list of the files used to configure the network. The usage of 
                    282: these files, some of which have already been met the first chapters, will be 
                    283: described in the following sections.
                    285:  * `/etc/hosts` -- Local hosts database file. Each line contains information 
                    286:    regarding a known host and contains the internet address, the host's name and 
                    287:    the aliases. Small networks can be configured using only the hosts file, 
                    288:    without a *name server*.
                    290:  * `/etc/resolv.conf` -- This file specifies how the routines which provide 
                    291:    access to the Internet Domain Name System should operate. Generally it 
                    292:    contains the addresses of the name servers.
                    294:  * `/etc/` -- This file is used for the automatic configuration of 
                    295:    the network card at boot.
                    297:  * `/etc/mygate` -- Contains the IP address of the gateway.
                    299:  * `/etc/nsswitch.conf` -- Name service switch configuration file. It controls 
                    300:    how a process looks up various databases containing information regarding 
                    301:    hosts, users, groups, etc. Specifically, this file defines the order to look 
                    302:    up the databases. For example, the line:
                    304:        hosts:    files dns
                    306:    specifies that the hosts database comes from two sources, *files* (the local 
                    307:    `/etc/hosts` file) and *DNS*, (the Internet Domain Name System) and that the 
                    308:    local files are searched before the DNS.
                    310:    It is usually not necessary to modify this file.
                    312: ## Connecting to the Internet with a modem
                    314: There are many types of Internet connections: this section explains how to 
                    315: connect to a provider using a modem over a telephone line using the PPP 
                    316: protocol, a very common setup. In order to have a working connection, the 
                    317: following steps must be done:
                    319:  1. Get the necessary information from the provider.
                    320:  2. Edit the file `/etc/resolv.conf` and check `/etc/nsswitch.conf`.
                    321:  3. Create the directories `/etc/ppp` and `/etc/ppp/peers` if they don't exist.
                    322:  4. Create the connection script, the chat file and the pppd options file.
                    323:  5. Created the user-password authentication file.
                    325: Judging from the previous list it looks like a complicated procedure that 
                    326: requires a lot of work. Actually, the single steps are very easy: it's just a 
                    327: matter of modifying, creating or simply checking some small text files. In the 
                    328: following example it will be assumed that the modem is connected to the second 
                    329: serial port `/dev/tty01` (COM2 in DOS).
                    331: A few words on the difference between `com`, `COM` and `tty`. For NetBSD, `com` 
                    332: is the name of the serial port driver (the one that is displayed by `dmesg`) and 
                    333: `tty` is the name of the port. Since numbering starts at 0, `com0` is the driver 
                    334: for the first serial port, named `tty00`. In the DOS world, instead, `COM1` 
                    335: refers to the first serial port (usually located at 0x3f8), `COM2` to the 
                    336: second, and so on. Therefore `COM1` (DOS) corresponds to `/dev/tty00` (NetBSD).
                    338: Besides external modems connected to COM ports (using `/dev/tty0[012]` on i386, 
                    339: `/dev/tty[ab]` on sparc, ...) modems on USB (`/dev/ttyU*`) and pcmcia/cardbus 
                    340: (`/dev/tty0[012]`) can be used.
                    342: ### Getting the connection information
                    344: The first thing to do is ask the provider the necessary information for the 
                    345: connection, which means:
                    347:  * The phone number of the nearest POP.
                    348:  * The authentication method to be used.
                    349:  * The username and password for the connection.
                    350:  * The IP addresses of the name servers.
                    352: ### resolv.conf and nsswitch.conf
                    354: The `/etc/resolv.conf` file must be configured using the information supplied by 
                    355: the provider, especially the addresses of the DNS. In this example the two DNS 
                    356: will be `` and ``:
                    358:     nameserver
                    359:     nameserver
                    361: And now an example of the `/etc/nsswitch.conf` file:
                    363:     # /etc/nsswitch.conf
                    364:     group:         compat
                    365:     group_compat:  nis
                    366:     hosts:         files dns
                    367:     netgroup:      files [notfound=return] nis
                    368:     networks:      files
                    369:     passwd:        compat
                    370:     passwd_compat: nis
                    371:     shells:        files
                    373: The defaults of doing hostname lookups via `/etc/hosts` followed by the DNS 
                    374: works fine and there's usually no need to modify this.
                    376: ### Creating the directories for pppd
                    378: The directories `/etc/ppp` and `/etc/ppp/peers` will contain the configuration 
                    379: files for the PPP connection. After a fresh install of NetBSD they don't exist 
                    380: and must be created (chmod 700).
                    382:     # mkdir /etc/ppp
                    383:     # mkdir /etc/ppp/peers 
                    385: ### Connection script and chat file
                    387: The connection script will be used as a parameter on the pppd command line; it 
                    388: is located in `/etc/ppp/peers` and has usually the name of the provider. For 
                    389: example, if the provider's name is BigNet and your user name for the connection 
                    390: to the provider is alan, an example connection script could be:
                    392:     # /etc/ppp/peers/bignet
                    393:     connect '/usr/sbin/chat -v -f /etc/ppp/peers/'
                    394:     noauth
                    395:     user alan
                    396:     remotename
                    398: In the previous example, the script specifies a *chat file* to be used for the 
                    399: connection. The options in the script are detailed in the 
                    400: [pppd(8)]( man 
                    401: page.
                    403: ### Note
                    405: If you are experiencing connection problems, add the following two lines to the 
                    406: connection script
                    408:     debug
                    409:     kdebug 4
                    411: You will get a log of the operations performed when the system tries to connect. 
                    412: See [pppd(8)](, 
                    413: [syslog.conf(5)](
                    415: The connection script calls the chat application to deal with the physical 
                    416: connection (modem initialization, dialing, ...) The parameters to chat can be 
                    417: specified inline in the connection script, but it is better to put them in a 
                    418: separate file. If, for example, the telephone number of the POP to call is
                    419: `02 99999999`, an example chat script could be:
                    421:     # /etc/ppp/peers/
                    422:     ABORT BUSY
                    423:     ABORT "NO CARRIER"
                    424:     ABORT "NO DIALTONE"
                    425:     '' ATDT0299999999
                    426:     CONNECT ''
                    428: *Note*: If you have problems with the chat file, you can try connecting manually 
                    429: to the POP with the 
                    430: [cu(1)]( program and 
                    431: verify the exact strings that you are receiving.
                    433: ### Authentication
                    435: During authentication each of the two systems verifies the identity of the other 
                    436: system, although in practice you are not supposed to authenticate the provider, 
                    437: but only to be verified by him, using one of the following methods:
                    439:  * PAP/CHAP
                    440:  * login
                    442: Most providers use a PAP/CHAP authentication.
                    444: #### PAP/CHAP authentication
                    446: The authentication information (speak: password) is stored in the 
                    447: `/etc/ppp/pap-secrets` for PAP and in `/etc/ppp/chap-secrets` for CHAP. The 
                    448: lines have the following format:
                    450:     user * password
                    452: For example:
                    454:     alan * pZY9o
                    456: For security reasons the `pap-secrets` and `chap-secrets` files should be owned 
                    457: by root and have permissions 600.
                    459:     # chown root /etc/ppp/pap-secrets
                    460:     # chown root /etc/ppp/chap-secrets
                    461:     # chmod 600 /etc/ppp/pap-secrets
                    462:     # chmod 600 /etc/ppp/chap-secrets
                    464: #### Login authentication
                    466: This type of authentication is not widely used today; if the provider uses login 
                    467: authentication, user name and password must be supplied in the chat file instead 
                    468: of the PAP/CHAP files, because the chat file simulates an interactive login. In 
                    469: this case, set up appropriate permissions for the chat file.
                    471: The following is an example chat file with login authentication:
                    473:     # /etc/ppp/peers/
                    474:     ABORT BUSY
                    475:     ABORT "NO CARRIER"
                    476:     ABORT "NO DIALTONE"
                    477:     '' ATDT0299999999
                    478:     CONNECT ''
                    479:     TIMEOUT 50
                    480:     ogin: alan
                    481:     ssword: pZY9o
                    483: ### pppd options
                    485: The only thing left to do is the creation of the pppd options file, which is 
                    486: `/etc/ppp/options` (chmod 644):
                    488:     /dev/tty01
                    489:     lock
                    490:     crtscts
                    491:     57600
                    492:     modem
                    493:     defaultroute
                    494:     noipdefault
                    496: Check the 
                    497: [pppd(8)]( man 
                    498: page for the meaning of the options.
                    500: ### Testing the modem
                    502: Before activating the link it is a good idea to make a quick modem test, in 
                    503: order to verify that the physical connection and the communication with the 
                    504: modem works. For the test the 
                    505: [cu(1)]( program can 
                    506: be used, as in the following example.
                    508:  1. Create the file `/etc/uucp/port` with the following lines:
                    510:         type modem
                    511:         port modem
                    512:         device /dev/tty01
                    513:         speed 115200
                    515:     (substitute the correct device in place of `/dev/tty01`).
                    517:  2. Write the command `cu -p modem` to start sending commands to the modem. For 
                    518:     example:
                    520:         # cu -p modem
                    521:         Connected.
                    522:         ATZ
                    523:         OK
                    524:         ~.
                    526:         Disconnected.
                    527:         #
                    529:        In the previous example the reset command (ATZ) was sent to the modem, which 
                    530:        replied with OK: the communication works. To exit 
                    531:        [cu(1)](, write 
                    532:        `~` (tilde) followed by `.` (dot), as in the example.
                    534: If the modem doesn't work, check that it is connected to the correct port (i.e. 
                    535: you are using the right port with 
                    536: [cu(1)]( Cables are 
                    537: a frequent cause of trouble, too.
                    539: When you start 
                    540: [cu(1)]( and a 
                    541: message saying `Permission denied` appears, check who is the owner of the 
                    542: `/dev/tty##` device, it must be "uucp". For example:
                    544:     $ ls -l /dev/tty00
                    545:     crw-------  1 uucp  wheel  8, 0 Mar 22 20:39 /dev/tty00
                    547: If the owner is root, the following happens:
                    549:     $ ls -l /dev/tty00
                    550:     crw-------  1 root  wheel  8, 0 Mar 22 20:39 /dev/tty00
                    551:     $ cu -p modem
                    552:     cu: open (/dev/tty00): Permission denied
                    553:     cu: All matching ports in use
                    555: ### Activating the link
                    557: At last everything is ready to connect to the provider with the following 
                    558: command:
                    560:     # pppd call bignet
                    562: where `bignet` is the name of the already described connection script. To see 
                    563: the connection messages of pppd, give the following command:
                    565:     # tail -f /var/log/messages
1.2     ! jdf       567: To disconnect, do a `kill -HUP` of `pppd`.
1.1       jdf       568: 
                    569:      # pkill -HUP pppd 
                    571: ### Using a script for connection and disconnection
                    573: When the connection works correctly, it's time to write a couple of scripts to 
                    574: avoid repeating the commands every time. These two scripts can be named, for 
                    575: example, `ppp-start` and `ppp-stop`.
                    577: `ppp-start` is used to connect to the provider:
                    579:     #!/bin/sh
                    580:     MODEM=tty01
                    581:     POP=bignet
                    582:     if [ -f /var/spool/lock/LCK..$MODEM ]; then
                    583:     echo ppp is already running...
                    584:     else
                    585:     pppd call $POP
                    586:     tail -f /var/log/messages
                    587:     fi
                    589: `ppp-stop` is used to close the connection:
                    591:     #!/bin/sh
                    592:     MODEM=tty01
                    593:     if [ -f /var/spool/lock/LCK..$MODEM ]; then
                    594:     echo -f killing pppd...
                    595:     kill -HUP `cat /var/spool/lock/LCK..$MODEM`
                    596:     echo done
                    597:     else
                    598:     echo ppp is not active
                    599:     fi
                    601: The two scripts take advantage of the fact that when pppd is active, it creates 
                    602: the file `LCK..tty01` in the `/var/spool/lock` directory. This file contains the 
                    603: process ID (*pid*) of the pppd process.
                    605: The two scripts must be executable:
                    607:     # chmod u+x ppp-start ppp-stop
                    609: ### Running commands after dialin
                    611: If you find yourself to always run the same set of commands each time you dial 
                    612: in, you can put them in a script `/etc/ppp/ip-up` which will be called by 
                    613: [pppd(8)]( after 
                    614: successful dial-in. Likewise, before the connection is closed down, 
                    615: `/etc/ppp/ip-down` is executed. Both scripts are expected to be executable. See 
                    616: [pppd(8)]( for 
                    617: more details.
                    619: ## Creating a small home network
                    621: Networking is one of the main strengths of Unix and NetBSD is no exception: 
                    622: networking is both powerful and easy to set up and inexpensive too, because 
                    623: there is no need to buy additional software to communicate or to build a server. 
                    624: [[Setting up an Internet gateway with IPNAT|guide/net-practice#ipnat]] explains 
                    625: how to configure a NetBSD machine to act as a gateway for a network: with IPNAT 
                    626: all the hosts of the network can reach the Internet with a single connection to 
                    627: a provider made by the gateway machine. The only thing to be checked before 
                    628: creating the network is to buy network cards supported by NetBSD (check the 
                    629: `INSTALL.*` files for a list of supported devices).
                    631: First, the network cards must be installed and connected to a hub, switch or 
                    632: directly (see the next image for an example configuration).
                    634: Next, check that the network cards are recognized by the kernel, studying the 
                    635: output of the `dmesg` command. In the following example the kernel recognized 
                    636: correctly an NE2000 clone:
                    638:     ...
                    639:     ne0 at isa0 port 0x280-0x29f irq 9
                    640:     ne0: NE2000 Ethernet
                    641:     ne0: Ethernet address 00:c2:dd:c1:d1:21
                    642:     ...
                    644: If the card is not recognized by the kernel, check that it is enabled in the 
                    645: kernel configuration file and then that the card's IRQ matches the one that the 
                    646: kernel expects. For example, this is the isa NE2000 line in the configuration 
                    647: file; the kernel expects the card to be at IRQ 9.
                    649:     ...
                    650:     ne0 at isa? port 0x280 irq 9 # NE[12]000 ethernet cards
                    651:     ...
                    653: If the card's configuration is different, it will probably not be found at boot. 
                    654: In this case, either change the line in the kernel configuration file and 
                    655: compile a new kernel or change the card's setup (usually through a setup disk 
                    656: or, for old cards, a jumper on the card).
                    658: The following command shows the network card's current configuration:
                    660:     # ifconfig ne0
                    661:     ne0: flags=8822<BROADCAST,NOTRAILERS,SIMPLEX,MULTICAST> mtu 1500
                    662:     address: 00:50:ba:aa:a7:7f
                    663:     media: Ethernet autoselect (10baseT)
                    664:     inet6 fe80::250:baff:feaa:a77f%ne0 prefixlen 64 scopeid 0x1 
                    666: The software configuration of the network card is very easy. The IP address 
                    667: is assigned to the card.
                    669:     # ifconfig ne0 inet netmask 0xffffff00
                    671: Note that the networks and are reserved for private 
                    672: networks, which is what we're setting up here.
                    674: Repeating the previous command now gives a different result:
                    676:     # ifconfig ne0
                    677:     ne0: flags=8863<UP,BROADCAST,NOTRAILERS,RUNNING,SIMPLEX,MULTICAST> mtu 1500
                    678:     address: 00:50:ba:aa:a7:7f
                    679:     media: Ethernet autoselect (10baseT)
                    680:     inet netmask 0xffffff00 broadcast
                    681:     inet6 fe80::250:baff:feaa:a77f%ne0 prefixlen 64 scopeid 0x1 
                    683: The output of `ifconfig` has now changed: the IP address is now printed and 
                    684: there are two new flags, `UP` and `RUNNING` If the interface isn't `UP`, it will 
                    685: not be used by the system to send packets.
                    687: The host was given the IP address, which belongs to the set of 
                    688: addresses reserved for internal networks which are not reachable from the 
                    689: Internet. The configuration is finished and must now be tested; if there is 
                    690: another active host on the network, a `ping` can be tried. For example, if 
                    691: is the address of the active host:
                    693:     # ping
                    694:     PING ape ( 56 data bytes
                    695:     64 bytes from icmp_seq=0 ttl=255 time=1.286 ms
                    696:     64 bytes from icmp_seq=1 ttl=255 time=0.649 ms
                    697:     64 bytes from icmp_seq=2 ttl=255 time=0.681 ms
                    698:     64 bytes from icmp_seq=3 ttl=255 time=0.656 ms
                    699:     ^C
                    700:     ----ape PING Statistics----
                    701:     4 packets transmitted, 4 packets received, 0.0% packet loss
                    702:     round-trip min/avg/max/stddev = 0.649/0.818/1.286/0.312 ms
                    704: With the current setup, at the next boot it will be necessary to repeat the 
                    705: configuration of the network card. In order to avoid repeating the card's 
                    706: configuration at each boot, add the following lines to `/etc/rc.conf`:
                    708:     auto_ifconfig=yes
                    709:     ifconfig_ne0="inet netmask 0xffffff00" 
                    711: In this example the variable `ifconfig_ne0` was set because the network card was 
                    712: recognized as *ne0* by the kernel; if you are using a different adapter, 
                    713: substitute the appropriate name in place of ne0.
                    715: At the next boot the network card will be configured automatically.
                    717: If you have a router that is connected to the internet, you can use it as 
                    718: default router, which will handle all your packets. To do so, set `defaultroute` 
                    719: to the router's IP address in `/etc/rc.conf`:
                    721:     defaultroute=
                    723: Be sure to use the default router's IP address instead of name, in case your DNS 
                    724: server is beyond the default router. In that case, the DNS server couldn't be 
                    725: reached to resolve the default router's hostname and vice versa, creating a 
                    726: chicken-and-egg problem.
                    728: To reach hosts on your local network, and assuming you really have very few 
                    729: hosts, adjust `/etc/hosts` to contain the addresses of all the hosts belonging 
                    730: to the internal network. For example:
                    732:     #
                    733:     # Host Database
                    734:     # This file should contain the addresses and aliases
                    735:     # for local hosts that share this file.
                    736:     # It is used only for "ifconfig" and other operations
                    737:     # before the nameserver is started.
                    738:     #
                    739:     #
                    740:             localhost
                    741:     ::1                   localhost
                    742:     #
                    743:     # RFC 1918 specifies that these networks are "internal".
                    744:     #
                    745:     #
                    746:     #
                    748: ape
                    749: vespa
                    752: If you are dialed in via an Internet Service Provider, or if you have a local 
                    753: Domain Name Server (DNS) running, you may want to use it to resolve hostnames to 
                    754: IP addresses, possibly in addition to `/etc/hosts`, which would only know your 
                    755: own hosts. To configure a machine as DNS client, you need to edit 
                    756: `/etc/resolv.conf`, and enter the DNS server's address, in addition to an 
                    757: optional domain name that will be appended to hosts with no domain, in order to 
                    758: create a FQDN for resolving. Assuming your DNS server's IP address is 
                    759: and it is setup to serve for "", put the following into 
                    760: `/etc/resolv.conf`:
                    762:     # /etc/resolv.conf
                    763:     domain
                    764:     nameserver
                    766: The `/etc/nsswitch.conf` file should be checked as explained in the previous 
                    767: [[nsswitch.conf example|guide/net-practice#rc.conf_and_nsswitch.conf]].
                    769: Summing up, to configure the network the following must be done: the network 
                    770: adapters must be installed and physically connected. Next they must be 
1.2     ! jdf       771: configured (with `ifconfig`) and, finally, the file `/etc/rc.conf` must be 
1.1       jdf       772: modified to configure the interface and possibly default router, and 
                    773: `/etc/resolv.conf` and `/etc/nsswitch.conf` should be adjusted if DNS should be 
                    774: used. This type of network management is sufficient for small networks without 
                    775: sophisticated needs.
                    777: ## Setting up an Internet gateway with IPNAT
                    779: The mysterious acronym IPNAT hides the Internet Protocol Network Address 
                    780: Translation, which enables the routing of an internal network (e.g. your home 
                    781: network as described in the previous section) on a real network (Internet). This 
                    782: means that with only one *real* IP, static or dynamic, belonging to a gateway 
                    783: running IPNAT, it is possible to create simultaneous connections to the Internet 
                    784: for all the hosts of the internal network.
                    786: Some usage examples of IPNAT can be found in the subdirectory 
                    787: `/usr/share/examples/ipf`: look at the files `BASIC.NAT` and `nat-setup`.
                    789: The setup for the example described in this section is detailed in the following 
                    790: figure: *host 1* can connect to the Internet calling a provider with a modem and 
                    791: getting a dynamic IP address. *host 2* and *host 3* can't communicate with the 
                    792: Internet with a normal setup: IPNAT allows them to do it: host 1 will act as a 
                    793: Internet gateway for hosts 2 and 3. Using host 1 as default router, hosts 2 and 
                    794: 3 will be able to access the Internet.
                    796: ![Network with gateway](/guide/images/net1.gif)  
                    797: **Network with gateway**
                    799: ### Configuring the gateway/firewall
                    801: To use IPNAT, the *pseudo-device ipfilter* must be compiled into the kernel, and 
                    802: IP packet forwarding must be enabled in the kernel. To check, run:
                    804:     # sysctl net.inet.ip.forwarding
                    805:     net.inet.ip.forwarding = 1
                    807: If the result is `1` as in the previous example, the option is enabled, 
                    808: otherwise, if the result is `0` the option is disabled. You can do two things:
                    810:  1. Compile a new kernel, with the GATEWAY option enabled.
                    812:  2. Enable the option in the current kernel with the following command:
                    814:         # sysctl -w net.inet.ip.forwarding=1
                    816:        You can add sysctl settings to `/etc/sysctl.conf` to have them set 
                    817:        automatically at boot. In this case you would want to add
                    819:         net.inet.ip.forwarding=1
                    822: The rest of this section explains how to create an IPNAT configuration that is 
                    823: automatically started every time that a connection to the provider is activated 
                    824: with the PPP link. With this configuration all the host of a home network (for 
                    825: example) will be able to connect to the Internet through the gateway machine, 
                    826: even if they don't use NetBSD.
                    828: For the setup, first, create the `/etc/ipnat.conf` file containing the following 
                    829: rules:
                    831:     map ppp0 -> 0/32 proxy port ftp ftp/tcp
                    832:     map ppp0 -> 0/32 portmap tcp/udp 40000:60000
                    833:     map ppp0 -> 0/32
                    835: are the network addresses that should be mapped. The first line 
                    836: of the configuration file is optional: it enables active FTP to work through the 
                    837: gateway. The second line is used to handle correctly tcp and udp packets; the 
                    838: portmapping is necessary because of the many to one relationship). The third 
                    839: line is used to enable ICMP, ping, etc.
                    841: Next, create the `/etc/ppp/ip-up` file; it will be called automatically every 
                    842: time that the PPP link is activated:
                    844:     #!/bin/sh
                    845:     # /etc/ppp/ip-up
                    846:     /etc/rc.d/ipnat forcestart
                    848: Create the file `/etc/ppp/ip-down`; it will be called automatically when the PPP 
                    849: link is closed:
                    851:     #!/bin/sh
                    852:     # /etc/ppp/ip-down
                    853:     /etc/rc.d/ipnat forcestop
                    855: Both `ip-up` and `ip-down` must be executable:
                    857:     # chmod u+x ip-up ip-down
                    859: The gateway machine is now ready.
                    861: ### Configuring the clients
                    863: Create a `/etc/resolv.conf` file like the one on the gateway machine, to make 
                    864: the clients access the same DNS server as the gateway.
                    866: Next, make all clients use the gateway as their default router. Use the 
                    867: following command:
                    869:     # route add default
                    871: is the address of the gateway machine configured in the previous 
                    872: section.
                    874: Of course you don't want to give this command every time, so it's better to 
                    875: define the `defaultroute` entry in the `/etc/rc.conf` file: the default route 
                    876: will be set automatically during system initialization, using the defaultroute 
1.2     ! jdf       877: option as an argument to the `route add default` command.
1.1       jdf       878: 
                    879: If the client machine is not using NetBSD, the configuration will be different. 
                    880: On Windows PCs you need to set the gateway property of the TCP/IP protocol to 
                    881: the IP address of the NetBSD gateway.
                    883: That's all that needs to be done on the client machines.
                    885: ### Some useful commands
                    887: The following commands can be useful for diagnosing problems:
                    889:  * `ping` -- tries to connect to other computers via ICMP (usually used for 
                    890:    testing if a connection exists).
1.2     ! jdf       891:  * `netstat -r` -- Displays the routing tables (similar to `route show`).
1.1       jdf       892:  * `traceroute` -- On the client it shows the route followed by the packets to 
                    893:    their destination.
                    894:  * `tcpdump` -- Use on the gateway to monitor TCP/IP traffic.
                    896: ## Setting up a network bridge device
                    898: A bridge can be used to combine different physical networks into one logical 
                    899: network, i.e. connect them at layer 2 of the ISO-OSI model, not at layer 3, 
                    900: which is what a router would do. The NetBSD `bridge` driver provides bridge 
                    901: functionality on NetBSD systems.
                    903: ### Bridge example
                    905: In this example two physical networks are going to be combined in one logical 
                    906: network,, using a NetBSD bridge. The NetBSD machine which is going 
                    907: to act as bridge has two interfaces, ne0 and ne1, which are each connected to 
                    908: one physical network.
                    910: The first step is to make sure support for the `bridge` is compiled in the 
                    911: running kernel. Support is included in the GENERIC kernel.
                    913: When the system is ready the bridge can be created, this can be done using the 
                    914: [brconfig(8)]((
                    915: command. First of a bridge interface has to be created. With the following 
                    916: `ifconfig` command the `bridge0` interface will be created:
                    918:     $ ifconfig bridge0 create
                    920: Please make sure that at this point both the ne0 and ne1 interfaces are up. The 
                    921: next step is to add the ne0 and ne1 interfaces to the bridge.
                    923:     $ brconfig bridge0 add ne0 add ne1 up
                    925: This configuration can be automatically set up by creating an 
                    926: `/etc/ifconfig.interface` file, in this case `/etc/ifconfig.bridge0`, with the 
                    927: following contents:
                    929:     create
                    930:             !brconfig $int add ne0 add ne1 up
                    932: After setting up the bridge the bridge configuration can be displayed using the 
                    933: `brconfig -a` command. Remember that if you want to give the bridge machine an 
                    934: IP address you can only allocate an IP address to one of the interfaces which 
                    935: are part of the bridge.
                    937: ## A common LAN setup
                    939: The small home network discussed in the previous section contained many items 
                    940: that were configured manually. In bigger LANs that are centrally managed, one 
                    941: can expect Internet connectivity being available via some router, a DNS server 
                    942: being available, and most important, a DHCP server which hands out IP addresses 
                    943: to clients on request. To make a NetBSD client run in such an environment, it's 
                    944: usually enough to set
                    946:     dhclient=yes
                    948: in `/etc/rc.conf`, and the IP address will be set automatically, 
                    949: `/etc/resolv.conf` will be created and routing setup to the default router.
                    951: ## Connecting two PCs through a serial line
                    953: If you need to transfer files between two PCs which are not networked there is a 
                    954: simple solution which is particularly handy when copying the files to a floppy 
                    955: is not practical: the two machines can be networked with a serial cable (a *null 
                    956: modem* cable). The following sections describe some configurations.
                    958: ### Connecting NetBSD with BSD or Linux
                    960: The easiest case is when both machines run NetBSD: making a connection with the 
                    961: SLIP protocol is very easy. On the first machine write the following commands:
                    963:     # slattach /dev/tty00
                    964:     # ifconfig sl0 inet
                    966: On the second machine write the following commands:
                    968:     # slattach /dev/tty00
                    969:     # ifconfig sl0 inet
                    971: Now you can test the connection with `ping`; for example, on the second PC 
                    972: write:
                    974:     # ping
                    976: If everything worked there is now an active network connection between the two 
                    977: machines and ftp, telnet and other similar commands can be executed. The textual 
                    978: aliases of the machines can be written in the `/etc/hosts` file.
                    980:  * In the previous example both PCs used the first serial port (`/dev/tty0`). 
                    981:    Substitute the appropriate device if you are using another port.
                    983:  * IP addresses like 192.168.x.x are reserved for `internal` networks. The first 
                    984:    PC has address and the second
                    986:  * To achieve a faster connection the `-s speed` option to `slattach` can be 
                    987:    specified.
                    989:  * `ftp` can be used to transfer files only if inetd is active and the ftpd 
                    990:  * server is enabled.
                    992: ### Linux
                    994: If one of the two PCs runs Linux, the commands are slightly different (on the 
                    995: Linux machine only). If the Linux machine gets the address, the 
                    996: following commands are needed:
                    998:     # slattach -p slip -s 115200 /dev/ttyS0 &
                    999:     # ifconfig sl0 pointopoint up
                   1000:     # route add dev sl0
                   1002: Don't forget the `&` in the first command.
                   1004: ### Connecting NetBSD and Windows NT
                   1006: NetBSD and Windows NT can be (almost) easily networked with a serial *null 
                   1007: modem* cable. Basically what needs to be done is to create a *Remote Access* 
                   1008: connection under Windows NT and to start pppd on NetBSD.
                   1010: Start pppd as root after having created a `.ppprc` in `/root`. Use the following 
                   1011: example as a template.
                   1013:     connect '/usr/sbin/chat -v CLIENT CLIENTSERVER'
                   1014:     local
                   1015:     tty00
                   1016:     115200
                   1017:     crtscts
                   1018:     lock
                   1019:     noauth
                   1020:     nodefaultroute
                   1021:     :
                   1023: The meaning of the first line will be explained later in this section; 
                   1024: is the IP address that will be assigned by NetBSD to the Windows NT 
                   1025: host; `tty00` is the serial port used for the connection (first serial port).
                   1027: On the NT side a *null modem* device must be installed from the Control Panel 
                   1028: (Modem icon) and a Remote Access connection using this modem must be created. 
                   1029: The null modem driver is standard under Windows NT 4 but it's not a 100% null 
                   1030: modem: when the link is activated, NT sends the string CLIENT and expects to 
                   1031: receive the answer CLIENTSERVER. This is the meaning of the first line of the 
                   1032: `.ppprc` file: `chat` must answer to NT when the connection is activated or 
                   1033: the connection will fail.
                   1035: In the configuration of the Remote Access connection the following must be 
                   1036: specified: use the null modem, telephone number `1` (it's not used, anyway), PPP 
                   1037: server, enable only TCP/IP protocol, use IP address and nameservers from the 
                   1038: server (NetBSD in this case). Select the hardware control flow and set the port 
                   1039: to 115200 8N1.
                   1041: Now everything is ready to activate the connection.
                   1043:  * Connect the serial ports of the two machines with the null modem cable.
                   1044:  * Launch pppd on NetBSD. To see the messages of pppd:
                   1045:    `tail -f /var/log/messages`).
                   1046:  * Activate the Remote Access connection on Windows NT.
                   1048: ### Connecting NetBSD and Windows 95
                   1050: The setup for Windows 95 is similar to the one for Windows NT: Remote Access on 
                   1051: Windows 95 and the PPP server on NetBSD will be used. Most (if not all) Windows 
                   1052: 95 releases don't have the *null modem* driver, which makes things a little more 
                   1053: complicated. The easiest solution is to find one of the available null modem 
                   1054: drivers on the Internet (it's a small `.INF` file) and repeat the same steps as 
                   1055: for Windows NT. The only difference is that the first line of the `.ppprc` file 
                   1056: (the one that calls `chat`) can be removed.
                   1058: If you can't find a real null modem driver for Windows 95 it's still possible to 
                   1059: use a little trick:
                   1061:  * Create a Remote Access connection like the one described before for Windows 
                   1062:    NT, but using the *Standard Modem*.
1.2     ! jdf      1064:  * In `.ppprc` substitute the line that calls `chat` with the following line
1.1       jdf      1065: 
                   1066:        connect '/usr/sbin/chat -v ATH OK AT OK ATE0V1 OK AT OK ATDT CONNECT'
                   1068:  * Activate the connection as described in the section before for Windows NT.
                   1071: In this way the `chat` program, called when the connection is activated, 
                   1072: emulates what Windows 95 thinks is a standard modem, returning to Windows 95 the 
                   1073: same answers that a standard modem would return. Whenever Windows 95 sends a 
                   1074: modem command string, `chat` returns OK.
                   1076: ## IPv6 Connectivity & Transition via 6to4
                   1078: This section will concentrate on how to get network connectivity for IPv6 and - 
                   1079: as that is rarely available directly - talk at length about the alternatives to 
                   1080: native IPv6 connectivity as a transitional method until native IPv6 peers are 
                   1081: available.
                   1083: Finding an ISP that offers IPv6 natively needs quite some luck. What you need 
                   1084: next is a router that will be able to handle the traffic. To date, not all 
                   1085: router manufacturers offer IPv6 or hardware accelerated IPv6 features, and 
                   1086: gateway NAT boxes only rarely support IPv6 and also block IPv6 tunnels. An 
                   1087: alternative approach involves configuring a standard PC running NetBSD to act as 
                   1088: a router. The base NetBSD system contains a complete IPv6 routing solution, and 
                   1089: for special routing needs software like Zebra can provide additional routing 
                   1090: protocols. This solution is rather common for sites that want IPv6 
                   1091: connectivity today. The drawbacks are that you need an ISP that supports 
                   1092: IPv6 and that you may need a dedicated uplink only for IPv6.
                   1094: IPv6 to-the-door may be rare, but you can still get IPv6 connectivity by using 
                   1095: tunnels. Instead of talking IPv6 on the wire, the IPv6 packets are encapsulated 
                   1096: in IPv4 packets, as shown in the next image. Using the existing IPv4 
                   1097: infrastructure, the encapsulated packets are sent to a IPv6-capable uplink that 
                   1098: will then remove the encapsulation, and forward the IPv6 packets.
                   1100: ![A frequently used method for transition is tunneling IPv6 in IPv4 packets](/guide/images/ipv6-en-2tunnel.gif)  
                   1101: **A frequently used method for transition is tunneling IPv6 in IPv4 packets**
                   1103: When using tunnels, there are two possibilities. One is to use a so-called 
                   1104: *configured* tunnel, the other is called an *automatic* tunnel. A *configured* 
                   1105: tunnel is one that required preparation from both ends of the tunnel, usually 
                   1106: connected with some kind of registration to exchange setup information. An 
                   1107: example for such a configured tunnel is the IPv6-over-IPv4 encapsulation 
                   1108: described in
                   1109: [RFC1933]( ("RFC 1933: Transition Mechanisms 
                   1110: for IPv6 Hosts and Routers"), and that's implemented e.g. by the 
                   1111: [gif(4)]( 
                   1112: device found in NetBSD.
                   1114: An *automatic* tunnel consists of a public server that has some kind of IPv6 
                   1115: connectivity, e.g. via 6Bone. That server has made its connectivity data public, 
                   1116: and also runs a tunneling protocol that does not require an explicit 
                   1117: registration of the sites using it as uplink. A well-used example of such a 
                   1118: protocol is the 6to4 mechanism described in
                   1119: [RFC3056]( ("RFC 3056: Connection of IPv6 
                   1120: Domains via IPv4 Clouds"), and that is implemented in the 
                   1121: [stf(4)]( device 
                   1122: found in NetBSD's. Another mechanism that does not require registration of 
                   1123: IPv6-information is the 6over4 mechanism, which implements transporting of IPv6 
                   1124: over a multicast-enabled IPv4 network, instead of e.g. ethernet or FDDI.  6over4 
                   1125: is documented in [RFC2529]( ("RFC 2529: 
                   1126: Transmission of IPv6 over IPv4 Domains without Explicit Tunnels"). It's main 
                   1127: drawback is that you do need existing multicast infrastructure. If you don't 
                   1128: have that, setting it up is about as much effort as setting up a configured IPv6 
                   1129: tunnel directly, so it's usually not worth bothering in that case.
                   1131: ### Getting 6to4 IPv6 up & running
                   1133: 6to4 is an easy way to get IPv6 connectivity for hosts that only have an IPv4 
                   1134: uplink, especially if you have the background given in
                   1135: [[the chapter about IPv6|guide/net-intro#ipv6-intro]]. It can be used with 
                   1136: static as well as dynamically assigned IPv4 addresses, e.g. as found in modem 
                   1137: dialup scenarios today. When using dynamic IPv4 addresses, a change of IP 
                   1138: addresses will be a problem for incoming traffic, i.e. you can't run persistent 
                   1139: servers.
                   1141: Example configurations given in this section are for NetBSD 1.5.2.
                   1143: ### Obtaining IPv6 Address Space for 6to4
                   1145: The 6to4 IPv6 setup on your side doesn't consist of a single IPv6 address; 
                   1146: Instead, you get a whole /48 network! The IPv6 addresses are derived from your 
                   1147: (single) IPv4 address. The address prefix *2002:` is reserved for 6to4 based 
                   1148: addresses (i.e. IPv6 addresses derived from IPv4 addresses). The next 32 bits 
                   1149: are your IPv4 address. This results in a /48 network that you can use for your 
                   1150: very own purpose. It leaves 16 bits space for 2^16^ IPv6 subnets, which can take 
                   1151: up to 2^64^ nodes each. The next figure illustrates the building of your IPv6 
                   1152: address (range) from your IPv4 address.
                   1154: Thanks to the 6to4 prefix and your worldwide unique IPv4 address, this address 
                   1155: block is unique, and it's mapped to your machine carrying the IPv4 address in 
                   1156: question.
                   1158: ![6to4 derives an IPv6 from an IPv4 address](/guide/images/ipv6-en-3adr.gif)  
                   1159: **6to4 derives an IPv6 from an IPv4 address**
                   1161: ### How to get connected
                   1163: In contrast to the configured *IPv6-over-IPv4 tunnel* setup, you do not have to 
                   1164: register at a 6bone-gateway, which would only then forward your IPv6 traffic 
                   1165: encapsulated in IPv4. Instead, as your IPv6 address is derived from your IPv4 
                   1166: address, inbound traffic can be sent through the nearest 6to4 relay router. 
                   1167: De-encapsulation of the packet is done via a 6to4-capable network interface, 
                   1168: which then forwards the resulting IPv6 packet according to your routing setup 
                   1169: (in case you have more than one machine connected on your 6to4 assigned 
                   1170: network).
                   1172: To transmit IPv6 packets, the 6to4 router will encapsulate them inside IPv4 
                   1173: packets; a system performing these functions is called a 6to4 border router. 
                   1174: These packets have a default route to the *6to4 relay anycast prefix*. This 
                   1175: anycast prefix will route the tunnel to a *6to4 relay router*.
                   1177: ![Request and reply can be routed via different gateways in 6to4](/guide/images/ipv6-en-1scene.gif)  
                   1178: **Request and reply can be routed via different gateways in 6to4**
                   1180: ### Security Considerations
                   1182: In contrast to the *configured tunnel* setup, you usually can't setup packet 
                   1183: filters to block 6to4-packets from unauthorized sources, as this is exactly how 
                   1184: (and why) 6to4 works at all. As such, malicious users can send packets with 
                   1185: invalid/hazardous IPv6 payload. If you don't already filter on your border 
                   1186: gateways anyways, packets with the following characteristics should not be 
                   1187: allowed as valid 6to4 packets, and some firewalling seems to be justified for 
                   1188: them:
                   1190:  * unspecified IPv4 source/destination address:
                   1191:  * loopback address in outer (v4) source/destination:
                   1192:  * IPv4 multicast in source/destination:
                   1193:  * limited broadcasts:
                   1194:  * subnet broadcast address as source/destination: depends on your IPv4 setup
                   1196: The NetBSD 
                   1197: [stf(4)]( manual 
                   1198: page documents some common configuration mistakes intercepted by default by the 
                   1199: KAME stack as well as some further advice on filtering, but keep in mind that 
                   1200: because of the requirement of these filters, 6to4 is not perfectly secure. 
                   1201: Still, if forged 6to4 packets become a problem, you can use IPsec authentication 
                   1202: to ensure the IPv6 packets are not modified.
                   1204: ### Data Needed for 6to4 Setup
                   1206: In order to setup and configure IPv6 over 6to4, a few bits of configuration data 
                   1207: must be known in advance. These are:
                   1209:  * Your local IPv4 address. It can be determined using either the `ifconfig -a` 
                   1210:    or `netstat -i` commands on most Unix systems. If you use a NATing gateway or 
                   1211:    something, be sure to use the official, outside-visible address, not your 
                   1212:    private (10/8 or 192.168/16) one.
                   1214:    We will use as the local IPv4 address in our example.
                   1216:  * Your local IPv6 address, as derived from the IPv4 address. See the previous 
                   1217:    figure ("6to4 derives an IPv6 from an IPv4 address") about how to do so.
                   1219:    For our example, this is 2002:3ee0:3972:0001::1 ( == 0x3ee03972, 
                   1220:    0001::1 arbitrarily chosen).
                   1222:  * The *6to4 IPv6 relay anycast address*. which is 2002:c058:6301::, or the IPv6 
                   1223:    address of a specific 6to4 relay router you want to use. The IPv6 address 
                   1224:    will do, as it also contains the IPv4 address in the usual 6to4 translation.
                   1226: ### Kernel Preparation
                   1228: To process 6to4 packets, the operating system kernel needs to know about them. 
                   1229: For that a driver has to be compiled in that knows about 6to4, and how to handle 
                   1230: it. In NetBSD 4.0 and newer, the driver is already present in GENERIC kernel 
                   1231: configurations, so the procedure below is usually unnecessary.
                   1233: For a NetBSD kernel, put the following into your kernel config file to prepare 
                   1234: it for using IPv6 and 6to4, e.g. on NetBSD use:
                   1236:     options INET6                 # IPv6
                   1237:     pseudo-device stf             # 6to4 IPv6 over IPv4 encapsulation
                   1239: Note that the 
                   1240: [stf(4)]( device is 
                   1241: not enabled by default on NetBSD releases older than 4.0. Rebuild your kernel, 
                   1242: then reboot your system to use the new kernel. Please consult
                   1243: [[Compiling the kernel|guide/kernel]] for further information on configuring, 
                   1244: building and installing a new kernel!
                   1246: ### 6to4 Setup
                   1248: This section describes the commands to setup 6to4. In short, the steps performed 
                   1249: here are:
                   1251:  1. Configure interface
                   1252:  2. Set default route
                   1253:  3. Setup Router Advertisement, if wanted
                   1255: The first step in setting up 6to4 is creating the 6to4 interface and assigning 
                   1256: an IPv6 address to it. This is achieved with the 
                   1257: [ifconfig(8)]( 
                   1258: command. Assuming the example configuration above, the commands for NetBSD are:
                   1260:     # ifconfig stf0 create
                   1261:     # ifconfig stf0 inet6 2002:3ee0:3972:1::1 prefixlen 16 alias
                   1263: After configuring the 6to4 device with these commands, routing needs to be 
                   1264: setup, to forward all tunneled IPv6 traffic to the 6to4 relay router. The best 
                   1265: way to do this is by setting a default route, the command to do so is, for 
                   1266: NetBSD:
                   1268:     # route add -inet6 default 2002:c058:6301::
                   1270: Note that NetBSD's 
                   1271: [stf(4)]( device 
                   1272: determines the IPv4 address of the 6to4 uplink from the routing table. Using 
                   1273: this feature, it is easy to setup your own 6to4 (uplink) gateway if you have an 
                   1274: IPv6 uplink, e.g. via 6Bone.
                   1276: After these commands, you are connected to the IPv6-enabled world - 
                   1277: Congratulations! Assuming name resolution is still done via IPv4, you can now 
                   1278: ping an IPv6-site like or
                   1280:     # /sbin/ping6
                   1282: As a final step in setting up IPv6 via 6to4, you will want to setup Router 
                   1283: Advertisement if you have several hosts on your network. While it is possible to 
                   1284: setup 6to4 on each node, doing so will result in very expensive routing from one 
                   1285: node to the other - packets will be sent to the remote 6to4 gateway, which will 
                   1286: then route the packets back to the neighbor node. Instead, setting up 6to4 on 
                   1287: one machine and talking native IPv6 on-wire is the preferred method of handling 
                   1288: things.
                   1290: The first step to do so is to assign an IPv6-address to your ethernet. In the 
                   1291: following example we will assume subnet `2` of the IPv6-net is used for the 
                   1292: local ethernet and the MAC address of the ethernet interface is 
                   1293: 12:34:56:78:9a:bc, i.e. your local gateway's ethernet interface's IP address 
                   1294: will be 2002:3ee0:3972:2:1234:56ff:fe78:9abc. Assign this address to your 
                   1295: ethernet interface, e.g.
                   1297:     # ifconfig ne0 inet6 alias 2002:3ee0:3972:2:1234:56ff:fe78:9abc
                   1299: Here, `ne0` is an example for your ethernet card interface. This will most 
                   1300: likely be different for your setup, depending on what kind of card is used.
                   1302: Next thing that needs to be ensured for setting up the router is that it will 
                   1303: actually forward packets from the local 6to4 device to the ethernet device and 
                   1304: back. To enable IPv6 packet forwarding, set `ip6mode=router` in NetBSD's 
                   1305: `/etc/rc.conf`, which will result in the `net.inet6.ip6.forwarding` sysctl being 
                   1306: set to `1`:
                   1308:     # sysctl -w net.inet6.ip6.forwarding=1
                   1310: ![Enabling packet forwarding is needed for a 6to4 router](/guide/images/ipv6-en-5forward.gif)  
                   1311: **Enabling packet forwarding is needed for a 6to4 router**
                   1313: To setup router advertisement on BSD, the file `/etc/rtadvd.conf` needs to be 
                   1314: checked. It allows configuration of many things, but usually the default config 
                   1315: of not containing any data is ok. With that default, IPv6 addresses found on all 
                   1316: of the router's network interfaces will be advertised.
                   1318: After checking the router advertisement configuration is correct and IPv6 
                   1319: forwarding is turned on, the daemon handling it can be started. Under NetBSD, it 
                   1320: is called `rtadvd`. Start it up either manually (for testing it the first time) 
                   1321: or via the system's startup scripts, and see all your local nodes automagically 
                   1322: configure the advertised subnet address in addition to their already-existing 
                   1323: link local address.
                   1325:     # rtadvd
                   1327: ### Quickstart using pkgsrc/net/hf6to4
                   1329: So far, we have described how 6to4 works and how to set it up manually. For an 
                   1330: automated way to make everything happen e.g. when going online, the 'hf6to4' 
                   1331: package is convenient. It will determine your IPv6 address from the IPv4 address 
                   1332: you got assigned by your provider, then set things up that you are connected.
                   1334: Steps to setup the pkgsrc/net/hf6to4 package are:
                   1336:  1. Install the package either by compiling it from pkgsrc, or by `pkg_add`'ing 
                   1337:     the 6to4-1.2 package.
                   1339:         # cd /usr/pkgsrc/net/hf6to4
                   1340:         # make install
                   1342:  2. Make sure you have the 
                   1343:     [stf(4)]( 
                   1344:     pseudo-device in your kernel, see above.
                   1346:  3. Configure the 'hf6to4' package. First, copy 
                   1347:     `/usr/pkg/share/examples/hf6to4/hf6to4.conf` to `/usr/pkg/etc/hf6to4.conf`, 
                   1348:     then adjust the variables. Note that the file is in /bin/sh syntax.
                   1350:         # cd /usr/pkg/etc
                   1351:         # cp ../share/examples/hf6to4/hf6to4.conf hf6to4.conf
                   1352:         # vi hf6to4.conf
                   1354:        Please see the 
                   1355:        [hf6to4(8)]( 
                   1356:        manpage for an explanation of all the variables you can set in 
                   1357:        `hf6to4.conf`. If you have dialup IP via PPP, and don't want to run Router 
                   1358:        Advertizing for other IPv6 machines on your home or office network, you 
                   1359:        don't need to configure anything. If you want to setup Router Advertising, 
                   1360:        you need to set the `in_if` to the internal (ethernet) interface, e.g.
                   1362:         $in_if="rtk0";            # Inside (ethernet) interface
                   1364:  4. Now dial up, then start the 6to4 command manually:
                   1366:         # /usr/pkg/sbin/hf6to4 start
                   1368:  5. After that, you should be connected, use 
                   1369:     [ping6(8)]( to 
                   1370:     see if everything works:
                   1372:         # ping6
                   1373:         PING6(56=40+8+8 bytes) 2002:d954:110b:1::1 --> 2001:4f8:4:7:2e0:81ff:fe52:9a6b
                   1374:         16 bytes from 2001:4f8:4:7:2e0:81ff:fe52:9a6b, icmp_seq=0 hlim=60 time=250.234 ms
                   1375:         16 bytes from 2001:4f8:4:7:2e0:81ff:fe52:9a6b, icmp_seq=1 hlim=60 time=255.652 ms
                   1376:         16 bytes from 2001:4f8:4:7:2e0:81ff:fe52:9a6b, icmp_seq=2 hlim=60 time=251.237 ms
                   1377:         ^C
                   1378:         --- ping6 statistics ---
                   1379:         3 packets transmitted, 3 packets received, 0.0% packet loss
                   1380:         round-trip min/avg/max/std-dev = 250.234/252.374/255.652/2.354 ms
                   1382:         # traceroute6
                   1383:         traceroute6 to (2001:4f8:4:7:2e0:81ff:fe52:9a6b)
                   1384:         from 2002:d954:110b:1::1, 64 hops max, 12 byte packets
                   1385:         1  2002:c25f:6cbf:1::1  66.31 ms  66.382 ms  69.062 ms
                   1386:         2  76.134 ms *  76.87 ms
                   1387:         3  76.371 ms  80.709 ms  79.482 ms
                   1388:         4  92.763 ms  90.863 ms  94.322 ms
                   1389:         5  116.115 ms  93.463 ms  96.331 ms
                   1390:         6  103.347 ms  99.334 ms  100.803 ms
                   1391:         7  99.481 ms  100.421 ms  100.119 ms
                   1392:         8  2001:798:28:300::2  89.711 ms  90.435 ms  90.035 ms
                   1393:         9  179.671 ms  185.141 ms  185.86 ms
                   1394:         10  177.067 ms  179.086 ms  178.05 ms
                   1395:         11  178.04 ms  179.727 ms  184.165 ms
                   1396:         12  249.856 ms  247.476 ms  249.012 ms
                   1397:         13  239.691 ms  241.404 ms  240.998 ms
                   1398:         14  247.541 ms  246.661 ms  246.359 ms
                   1399:         15  240.987 ms 239.056 ms  241.251 ms
                   1400:         16  240.868 ms  241.29 ms  242.337 ms
                   1401:         17  249.477 ms  250.4 ms  256.035 ms
                   1402:         18  2001:4f8:4:7:2e0:81ff:fe52:9a6b  268.164 ms  252.97 ms  252.366 ms 
                   1404:        Please note that `traceroute6` shows the v6 hops only, any underlying 
                   1405:        tunnels are invisible and thus not displayed.
                   1407:  6. If this works, you can put the following lines into your `/etc/ppp/ip-up` 
                   1408:     script to run the command each time you go online:
                   1410:         logger -p -t ip-up Configuring 6to4 IPv6
                   1411:         /usr/pkg/sbin/hf6to4 stop
                   1412:         /usr/pkg/sbin/hf6to4 start
                   1414:  7. If you want to route IPv6 for your LAN, you can instruct `` to setup 
                   1415:     Router Advertising for you too:
                   1417:         # /usr/pkg/sbin/hf6to4 rtadvd-start
                   1419:     You can put that command into `/etc/ppp/ip-up` as well to make it permanent.
                   1421:  8. If you have changed `/etc/ppp/ip-up` to setup 6to4 automatically, you will 
                   1422:        most likely want to change `/etc/ppp/ip-down` too, to shut it down when you 
                   1423:        go offline. Here's what to put into `/etc/ppp/ip-down`:
                   1425:         logger -p -t ip-down Shutting down 6to4 IPv6
                   1426:         /usr/pkg/sbin/hf6to4 rtadvd-stop
                   1427:         /usr/pkg/sbin/hf6to4 stop
                   1429: ### Known 6to4 Relay Routers
                   1431: It is normally not necessary to pick a specific 6to4 relay router, but if 
                   1432: necessary, you may find a list of known working routers at 
                   1433: [\~nsayer/6to4/]( In tests, 
                   1434: only and were found working. Cisco has one 
                   1435: that requires registration, see 
                   1436: [](
                   1438: There's also an experimental 6to4 server located in Germany, 
                   1439: This server runs under NetBSD 1.6 and was setup 
                   1440: using the configuration steps described above. The whole configuration of the 
                   1441: machine can be seen at 
                   1442: [](
                   1444: ### Tunneling 6to4 through an IPFilter firewall
                   1446: The 6to4 protocol encapsulates IPv6 packets in IPv4, and gives them their own IP 
                   1447: type, which most firewalls block as unknown, as their payload type is directly 
                   1448: `TCP`, `UDP` or `ICMP`. Usually, you want to setup your 6to4 gateway on the same 
                   1449: machine that is directly connected to the (IPv4) internet, and which usually 
                   1450: runs the firewall. For the case that you want to run your 6to4 gateway behind a 
                   1451: firewall, you need to drill a hole into the firewall, to let 6to4 packets 
                   1452: through. Here is how to do this!
                   1454: The example assumes that you use the `ppp0` interface on your firewall to 
                   1455: connect to the Internet.
                   1457: Put the following lines into `/etc/ipf.conf` to allow your IPFilter firewall let 
                   1458: all 6to4 packets pass (lines broken with `\` due to space restrictions; please 
                   1459: put them lines continued that way all in one line):
                   1461:     # Handle traffic by different rulesets
                   1462:     block in  quick on ppp0 all head 1
                   1463:     block out quick on ppp0 all head 2
                   1465:     ### Incoming packets:
                   1466:     # allow some IPv4:
                   1467:     pass  in  log quick on ppp0 proto tcp from any to any \
                   1468:     port = www flags S keep state keep frags  group 1
                   1469:     pass  in      quick on ppp0 proto tcp from any to any \
                   1470:     port = ssh keep state         group 1
                   1471:     pass  in      quick on ppp0 proto tcp from any to any \
                   1472:     port = mail keep state        group 1
                   1473:     pass  in  log quick on ppp0 proto tcp from any to any \
                   1474:     port = ftp keep state       group 1
                   1475:     pass  in  log quick on ppp0 proto tcp from any to any \
                   1476:     port = ftp-data keep state      group 1
                   1477:     pass  in  log quick on ppp0 proto icmp from any to any        group 1
                   1478:     # allow all IPv6:
                   1479:     pass in       quick on ppp0 proto ipv6       from any to any  group 1
                   1480:     pass in  log  quick on ppp0 proto ipv6-route from any to any  group 1
                   1481:     pass in  log  quick on ppp0 proto ipv6-frag  from any to any  group 1
                   1482:     pass in  log  quick on ppp0 proto ipv6-icmp  from any to any  group 1
                   1483:     pass in  log  quick on ppp0 proto ipv6-nonxt from any to any  group 1
                   1484:     pass in  log  quick on ppp0 proto ipv6-opts  from any to any  group 1
                   1485:     # block rest:
                   1486:     blockin  log  quick on ppp0 all                               group 1
                   1488:     ### Outgoing packets:
                   1489:     # allow usual stuff:
                   1490:     pass  out     quick on ppp0 proto  tcp from any to any flags S \
                   1491:     keep state keep frags group 2
                   1492:     pass  out     quick on ppp0 proto  udp from any to any         \
                   1493:     keep state keep frags group 2
                   1494:     pass  out     quick on ppp0 proto icmp from any to any         \
                   1495:     keep state            group 2
                   1496:     # allow all IPv6:
                   1497:     pass out      quick on ppp0 proto ipv6       from any to any  group 2
                   1498:     pass out log  quick on ppp0 proto ipv6-route from any to any  group 2
                   1499:     pass out log  quick on ppp0 proto ipv6-frag  from any to any  group 2
                   1500:     pass out log  quick on ppp0 proto ipv6-icmp  from any to any  group 2
                   1501:     pass out log  quick on ppp0 proto ipv6-nonxt from any to any  group 2
                   1502:     pass out log  quick on ppp0 proto ipv6-opts  from any to any  group 2
                   1503:     # block rest:
                   1504:     block out log quick on ppp0 all             group 2
                   1506: Now any host on your network can send (the `out` rules) and receive (the `in` 
                   1507: rules) v4-encapsulated IPv6 packets, allowing setup of any of them as a 6to4 
                   1508: gateway. Of course you only want to do this on one host and use native IPv6 
                   1509: between your hosts, and you may also want to enforce this with more restrictive 
                   1510: rulesets, please see 
                   1511: [ipf.conf(5)]( 
                   1512: for more information on IPFilter rules.
                   1514: After your firewall lets pass encapsulated IPv6 packets, you may want to set up 
                   1515: your 6to4 gateway to monitor the IPv6 traffic, or even restrict it. To do so, 
                   1516: you need to setup IPFilter on your 6to4 gateway as well. For basic monitoring, 
                   1517: enable `ipfilter=yes` in `/etc/rc.conf` and put the following into 
                   1518: `/etc/ipf6.conf`:
                   1520:     pass in  log quick on stf0 from any to any
                   1521:     pass out log quick on stf0 from any to any
                   1523: This logs all (IPv6) traffic going in and out of your `stf0` tunneling 
                   1524: interface. You can add filter rules as well if needed.
                   1526: If you are more interested in traffic stats than a general overview of your 
                   1527: network traffic, using MRTG in conjunction with the `net-snmp` package is 
                   1528: recommended instead of analyzing IPFilter log files.
                   1530: ### Conclusion & Further Reading
                   1532: Compared to where IPv4 is today, IPv6 is still in its early steps. It is 
                   1533: working, there are all sort of services and clients available, only the userbase 
                   1534: is missing. It is hoped the information provided here helps people better 
                   1535: understand what IPv6 is, and to start playing with it.
                   1537: A few links should be mentioned here for interested parties:
                   1539:  * An example script to setup 6to4 on BSD based machines is available at 
                   1540:    <>. The script determines your IPv6 
                   1541:    address and sets up 6to4 and (if wanted) router advertising. It was designed 
                   1542:    to work in dialup setups with changing IPv4 addresses.
                   1544:  * Given that there isn't a standard for IPv6 in Linux land today, there are 
                   1545:    different setup instructions for most distributions. The setup of IPv6 on 
                   1546:    Debian GNU/Linux can be found at 
                   1547:    [\~csmall/ipv6/setup.html](
                   1549:  * The BSD Unix implementations have their own IPv6 documentation each, 
                   1550:    interesting URLs are <> for NetBSD, 
                   1551:    <\_US.ISO8859-1/books/handbook/network-ipv6.html> 
                   1552:    for FreeBSD.
                   1554:  * Projects working on implementing IPv6 protocol stacks for free Unix like 
                   1555:    operating systems are KAME for BSD and USAGI for Linux. Their web sites can 
                   1556:    be found at <> and <>. A list 
                   1557:    of host and router implementations can be found at 
                   1558:    <>.
                   1560:  * Besides the official RFC archive at <>, information 
                   1561:    on IPv6 can be found at several web sites. First and foremost, the 6Bone's 
                   1562:    web page at <> must be mentioned. 6Bone was started as 
                   1563:    the testbed for IPv6, and is now an important part of the IPv6-connected 
                   1564:    world. Other web pages that contain IPv6-related contents include 
                   1565:    <>, <> and 
                   1566:    <>. Most of these sites carry further links - be 
                   1567:    sure to have a look!

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