File:  [NetBSD Developer Wiki] / wikisrc / guide / net-practice.mdwn
Revision 1.2: download - view: text, annotated - select for diffs
Thu Mar 14 23:19:08 2013 UTC (13 months ago) by jdf
Branches: MAIN
CVS tags: HEAD
Cosmetical issues.

# Setting up TCP/IP on NetBSD in practice

## A walk through the kernel configuration

Before we dive into configuring various aspects of network setup, we want to 
walk through the necessary bits that have to or can be present in the kernel. 
See [[Compiling the kernel|guide/kernel]] for more details on compiling the 
kernel, we will concentrate on the configuration of the kernel here. We will 
take the i386/GENERIC config file as an example here. Config files for other 
platforms should contain similar information, the comments in the config files 
give additional hints. Besides the information given here, each kernel option is 
also documented in the 
[options(4)](http://netbsd.gw.com/cgi-bin/man-cgi?options+4+NetBSD-5.0.1+i386) 
manpage, and there is usually a manpage for each driver too, e.g. 
[tlp(4)](http://netbsd.gw.com/cgi-bin/man-cgi?tlp+4+NetBSD-5.0.1+i386).

The first line of each config file shows the version. It can be used to compare 
against other versions via CVS, or when reporting bugs.

    options         NTP             # NTP phase/frequency locked loop

If you want to run the Network Time Protocol (NTP), this option can be enabled 
for maximum precision. If the option is not present, NTP will still work. See 
[ntpd(8)](http://netbsd.gw.com/cgi-bin/man-cgi?ntpd+8+NetBSD-5.0.1+i386) for 
more information.

    file-system     NFS             # Network File System client

If you want to use another machine's hard disk via the Network File System 
(NFS), this option is needed. The guide article about the
[[Network File System|guide/net-services#nfs]] gives more information on NFS.

    options         NFSSERVER       # Network File System server

This option includes the server side of the NFS remote file sharing protocol. 
Enable if you want to allow other machines to use your hard disk. The mentioned 
article in the guide about [[NFS|guide/net-services#nfs]] contains more 
information on NFS.

    #options        GATEWAY         # packet forwarding

If you want to setup a router that forwards packets between networks or network 
interfaces, setting this option is needed. It doesn't only switch on packet 
forwarding, but also increases some buffers. See 
[options(4)](http://netbsd.gw.com/cgi-bin/man-cgi?options+4+NetBSD-5.0.1+i386) 
for details.

    options         INET            # IP + ICMP + TCP + UDP

This enables the TCP/IP code in the kernel. Even if you don't want/use 
networking, you will still need this for machine-internal communication of 
subsystems like the X Window System. See 
[inet(4)](http://netbsd.gw.com/cgi-bin/man-cgi?inet+4+NetBSD-5.0.1+i386) for 
more details.

    options         INET6           # IPV6

If you want to use IPv6, this is your option. If you don't want IPv6, which is 
part of NetBSD since the 1.5 release, you can remove/comment out that option. 
See the 
[inet6(4)](http://netbsd.gw.com/cgi-bin/man-cgi?inet6+4+NetBSD-5.0.1+i386) 
manpage and [[Next generation Internet protocol - 
IPv6|guide/net-intro#ipv6-intro]] for more information on the next generation 
Internet protocol.

    #options        IPSEC           # IP security

Includes support for the IPsec protocol, including key and policy management, 
authentication and compression. This option can be used without the previous 
option INET6, if you just want to use IPsec with IPv4, which is possible. See 
[ipsec(4)](http://netbsd.gw.com/cgi-bin/man-cgi?ipsec+4+NetBSD-5.0.1+i386) for 
more information.

    #options        IPSEC_ESP       # IP security (encryption part; define w/IPSEC)

This option is needed in addition to IPSEC if encryption is wanted in IPsec.

    #options        MROUTING        # IP multicast routing

If multicast services like the MBone services should be routed, this option 
needs to be included. Note that the routing itself is controlled by the 
[mrouted(8)](http://netbsd.gw.com/cgi-bin/man-cgi?mrouted+8+NetBSD-5.0.1+i386) 
daemon.

    options         ISO,TPIP        # OSI
    #options        EON             # OSI tunneling over IP

These options include the OSI protocol stack, which was said for a long time to 
be the future of networking. It's mostly history these days. :-) See the 
[iso(4)](http://netbsd.gw.com/cgi-bin/man-cgi?iso+4+NetBSD-5.0.1+i386) manpage 
for more information.

    options         NETATALK        # AppleTalk networking protocols

Include support for the AppleTalk protocol stack. Userland server programs are 
needed to make use of that. See pkgsrc/net/netatalk and pkgsrc/net/netatalk-asun 
for such packages. More information on the AppleTalk protocol and protocol stack 
are available in the 
[atalk(4)](http://netbsd.gw.com/cgi-bin/man-cgi?atalk+4+NetBSD-5.0.1+i386) 
manpage.

    options         PPP_BSDCOMP     # BSD-Compress compression support for PPP
    options         PPP_DEFLATE     # Deflate compression support for PPP
    options         PPP_FILTER      # Active filter support for PPP (requires bpf)

These options tune various aspects of the Point-to-Point protocol. The first two 
determine the compression algorithms used and available, while the third one 
enables code to filter some packets.

    options         PFIL_HOOKS      # pfil(9) packet filter hooks
    options         IPFILTER_LOG    # ipmon(8) log support

These options enable firewalling in NetBSD, using IPFilter. See the 
[ipf(4)](http://netbsd.gw.com/cgi-bin/man-cgi?ipf+4+NetBSD-5.0.1+i386) and 
[ipf(8)](http://netbsd.gw.com/cgi-bin/man-cgi?ipf+8+NetBSD-5.0.1+i386) manpages 
for more information on operation of IPFilter, and [[Configuring the 
	gateway/firewall|guide/net-practice#ipnat-configuring-gateway]] for a 
	configuration example.

    # Compatibility with 4.2BSD implementation of TCP/IP.  Not recommended.
    #options        TCP_COMPAT_42

This option is only needed if you have machines on the network that still run 
4.2BSD or a network stack derived from it. If you've got one or more 
4.2BSD-systems on your network, you've to pay attention to set the right 
broadcast-address, as 4.2BSD has a bug in its networking code, concerning the 
broadcast address. This bug forces you to set all host-bits in the 
broadcast-address to `0`. The `TCP_COMPAT_42` option helps you ensuring this.

    options         NFS_BOOT_DHCP,NFS_BOOT_BOOTPARAM

These options enable lookup of data via DHCP or the BOOTPARAM protocol if the 
kernel is told to use a NFS root file system. See the 
[diskless(8)](http://netbsd.gw.com/cgi-bin/man-cgi?diskless+8+NetBSD-5.0.1+i386) 
manpage for more information.

    # Kernel root file system and dump configuration.
    config          netbsd  root on ? type ?
    #config         netbsd  root on sd0a type ffs
    #config         netbsd  root on ? type nfs

These lines tell where the kernel looks for its root file system, and which 
filesystem type it is expected to have. If you want to make a kernel that uses a 
NFS root filesystem via the tlp0 interface, you can do this with

    root on tlp0 type       nfs

If a `?` is used instead of a device/type, the kernel tries to 
figure one out on its own.

    # ISA serial interfaces
    com0    at isa? port 0x3f8 irq 4        # Standard PC serial ports
    com1    at isa? port 0x2f8 irq 3
    com2    at isa? port 0x3e8 irq 5

If you want to use PPP or SLIP, you will need some serial (com) interfaces. 
Others with attachment on USB, PCMCIA or PUC will do as well.

    # Network Interfaces

This rather long list contains all sorts of network drivers. Please pick the one 
that matches your hardware, according to the comments. For most drivers, there's 
also a manual page available, e.g. 
[tlp(4)](http://netbsd.gw.com/cgi-bin/man-cgi?tlp+4+NetBSD-5.0.1+i386), 
[ne(4)](http://netbsd.gw.com/cgi-bin/man-cgi?ne+4+NetBSD-5.0.1+i386), etc.

    # MII/PHY support

This section lists media independent interfaces for network cards. Pick one that 
matches your hardware. If in doubt, enable them all and see what the kernel 
picks. See the 
[mii(4)](http://netbsd.gw.com/cgi-bin/man-cgi?mii+4+NetBSD-5.0.1+i386) manpage 
for more information.

    # USB Ethernet adapters
    aue*    at uhub? port ?         # ADMtek AN986 Pegasus based adapters
    cue*    at uhub? port ?         # CATC USB-EL1201A based adapters
    kue*    at uhub? port ?         # Kawasaki LSI KL5KUSB101B based adapters

USB-ethernet adapters only have about 2MBit/s bandwidth, but they are very 
convenient to use. Of course this needs other USB related options which we won't 
cover here, as well as the necessary hardware. See the corresponding manpages 
for more information.

    # network pseudo-devices
    pseudo-device   bpfilter        8       # Berkeley packet filter

This pseudo-device allows sniffing packets of all sorts. It's needed for 
tcpdump, but also rarpd and some other applications that need to know about 
network traffic. See 
[bpf(4)](http://netbsd.gw.com/cgi-bin/man-cgi?bpf+4+NetBSD-5.0.1+i386) for more 
information.

    pseudo-device   ipfilter                # IP filter (firewall) and NAT

This one enables the IPFilter's packet filtering kernel interface used for 
firewalling, NAT (IP Masquerading) etc. See 
[ipf(4)](http://netbsd.gw.com/cgi-bin/man-cgi?ipf+4+NetBSD-5.0.1+i386) and 
[Configuring the gateway/firewall|guide/net-practice#ipnat-configuring-gateway]] 
for more information.

    pseudo-device   loop                    # network loopback

This is the `lo0` software loopback network device which is used by some 
programs these days, as well as for routing things. It should not be omitted. 
See [lo(4)](http://netbsd.gw.com/cgi-bin/man-cgi?lo+4+NetBSD-5.0.1+i386) for 
more details.

    pseudo-device   ppp             2       # Point-to-Point Protocol

If you want to use PPP either over a serial interface or ethernet (PPPoE), you 
will need this option. See 
[ppp(4)](http://netbsd.gw.com/cgi-bin/man-cgi?ppp+4+NetBSD-5.0.1+i386) for 
details on this interface.

    pseudo-device   sl              2       # Serial Line IP

Serial Line IP is a simple encapsulation for IP over (well :) serial lines. It 
does not include negotiation of IP addresses and other options, which is the 
reason that it's not in widespread use today any more. See 
[sl(4)](http://netbsd.gw.com/cgi-bin/man-cgi?sl+4+NetBSD-5.0.1+i386).

    pseudo-device   strip           2       # Starmode Radio IP (Metricom)

If you happen to have one of the old Metricom Ricochet packet radio wireless 
network devices, use this pseudo-device to use it. See the 
[strip(4)](http://netbsd.gw.com/cgi-bin/man-cgi?strip+4+NetBSD-5.0.1+i386) 
manpage for detailed information.

    pseudo-device   tun             2       # network tunneling over tty

This network device can be used to tunnel network packets to a device file, 
`/dev/tun*`. Packets routed to the tun0 interface can be read from `/dev/tun0`, 
and data written to `/dev/tun0` will be sent out the tun0 network interface. 
This can be used to implement e.g. QoS routing in userland. See 
[tun(4)](http://netbsd.gw.com/cgi-bin/man-cgi?tun+4+NetBSD-5.0.1+i386) for 
details.

    pseudo-device   gre             2       # generic L3 over IP tunnel

The GRE encapsulation can be used to tunnel arbitrary layer 3 packets over IP, 
e.g. to implement VPNs. See 
[gre(4)](http://netbsd.gw.com/cgi-bin/man-cgi?gre+4+NetBSD-5.0.1+i386) for more.

    pseudo-device   gif             4       # IPv[46] over IPv[46] tunnel (RFC 1933)

Using the GIF interface allows to tunnel e.g. IPv6 over IPv4, which can be used 
to get IPv6 connectivity if no IPv6-capable uplink (ISP) is available. Other 
mixes of operations are possible, too. See the 
[gif(4)](http://netbsd.gw.com/cgi-bin/man-cgi?gif+4+NetBSD-5.0.1+i386) manpage 
for some examples.

    #pseudo-device  faith           1       # IPv[46] tcp relay translation i/f

The faith interface captures IPv6 TCP traffic, for implementing userland 
IPv6-to-IPv4 TCP relays e.g. for protocol transitions. See the 
[faith(4)](http://netbsd.gw.com/cgi-bin/man-cgi?faith+4+NetBSD-5.0.1+i386) 
manpage for more details on this device.

    #pseudo-device  stf             1       # 6to4 IPv6 over IPv4 encapsulation

This adds a network device that can be used to tunnel IPv6 over IPv4 without 
setting up a configured tunnel before. The source address of outgoing packets 
contains the IPv4 address, which allows routing replies back via IPv4. See the 
[stf(4)](http://netbsd.gw.com/cgi-bin/man-cgi?stf+4+NetBSD-5.0.1+i386) manpage 
and [IPv6 Connectivity & Transition via 6to4|guide/net-practice#ipv6-6to4]] for 
more details.

    pseudo-device   vlan                    # IEEE 802.1q encapsulation

This interface provides support for IEEE 802.1Q Virtual LANs, which allows 
tagging Ethernet frames with a `vlan` ID. Using properly configured switches 
(that also have to support VLAN, of course), this can be used to build virtual 
LANs where one set of machines doesn't see traffic from the other (broadcast and 
other). The 
[vlan(4)](http://netbsd.gw.com/cgi-bin/man-cgi?vlan+4+NetBSD-5.0.1+i386) manpage 
tells more about this.

## Overview of the network configuration files

The following is a list of the files used to configure the network. The usage of 
these files, some of which have already been met the first chapters, will be 
described in the following sections.

 * `/etc/hosts` -- Local hosts database file. Each line contains information 
   regarding a known host and contains the internet address, the host's name and 
   the aliases. Small networks can be configured using only the hosts file, 
   without a *name server*.

 * `/etc/resolv.conf` -- This file specifies how the routines which provide 
   access to the Internet Domain Name System should operate. Generally it 
   contains the addresses of the name servers.

 * `/etc/ifconfig.xxx` -- This file is used for the automatic configuration of 
   the network card at boot.

 * `/etc/mygate` -- Contains the IP address of the gateway.

 * `/etc/nsswitch.conf` -- Name service switch configuration file. It controls 
   how a process looks up various databases containing information regarding 
   hosts, users, groups, etc. Specifically, this file defines the order to look 
   up the databases. For example, the line:

       hosts:    files dns

   specifies that the hosts database comes from two sources, *files* (the local 
   `/etc/hosts` file) and *DNS*, (the Internet Domain Name System) and that the 
   local files are searched before the DNS.

   It is usually not necessary to modify this file.

## Connecting to the Internet with a modem

There are many types of Internet connections: this section explains how to 
connect to a provider using a modem over a telephone line using the PPP 
protocol, a very common setup. In order to have a working connection, the 
following steps must be done:

 1. Get the necessary information from the provider.
 2. Edit the file `/etc/resolv.conf` and check `/etc/nsswitch.conf`.
 3. Create the directories `/etc/ppp` and `/etc/ppp/peers` if they don't exist.
 4. Create the connection script, the chat file and the pppd options file.
 5. Created the user-password authentication file.

Judging from the previous list it looks like a complicated procedure that 
requires a lot of work. Actually, the single steps are very easy: it's just a 
matter of modifying, creating or simply checking some small text files. In the 
following example it will be assumed that the modem is connected to the second 
serial port `/dev/tty01` (COM2 in DOS).

A few words on the difference between `com`, `COM` and `tty`. For NetBSD, `com` 
is the name of the serial port driver (the one that is displayed by `dmesg`) and 
`tty` is the name of the port. Since numbering starts at 0, `com0` is the driver 
for the first serial port, named `tty00`. In the DOS world, instead, `COM1` 
refers to the first serial port (usually located at 0x3f8), `COM2` to the 
second, and so on. Therefore `COM1` (DOS) corresponds to `/dev/tty00` (NetBSD).

Besides external modems connected to COM ports (using `/dev/tty0[012]` on i386, 
`/dev/tty[ab]` on sparc, ...) modems on USB (`/dev/ttyU*`) and pcmcia/cardbus 
(`/dev/tty0[012]`) can be used.

### Getting the connection information

The first thing to do is ask the provider the necessary information for the 
connection, which means:

 * The phone number of the nearest POP.
 * The authentication method to be used.
 * The username and password for the connection.
 * The IP addresses of the name servers.

### resolv.conf and nsswitch.conf

The `/etc/resolv.conf` file must be configured using the information supplied by 
the provider, especially the addresses of the DNS. In this example the two DNS 
will be `194.109.123.2` and `191.200.4.52`:

    nameserver 194.109.123.2
    nameserver 191.200.4.52

And now an example of the `/etc/nsswitch.conf` file:

    # /etc/nsswitch.conf
    group:         compat
    group_compat:  nis
    hosts:         files dns
    netgroup:      files [notfound=return] nis
    networks:      files
    passwd:        compat
    passwd_compat: nis
    shells:        files

The defaults of doing hostname lookups via `/etc/hosts` followed by the DNS 
works fine and there's usually no need to modify this.

### Creating the directories for pppd

The directories `/etc/ppp` and `/etc/ppp/peers` will contain the configuration 
files for the PPP connection. After a fresh install of NetBSD they don't exist 
and must be created (chmod 700).

    # mkdir /etc/ppp
    # mkdir /etc/ppp/peers 

### Connection script and chat file

The connection script will be used as a parameter on the pppd command line; it 
is located in `/etc/ppp/peers` and has usually the name of the provider. For 
example, if the provider's name is BigNet and your user name for the connection 
to the provider is alan, an example connection script could be:

    # /etc/ppp/peers/bignet
    connect '/usr/sbin/chat -v -f /etc/ppp/peers/bignet.chat'
    noauth
    user alan
    remotename bignet.it

In the previous example, the script specifies a *chat file* to be used for the 
connection. The options in the script are detailed in the 
[pppd(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pppd+8+NetBSD-5.0.1+i386) man 
page.

### Note

If you are experiencing connection problems, add the following two lines to the 
connection script

    debug
    kdebug 4

You will get a log of the operations performed when the system tries to connect. 
See [pppd(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pppd+8+NetBSD-5.0.1+i386), 
[syslog.conf(5)](http://netbsd.gw.com/cgi-bin/man-cgi?syslog.conf+5+NetBSD-5.0.1+i386).

The connection script calls the chat application to deal with the physical 
connection (modem initialization, dialing, ...) The parameters to chat can be 
specified inline in the connection script, but it is better to put them in a 
separate file. If, for example, the telephone number of the POP to call is
`02 99999999`, an example chat script could be:

    # /etc/ppp/peers/bignet.chat
    ABORT BUSY
    ABORT "NO CARRIER"
    ABORT "NO DIALTONE"
    '' ATDT0299999999
    CONNECT ''

*Note*: If you have problems with the chat file, you can try connecting manually 
to the POP with the 
[cu(1)](http://netbsd.gw.com/cgi-bin/man-cgi?cu+1+NetBSD-5.0.1+i386) program and 
verify the exact strings that you are receiving.

### Authentication

During authentication each of the two systems verifies the identity of the other 
system, although in practice you are not supposed to authenticate the provider, 
but only to be verified by him, using one of the following methods:

 * PAP/CHAP
 * login

Most providers use a PAP/CHAP authentication.

#### PAP/CHAP authentication

The authentication information (speak: password) is stored in the 
`/etc/ppp/pap-secrets` for PAP and in `/etc/ppp/chap-secrets` for CHAP. The 
lines have the following format:

    user * password

For example:

    alan * pZY9o

For security reasons the `pap-secrets` and `chap-secrets` files should be owned 
by root and have permissions 600.

    # chown root /etc/ppp/pap-secrets
    # chown root /etc/ppp/chap-secrets
    # chmod 600 /etc/ppp/pap-secrets
    # chmod 600 /etc/ppp/chap-secrets

#### Login authentication

This type of authentication is not widely used today; if the provider uses login 
authentication, user name and password must be supplied in the chat file instead 
of the PAP/CHAP files, because the chat file simulates an interactive login. In 
this case, set up appropriate permissions for the chat file.

The following is an example chat file with login authentication:

    # /etc/ppp/peers/bignet.chat
    ABORT BUSY
    ABORT "NO CARRIER"
    ABORT "NO DIALTONE"
    '' ATDT0299999999
    CONNECT ''
    TIMEOUT 50
    ogin: alan
    ssword: pZY9o

### pppd options

The only thing left to do is the creation of the pppd options file, which is 
`/etc/ppp/options` (chmod 644):

    /dev/tty01
    lock
    crtscts
    57600
    modem
    defaultroute
    noipdefault

Check the 
[pppd(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pppd+8+NetBSD-5.0.1+i386) man 
page for the meaning of the options.

### Testing the modem

Before activating the link it is a good idea to make a quick modem test, in 
order to verify that the physical connection and the communication with the 
modem works. For the test the 
[cu(1)](http://netbsd.gw.com/cgi-bin/man-cgi?cu+1+NetBSD-5.0.1+i386) program can 
be used, as in the following example.

 1. Create the file `/etc/uucp/port` with the following lines:

        type modem
        port modem
        device /dev/tty01
        speed 115200

    (substitute the correct device in place of `/dev/tty01`).

 2. Write the command `cu -p modem` to start sending commands to the modem. For 
    example:

        # cu -p modem
        Connected.
        ATZ
        OK
        ~.
        
        Disconnected.
        #

	In the previous example the reset command (ATZ) was sent to the modem, which 
	replied with OK: the communication works. To exit 
	[cu(1)](http://netbsd.gw.com/cgi-bin/man-cgi?cu+1+NetBSD-5.0.1+i386), write 
	`~` (tilde) followed by `.` (dot), as in the example.

If the modem doesn't work, check that it is connected to the correct port (i.e. 
you are using the right port with 
[cu(1)](http://netbsd.gw.com/cgi-bin/man-cgi?cu+1+NetBSD-5.0.1+i386). Cables are 
a frequent cause of trouble, too.

When you start 
[cu(1)](http://netbsd.gw.com/cgi-bin/man-cgi?cu+1+NetBSD-5.0.1+i386) and a 
message saying `Permission denied` appears, check who is the owner of the 
`/dev/tty##` device, it must be "uucp". For example:

    $ ls -l /dev/tty00
    crw-------  1 uucp  wheel  8, 0 Mar 22 20:39 /dev/tty00

If the owner is root, the following happens:

    $ ls -l /dev/tty00
    crw-------  1 root  wheel  8, 0 Mar 22 20:39 /dev/tty00
    $ cu -p modem
    cu: open (/dev/tty00): Permission denied
    cu: All matching ports in use

### Activating the link

At last everything is ready to connect to the provider with the following 
command:

    # pppd call bignet

where `bignet` is the name of the already described connection script. To see 
the connection messages of pppd, give the following command:

    # tail -f /var/log/messages

To disconnect, do a `kill -HUP` of `pppd`.

     # pkill -HUP pppd 

### Using a script for connection and disconnection

When the connection works correctly, it's time to write a couple of scripts to 
avoid repeating the commands every time. These two scripts can be named, for 
example, `ppp-start` and `ppp-stop`.

`ppp-start` is used to connect to the provider:

    #!/bin/sh
    MODEM=tty01
    POP=bignet
    if [ -f /var/spool/lock/LCK..$MODEM ]; then
    echo ppp is already running...
    else
    pppd call $POP
    tail -f /var/log/messages
    fi

`ppp-stop` is used to close the connection:

    #!/bin/sh
    MODEM=tty01
    if [ -f /var/spool/lock/LCK..$MODEM ]; then
    echo -f killing pppd...
    kill -HUP `cat /var/spool/lock/LCK..$MODEM`
    echo done
    else
    echo ppp is not active
    fi

The two scripts take advantage of the fact that when pppd is active, it creates 
the file `LCK..tty01` in the `/var/spool/lock` directory. This file contains the 
process ID (*pid*) of the pppd process.

The two scripts must be executable:

    # chmod u+x ppp-start ppp-stop

### Running commands after dialin

If you find yourself to always run the same set of commands each time you dial 
in, you can put them in a script `/etc/ppp/ip-up` which will be called by 
[pppd(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pppd+8+NetBSD-5.0.1+i386) after 
successful dial-in. Likewise, before the connection is closed down, 
`/etc/ppp/ip-down` is executed. Both scripts are expected to be executable. See 
[pppd(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pppd+8+NetBSD-5.0.1+i386) for 
more details.

## Creating a small home network

Networking is one of the main strengths of Unix and NetBSD is no exception: 
networking is both powerful and easy to set up and inexpensive too, because 
there is no need to buy additional software to communicate or to build a server. 
[[Setting up an Internet gateway with IPNAT|guide/net-practice#ipnat]] explains 
how to configure a NetBSD machine to act as a gateway for a network: with IPNAT 
all the hosts of the network can reach the Internet with a single connection to 
a provider made by the gateway machine. The only thing to be checked before 
creating the network is to buy network cards supported by NetBSD (check the 
`INSTALL.*` files for a list of supported devices).

First, the network cards must be installed and connected to a hub, switch or 
directly (see the next image for an example configuration).

Next, check that the network cards are recognized by the kernel, studying the 
output of the `dmesg` command. In the following example the kernel recognized 
correctly an NE2000 clone:

    ...
    ne0 at isa0 port 0x280-0x29f irq 9
    ne0: NE2000 Ethernet
    ne0: Ethernet address 00:c2:dd:c1:d1:21
    ...

If the card is not recognized by the kernel, check that it is enabled in the 
kernel configuration file and then that the card's IRQ matches the one that the 
kernel expects. For example, this is the isa NE2000 line in the configuration 
file; the kernel expects the card to be at IRQ 9.

    ...
    ne0 at isa? port 0x280 irq 9 # NE[12]000 ethernet cards
    ...

If the card's configuration is different, it will probably not be found at boot. 
In this case, either change the line in the kernel configuration file and 
compile a new kernel or change the card's setup (usually through a setup disk 
or, for old cards, a jumper on the card).

The following command shows the network card's current configuration:

    # ifconfig ne0
    ne0: flags=8822<BROADCAST,NOTRAILERS,SIMPLEX,MULTICAST> mtu 1500
    address: 00:50:ba:aa:a7:7f
    media: Ethernet autoselect (10baseT)
    inet6 fe80::250:baff:feaa:a77f%ne0 prefixlen 64 scopeid 0x1 

The software configuration of the network card is very easy. The IP address 
192.168.1.1 is assigned to the card.

    # ifconfig ne0 inet 192.168.1.1 netmask 0xffffff00

Note that the networks 10.0.0.0/8 and 192.168.0.0/16 are reserved for private 
networks, which is what we're setting up here.

Repeating the previous command now gives a different result:

    # ifconfig ne0
    ne0: flags=8863<UP,BROADCAST,NOTRAILERS,RUNNING,SIMPLEX,MULTICAST> mtu 1500
    address: 00:50:ba:aa:a7:7f
    media: Ethernet autoselect (10baseT)
    inet 192.168.1.1 netmask 0xffffff00 broadcast 192.168.1.255
    inet6 fe80::250:baff:feaa:a77f%ne0 prefixlen 64 scopeid 0x1 

The output of `ifconfig` has now changed: the IP address is now printed and 
there are two new flags, `UP` and `RUNNING` If the interface isn't `UP`, it will 
not be used by the system to send packets.

The host was given the IP address 192.168.1.1, which belongs to the set of 
addresses reserved for internal networks which are not reachable from the 
Internet. The configuration is finished and must now be tested; if there is 
another active host on the network, a `ping` can be tried. For example, if 
192.168.1.2 is the address of the active host:

    # ping 192.168.1.2
    PING ape (192.168.1.2): 56 data bytes
    64 bytes from 192.168.1.2: icmp_seq=0 ttl=255 time=1.286 ms
    64 bytes from 192.168.1.2: icmp_seq=1 ttl=255 time=0.649 ms
    64 bytes from 192.168.1.2: icmp_seq=2 ttl=255 time=0.681 ms
    64 bytes from 192.168.1.2: icmp_seq=3 ttl=255 time=0.656 ms
    ^C
    ----ape PING Statistics----
    4 packets transmitted, 4 packets received, 0.0% packet loss
    round-trip min/avg/max/stddev = 0.649/0.818/1.286/0.312 ms

With the current setup, at the next boot it will be necessary to repeat the 
configuration of the network card. In order to avoid repeating the card's 
configuration at each boot, add the following lines to `/etc/rc.conf`:

    auto_ifconfig=yes
    ifconfig_ne0="inet 192.168.1.1 netmask 0xffffff00" 

In this example the variable `ifconfig_ne0` was set because the network card was 
recognized as *ne0* by the kernel; if you are using a different adapter, 
substitute the appropriate name in place of ne0.

At the next boot the network card will be configured automatically.

If you have a router that is connected to the internet, you can use it as 
default router, which will handle all your packets. To do so, set `defaultroute` 
to the router's IP address in `/etc/rc.conf`:

    defaultroute=192.168.0.254

Be sure to use the default router's IP address instead of name, in case your DNS 
server is beyond the default router. In that case, the DNS server couldn't be 
reached to resolve the default router's hostname and vice versa, creating a 
chicken-and-egg problem.

To reach hosts on your local network, and assuming you really have very few 
hosts, adjust `/etc/hosts` to contain the addresses of all the hosts belonging 
to the internal network. For example:

    #
    # Host Database
    # This file should contain the addresses and aliases
    # for local hosts that share this file.
    # It is used only for "ifconfig" and other operations
    # before the nameserver is started.
    #
    #
    127.0.0.1             localhost
    ::1                   localhost
    #
    # RFC 1918 specifies that these networks are "internal".
    # 10.0.0.0    10.255.255.255
    # 172.16.0.0  172.31.255.255
    # 192.168.0.0 192.168.255.255
    
    192.168.1.1   ape.insetti.net ape
    192.168.1.2   vespa.insetti.net vespa
    192.168.1.0   insetti.net

If you are dialed in via an Internet Service Provider, or if you have a local 
Domain Name Server (DNS) running, you may want to use it to resolve hostnames to 
IP addresses, possibly in addition to `/etc/hosts`, which would only know your 
own hosts. To configure a machine as DNS client, you need to edit 
`/etc/resolv.conf`, and enter the DNS server's address, in addition to an 
optional domain name that will be appended to hosts with no domain, in order to 
create a FQDN for resolving. Assuming your DNS server's IP address is 
192.168.1.2 and it is setup to serve for "home.net", put the following into 
`/etc/resolv.conf`:

    # /etc/resolv.conf
    domain home.net
    nameserver 192.168.1.2

The `/etc/nsswitch.conf` file should be checked as explained in the previous 
[[nsswitch.conf example|guide/net-practice#rc.conf_and_nsswitch.conf]].

Summing up, to configure the network the following must be done: the network 
adapters must be installed and physically connected. Next they must be 
configured (with `ifconfig`) and, finally, the file `/etc/rc.conf` must be 
modified to configure the interface and possibly default router, and 
`/etc/resolv.conf` and `/etc/nsswitch.conf` should be adjusted if DNS should be 
used. This type of network management is sufficient for small networks without 
sophisticated needs.

## Setting up an Internet gateway with IPNAT

The mysterious acronym IPNAT hides the Internet Protocol Network Address 
Translation, which enables the routing of an internal network (e.g. your home 
network as described in the previous section) on a real network (Internet). This 
means that with only one *real* IP, static or dynamic, belonging to a gateway 
running IPNAT, it is possible to create simultaneous connections to the Internet 
for all the hosts of the internal network.

Some usage examples of IPNAT can be found in the subdirectory 
`/usr/share/examples/ipf`: look at the files `BASIC.NAT` and `nat-setup`.

The setup for the example described in this section is detailed in the following 
figure: *host 1* can connect to the Internet calling a provider with a modem and 
getting a dynamic IP address. *host 2* and *host 3* can't communicate with the 
Internet with a normal setup: IPNAT allows them to do it: host 1 will act as a 
Internet gateway for hosts 2 and 3. Using host 1 as default router, hosts 2 and 
3 will be able to access the Internet.

![Network with gateway](/guide/images/net1.gif)  
**Network with gateway**

### Configuring the gateway/firewall

To use IPNAT, the *pseudo-device ipfilter* must be compiled into the kernel, and 
IP packet forwarding must be enabled in the kernel. To check, run:

    # sysctl net.inet.ip.forwarding
    net.inet.ip.forwarding = 1

If the result is `1` as in the previous example, the option is enabled, 
otherwise, if the result is `0` the option is disabled. You can do two things:

 1. Compile a new kernel, with the GATEWAY option enabled.

 2. Enable the option in the current kernel with the following command:

        # sysctl -w net.inet.ip.forwarding=1

	You can add sysctl settings to `/etc/sysctl.conf` to have them set 
	automatically at boot. In this case you would want to add

        net.inet.ip.forwarding=1


The rest of this section explains how to create an IPNAT configuration that is 
automatically started every time that a connection to the provider is activated 
with the PPP link. With this configuration all the host of a home network (for 
example) will be able to connect to the Internet through the gateway machine, 
even if they don't use NetBSD.

For the setup, first, create the `/etc/ipnat.conf` file containing the following 
rules:

    map ppp0 192.168.1.0/24 -> 0/32 proxy port ftp ftp/tcp
    map ppp0 192.168.1.0/24 -> 0/32 portmap tcp/udp 40000:60000
    map ppp0 192.168.1.0/24 -> 0/32

192.168.1.0/24 are the network addresses that should be mapped. The first line 
of the configuration file is optional: it enables active FTP to work through the 
gateway. The second line is used to handle correctly tcp and udp packets; the 
portmapping is necessary because of the many to one relationship). The third 
line is used to enable ICMP, ping, etc.

Next, create the `/etc/ppp/ip-up` file; it will be called automatically every 
time that the PPP link is activated:

    #!/bin/sh
    # /etc/ppp/ip-up
    /etc/rc.d/ipnat forcestart

Create the file `/etc/ppp/ip-down`; it will be called automatically when the PPP 
link is closed:

    #!/bin/sh
    # /etc/ppp/ip-down
    /etc/rc.d/ipnat forcestop

Both `ip-up` and `ip-down` must be executable:

    # chmod u+x ip-up ip-down

The gateway machine is now ready.

### Configuring the clients

Create a `/etc/resolv.conf` file like the one on the gateway machine, to make 
the clients access the same DNS server as the gateway.

Next, make all clients use the gateway as their default router. Use the 
following command:

    # route add default 192.168.1.1

192.168.1.1 is the address of the gateway machine configured in the previous 
section.

Of course you don't want to give this command every time, so it's better to 
define the `defaultroute` entry in the `/etc/rc.conf` file: the default route 
will be set automatically during system initialization, using the defaultroute 
option as an argument to the `route add default` command.

If the client machine is not using NetBSD, the configuration will be different. 
On Windows PCs you need to set the gateway property of the TCP/IP protocol to 
the IP address of the NetBSD gateway.

That's all that needs to be done on the client machines.

### Some useful commands

The following commands can be useful for diagnosing problems:

 * `ping` -- tries to connect to other computers via ICMP (usually used for 
   testing if a connection exists).
 * `netstat -r` -- Displays the routing tables (similar to `route show`).
 * `traceroute` -- On the client it shows the route followed by the packets to 
   their destination.
 * `tcpdump` -- Use on the gateway to monitor TCP/IP traffic.

## Setting up a network bridge device

A bridge can be used to combine different physical networks into one logical 
network, i.e. connect them at layer 2 of the ISO-OSI model, not at layer 3, 
which is what a router would do. The NetBSD `bridge` driver provides bridge 
functionality on NetBSD systems.

### Bridge example

In this example two physical networks are going to be combined in one logical 
network, 192.168.1.0, using a NetBSD bridge. The NetBSD machine which is going 
to act as bridge has two interfaces, ne0 and ne1, which are each connected to 
one physical network.

The first step is to make sure support for the `bridge` is compiled in the 
running kernel. Support is included in the GENERIC kernel.

When the system is ready the bridge can be created, this can be done using the 
[brconfig(8)]((http://netbsd.gw.com/cgi-bin/man-cgi?brconfig+8+NetBSD-current))
command. First of a bridge interface has to be created. With the following 
`ifconfig` command the `bridge0` interface will be created:

    $ ifconfig bridge0 create

Please make sure that at this point both the ne0 and ne1 interfaces are up. The 
next step is to add the ne0 and ne1 interfaces to the bridge.

    $ brconfig bridge0 add ne0 add ne1 up

This configuration can be automatically set up by creating an 
`/etc/ifconfig.interface` file, in this case `/etc/ifconfig.bridge0`, with the 
following contents:

    create
            !brconfig $int add ne0 add ne1 up

After setting up the bridge the bridge configuration can be displayed using the 
`brconfig -a` command. Remember that if you want to give the bridge machine an 
IP address you can only allocate an IP address to one of the interfaces which 
are part of the bridge.

## A common LAN setup

The small home network discussed in the previous section contained many items 
that were configured manually. In bigger LANs that are centrally managed, one 
can expect Internet connectivity being available via some router, a DNS server 
being available, and most important, a DHCP server which hands out IP addresses 
to clients on request. To make a NetBSD client run in such an environment, it's 
usually enough to set

    dhclient=yes

in `/etc/rc.conf`, and the IP address will be set automatically, 
`/etc/resolv.conf` will be created and routing setup to the default router.

## Connecting two PCs through a serial line

If you need to transfer files between two PCs which are not networked there is a 
simple solution which is particularly handy when copying the files to a floppy 
is not practical: the two machines can be networked with a serial cable (a *null 
modem* cable). The following sections describe some configurations.

### Connecting NetBSD with BSD or Linux

The easiest case is when both machines run NetBSD: making a connection with the 
SLIP protocol is very easy. On the first machine write the following commands:

    # slattach /dev/tty00
    # ifconfig sl0 inet 192.168.1.1 192.168.1.2

On the second machine write the following commands:

    # slattach /dev/tty00
    # ifconfig sl0 inet 192.168.1.2 192.168.1.1

Now you can test the connection with `ping`; for example, on the second PC 
write:

    # ping 192.168.1.1

If everything worked there is now an active network connection between the two 
machines and ftp, telnet and other similar commands can be executed. The textual 
aliases of the machines can be written in the `/etc/hosts` file.

 * In the previous example both PCs used the first serial port (`/dev/tty0`). 
   Substitute the appropriate device if you are using another port.

 * IP addresses like 192.168.x.x are reserved for `internal` networks. The first 
   PC has address 192.168.1.1 and the second 192.168.1.2.

 * To achieve a faster connection the `-s speed` option to `slattach` can be 
   specified.

 * `ftp` can be used to transfer files only if inetd is active and the ftpd 
 * server is enabled.

### Linux

If one of the two PCs runs Linux, the commands are slightly different (on the 
Linux machine only). If the Linux machine gets the 192.168.1.2 address, the 
following commands are needed:

    # slattach -p slip -s 115200 /dev/ttyS0 &
    # ifconfig sl0 192.168.1.2 pointopoint 192.168.1.1 up
    # route add 192.168.1.1 dev sl0

Don't forget the `&` in the first command.

### Connecting NetBSD and Windows NT

NetBSD and Windows NT can be (almost) easily networked with a serial *null 
modem* cable. Basically what needs to be done is to create a *Remote Access* 
connection under Windows NT and to start pppd on NetBSD.

Start pppd as root after having created a `.ppprc` in `/root`. Use the following 
example as a template.

    connect '/usr/sbin/chat -v CLIENT CLIENTSERVER'
    local
    tty00
    115200
    crtscts
    lock
    noauth
    nodefaultroute
    :192.168.1.2

The meaning of the first line will be explained later in this section; 
192.168.1.2 is the IP address that will be assigned by NetBSD to the Windows NT 
host; `tty00` is the serial port used for the connection (first serial port).

On the NT side a *null modem* device must be installed from the Control Panel 
(Modem icon) and a Remote Access connection using this modem must be created. 
The null modem driver is standard under Windows NT 4 but it's not a 100% null 
modem: when the link is activated, NT sends the string CLIENT and expects to 
receive the answer CLIENTSERVER. This is the meaning of the first line of the 
`.ppprc` file: `chat` must answer to NT when the connection is activated or 
the connection will fail.

In the configuration of the Remote Access connection the following must be 
specified: use the null modem, telephone number `1` (it's not used, anyway), PPP 
server, enable only TCP/IP protocol, use IP address and nameservers from the 
server (NetBSD in this case). Select the hardware control flow and set the port 
to 115200 8N1.

Now everything is ready to activate the connection.

 * Connect the serial ports of the two machines with the null modem cable.
 * Launch pppd on NetBSD. To see the messages of pppd:
   `tail -f /var/log/messages`).
 * Activate the Remote Access connection on Windows NT.

### Connecting NetBSD and Windows 95

The setup for Windows 95 is similar to the one for Windows NT: Remote Access on 
Windows 95 and the PPP server on NetBSD will be used. Most (if not all) Windows 
95 releases don't have the *null modem* driver, which makes things a little more 
complicated. The easiest solution is to find one of the available null modem 
drivers on the Internet (it's a small `.INF` file) and repeat the same steps as 
for Windows NT. The only difference is that the first line of the `.ppprc` file 
(the one that calls `chat`) can be removed.

If you can't find a real null modem driver for Windows 95 it's still possible to 
use a little trick:

 * Create a Remote Access connection like the one described before for Windows 
   NT, but using the *Standard Modem*.

 * In `.ppprc` substitute the line that calls `chat` with the following line

       connect '/usr/sbin/chat -v ATH OK AT OK ATE0V1 OK AT OK ATDT CONNECT'

 * Activate the connection as described in the section before for Windows NT.


In this way the `chat` program, called when the connection is activated, 
emulates what Windows 95 thinks is a standard modem, returning to Windows 95 the 
same answers that a standard modem would return. Whenever Windows 95 sends a 
modem command string, `chat` returns OK.

## IPv6 Connectivity & Transition via 6to4

This section will concentrate on how to get network connectivity for IPv6 and - 
as that is rarely available directly - talk at length about the alternatives to 
native IPv6 connectivity as a transitional method until native IPv6 peers are 
available.

Finding an ISP that offers IPv6 natively needs quite some luck. What you need 
next is a router that will be able to handle the traffic. To date, not all 
router manufacturers offer IPv6 or hardware accelerated IPv6 features, and 
gateway NAT boxes only rarely support IPv6 and also block IPv6 tunnels. An 
alternative approach involves configuring a standard PC running NetBSD to act as 
a router. The base NetBSD system contains a complete IPv6 routing solution, and 
for special routing needs software like Zebra can provide additional routing 
protocols. This solution is rather common for sites that want IPv6 
connectivity today. The drawbacks are that you need an ISP that supports 
IPv6 and that you may need a dedicated uplink only for IPv6.

IPv6 to-the-door may be rare, but you can still get IPv6 connectivity by using 
tunnels. Instead of talking IPv6 on the wire, the IPv6 packets are encapsulated 
in IPv4 packets, as shown in the next image. Using the existing IPv4 
infrastructure, the encapsulated packets are sent to a IPv6-capable uplink that 
will then remove the encapsulation, and forward the IPv6 packets.

![A frequently used method for transition is tunneling IPv6 in IPv4 packets](/guide/images/ipv6-en-2tunnel.gif)  
**A frequently used method for transition is tunneling IPv6 in IPv4 packets**

When using tunnels, there are two possibilities. One is to use a so-called 
*configured* tunnel, the other is called an *automatic* tunnel. A *configured* 
tunnel is one that required preparation from both ends of the tunnel, usually 
connected with some kind of registration to exchange setup information. An 
example for such a configured tunnel is the IPv6-over-IPv4 encapsulation 
described in
[RFC1933](http://tools.ietf.org/html/rfc1933) ("RFC 1933: Transition Mechanisms 
for IPv6 Hosts and Routers"), and that's implemented e.g. by the 
[gif(4)](http://netbsd.gw.com/cgi-bin/man-cgi?gif+4+NetBSD-5.0.1+i386) 
device found in NetBSD.

An *automatic* tunnel consists of a public server that has some kind of IPv6 
connectivity, e.g. via 6Bone. That server has made its connectivity data public, 
and also runs a tunneling protocol that does not require an explicit 
registration of the sites using it as uplink. A well-used example of such a 
protocol is the 6to4 mechanism described in
[RFC3056](http://tools.ietf.org/html/rfc3056) ("RFC 3056: Connection of IPv6 
Domains via IPv4 Clouds"), and that is implemented in the 
[stf(4)](http://netbsd.gw.com/cgi-bin/man-cgi?stf+4+NetBSD-5.0.1+i386) device 
found in NetBSD's. Another mechanism that does not require registration of 
IPv6-information is the 6over4 mechanism, which implements transporting of IPv6 
over a multicast-enabled IPv4 network, instead of e.g. ethernet or FDDI.  6over4 
is documented in [RFC2529](http://tools.ietf.org/html/rfc2529) ("RFC 2529: 
Transmission of IPv6 over IPv4 Domains without Explicit Tunnels"). It's main 
drawback is that you do need existing multicast infrastructure. If you don't 
have that, setting it up is about as much effort as setting up a configured IPv6 
tunnel directly, so it's usually not worth bothering in that case.

### Getting 6to4 IPv6 up & running

6to4 is an easy way to get IPv6 connectivity for hosts that only have an IPv4 
uplink, especially if you have the background given in
[[the chapter about IPv6|guide/net-intro#ipv6-intro]]. It can be used with 
static as well as dynamically assigned IPv4 addresses, e.g. as found in modem 
dialup scenarios today. When using dynamic IPv4 addresses, a change of IP 
addresses will be a problem for incoming traffic, i.e. you can't run persistent 
servers.

Example configurations given in this section are for NetBSD 1.5.2.

### Obtaining IPv6 Address Space for 6to4

The 6to4 IPv6 setup on your side doesn't consist of a single IPv6 address; 
Instead, you get a whole /48 network! The IPv6 addresses are derived from your 
(single) IPv4 address. The address prefix *2002:` is reserved for 6to4 based 
addresses (i.e. IPv6 addresses derived from IPv4 addresses). The next 32 bits 
are your IPv4 address. This results in a /48 network that you can use for your 
very own purpose. It leaves 16 bits space for 2^16^ IPv6 subnets, which can take 
up to 2^64^ nodes each. The next figure illustrates the building of your IPv6 
address (range) from your IPv4 address.

Thanks to the 6to4 prefix and your worldwide unique IPv4 address, this address 
block is unique, and it's mapped to your machine carrying the IPv4 address in 
question.

![6to4 derives an IPv6 from an IPv4 address](/guide/images/ipv6-en-3adr.gif)  
**6to4 derives an IPv6 from an IPv4 address**

### How to get connected

In contrast to the configured *IPv6-over-IPv4 tunnel* setup, you do not have to 
register at a 6bone-gateway, which would only then forward your IPv6 traffic 
encapsulated in IPv4. Instead, as your IPv6 address is derived from your IPv4 
address, inbound traffic can be sent through the nearest 6to4 relay router. 
De-encapsulation of the packet is done via a 6to4-capable network interface, 
which then forwards the resulting IPv6 packet according to your routing setup 
(in case you have more than one machine connected on your 6to4 assigned 
network).

To transmit IPv6 packets, the 6to4 router will encapsulate them inside IPv4 
packets; a system performing these functions is called a 6to4 border router. 
These packets have a default route to the *6to4 relay anycast prefix*. This 
anycast prefix will route the tunnel to a *6to4 relay router*.

![Request and reply can be routed via different gateways in 6to4](/guide/images/ipv6-en-1scene.gif)  
**Request and reply can be routed via different gateways in 6to4**

### Security Considerations

In contrast to the *configured tunnel* setup, you usually can't setup packet 
filters to block 6to4-packets from unauthorized sources, as this is exactly how 
(and why) 6to4 works at all. As such, malicious users can send packets with 
invalid/hazardous IPv6 payload. If you don't already filter on your border 
gateways anyways, packets with the following characteristics should not be 
allowed as valid 6to4 packets, and some firewalling seems to be justified for 
them:

 * unspecified IPv4 source/destination address: 0.0.0.0/8
 * loopback address in outer (v4) source/destination: 127.0.0.0/8
 * IPv4 multicast in source/destination: 224.0.0.0/4
 * limited broadcasts: 255.0.0.0/8
 * subnet broadcast address as source/destination: depends on your IPv4 setup

The NetBSD 
[stf(4)](http://netbsd.gw.com/cgi-bin/man-cgi?stf+4+NetBSD-5.0.1+i386) manual 
page documents some common configuration mistakes intercepted by default by the 
KAME stack as well as some further advice on filtering, but keep in mind that 
because of the requirement of these filters, 6to4 is not perfectly secure. 
Still, if forged 6to4 packets become a problem, you can use IPsec authentication 
to ensure the IPv6 packets are not modified.

### Data Needed for 6to4 Setup

In order to setup and configure IPv6 over 6to4, a few bits of configuration data 
must be known in advance. These are:

 * Your local IPv4 address. It can be determined using either the `ifconfig -a` 
   or `netstat -i` commands on most Unix systems. If you use a NATing gateway or 
   something, be sure to use the official, outside-visible address, not your 
   private (10/8 or 192.168/16) one.

   We will use 62.224.57.114 as the local IPv4 address in our example.

 * Your local IPv6 address, as derived from the IPv4 address. See the previous 
   figure ("6to4 derives an IPv6 from an IPv4 address") about how to do so.

   For our example, this is 2002:3ee0:3972:0001::1 (62.224.57.114 == 0x3ee03972, 
   0001::1 arbitrarily chosen).

 * The *6to4 IPv6 relay anycast address*. which is 2002:c058:6301::, or the IPv6 
   address of a specific 6to4 relay router you want to use. The IPv6 address 
   will do, as it also contains the IPv4 address in the usual 6to4 translation.

### Kernel Preparation

To process 6to4 packets, the operating system kernel needs to know about them. 
For that a driver has to be compiled in that knows about 6to4, and how to handle 
it. In NetBSD 4.0 and newer, the driver is already present in GENERIC kernel 
configurations, so the procedure below is usually unnecessary.

For a NetBSD kernel, put the following into your kernel config file to prepare 
it for using IPv6 and 6to4, e.g. on NetBSD use:

    options INET6                 # IPv6
    pseudo-device stf             # 6to4 IPv6 over IPv4 encapsulation

Note that the 
[stf(4)](http://netbsd.gw.com/cgi-bin/man-cgi?stf+4+NetBSD-5.0.1+i386) device is 
not enabled by default on NetBSD releases older than 4.0. Rebuild your kernel, 
then reboot your system to use the new kernel. Please consult
[[Compiling the kernel|guide/kernel]] for further information on configuring, 
building and installing a new kernel!

### 6to4 Setup

This section describes the commands to setup 6to4. In short, the steps performed 
here are:

 1. Configure interface
 2. Set default route
 3. Setup Router Advertisement, if wanted

The first step in setting up 6to4 is creating the 6to4 interface and assigning 
an IPv6 address to it. This is achieved with the 
[ifconfig(8)](http://netbsd.gw.com/cgi-bin/man-cgi?ifconfig+8+NetBSD-5.0.1+i386) 
command. Assuming the example configuration above, the commands for NetBSD are:

    # ifconfig stf0 create
    # ifconfig stf0 inet6 2002:3ee0:3972:1::1 prefixlen 16 alias

After configuring the 6to4 device with these commands, routing needs to be 
setup, to forward all tunneled IPv6 traffic to the 6to4 relay router. The best 
way to do this is by setting a default route, the command to do so is, for 
NetBSD:

    # route add -inet6 default 2002:c058:6301::

Note that NetBSD's 
[stf(4)](http://netbsd.gw.com/cgi-bin/man-cgi?stf+4+NetBSD-5.0.1+i386) device 
determines the IPv4 address of the 6to4 uplink from the routing table. Using 
this feature, it is easy to setup your own 6to4 (uplink) gateway if you have an 
IPv6 uplink, e.g. via 6Bone.

After these commands, you are connected to the IPv6-enabled world - 
Congratulations! Assuming name resolution is still done via IPv4, you can now 
ping an IPv6-site like www.kame.net or www6.NetBSD.org:

    # /sbin/ping6 www.kame.net

As a final step in setting up IPv6 via 6to4, you will want to setup Router 
Advertisement if you have several hosts on your network. While it is possible to 
setup 6to4 on each node, doing so will result in very expensive routing from one 
node to the other - packets will be sent to the remote 6to4 gateway, which will 
then route the packets back to the neighbor node. Instead, setting up 6to4 on 
one machine and talking native IPv6 on-wire is the preferred method of handling 
things.

The first step to do so is to assign an IPv6-address to your ethernet. In the 
following example we will assume subnet `2` of the IPv6-net is used for the 
local ethernet and the MAC address of the ethernet interface is 
12:34:56:78:9a:bc, i.e. your local gateway's ethernet interface's IP address 
will be 2002:3ee0:3972:2:1234:56ff:fe78:9abc. Assign this address to your 
ethernet interface, e.g.

    # ifconfig ne0 inet6 alias 2002:3ee0:3972:2:1234:56ff:fe78:9abc

Here, `ne0` is an example for your ethernet card interface. This will most 
likely be different for your setup, depending on what kind of card is used.

Next thing that needs to be ensured for setting up the router is that it will 
actually forward packets from the local 6to4 device to the ethernet device and 
back. To enable IPv6 packet forwarding, set `ip6mode=router` in NetBSD's 
`/etc/rc.conf`, which will result in the `net.inet6.ip6.forwarding` sysctl being 
set to `1`:

    # sysctl -w net.inet6.ip6.forwarding=1

![Enabling packet forwarding is needed for a 6to4 router](/guide/images/ipv6-en-5forward.gif)  
**Enabling packet forwarding is needed for a 6to4 router**

To setup router advertisement on BSD, the file `/etc/rtadvd.conf` needs to be 
checked. It allows configuration of many things, but usually the default config 
of not containing any data is ok. With that default, IPv6 addresses found on all 
of the router's network interfaces will be advertised.

After checking the router advertisement configuration is correct and IPv6 
forwarding is turned on, the daemon handling it can be started. Under NetBSD, it 
is called `rtadvd`. Start it up either manually (for testing it the first time) 
or via the system's startup scripts, and see all your local nodes automagically 
configure the advertised subnet address in addition to their already-existing 
link local address.

    # rtadvd

### Quickstart using pkgsrc/net/hf6to4

So far, we have described how 6to4 works and how to set it up manually. For an 
automated way to make everything happen e.g. when going online, the 'hf6to4' 
package is convenient. It will determine your IPv6 address from the IPv4 address 
you got assigned by your provider, then set things up that you are connected.

Steps to setup the pkgsrc/net/hf6to4 package are:

 1. Install the package either by compiling it from pkgsrc, or by `pkg_add`'ing 
    the 6to4-1.2 package.

        # cd /usr/pkgsrc/net/hf6to4
        # make install

 2. Make sure you have the 
    [stf(4)](http://netbsd.gw.com/cgi-bin/man-cgi?stf+4+NetBSD-5.0.1+i386) 
    pseudo-device in your kernel, see above.

 3. Configure the 'hf6to4' package. First, copy 
    `/usr/pkg/share/examples/hf6to4/hf6to4.conf` to `/usr/pkg/etc/hf6to4.conf`, 
    then adjust the variables. Note that the file is in /bin/sh syntax.

        # cd /usr/pkg/etc
        # cp ../share/examples/hf6to4/hf6to4.conf hf6to4.conf
        # vi hf6to4.conf

	Please see the 
	[hf6to4(8)](http://netbsd.gw.com/cgi-bin/man-cgi?hf6to4+8+NetBSD-5.0.1+i386) 
	manpage for an explanation of all the variables you can set in 
	`hf6to4.conf`. If you have dialup IP via PPP, and don't want to run Router 
	Advertizing for other IPv6 machines on your home or office network, you 
	don't need to configure anything. If you want to setup Router Advertising, 
	you need to set the `in_if` to the internal (ethernet) interface, e.g.

        $in_if="rtk0";            # Inside (ethernet) interface

 4. Now dial up, then start the 6to4 command manually:

        # /usr/pkg/sbin/hf6to4 start

 5. After that, you should be connected, use 
    [ping6(8)](http://netbsd.gw.com/cgi-bin/man-cgi?ping6+8+NetBSD-5.0.1+i386): to 
    see if everything works:

        # ping6 www.NetBSD.org
        PING6(56=40+8+8 bytes) 2002:d954:110b:1::1 --> 2001:4f8:4:7:2e0:81ff:fe52:9a6b
        16 bytes from 2001:4f8:4:7:2e0:81ff:fe52:9a6b, icmp_seq=0 hlim=60 time=250.234 ms
        16 bytes from 2001:4f8:4:7:2e0:81ff:fe52:9a6b, icmp_seq=1 hlim=60 time=255.652 ms
        16 bytes from 2001:4f8:4:7:2e0:81ff:fe52:9a6b, icmp_seq=2 hlim=60 time=251.237 ms
        ^C
        --- www.NetBSD.org ping6 statistics ---
        3 packets transmitted, 3 packets received, 0.0% packet loss
        round-trip min/avg/max/std-dev = 250.234/252.374/255.652/2.354 ms
        
        # traceroute6 www.NetBSD.org
        traceroute6 to www.NetBSD.org (2001:4f8:4:7:2e0:81ff:fe52:9a6b)
        from 2002:d954:110b:1::1, 64 hops max, 12 byte packets
        1  2002:c25f:6cbf:1::1  66.31 ms  66.382 ms  69.062 ms
        2  nr-erl1.6win.dfn.de  76.134 ms *  76.87 ms
        3  nr-fra1.6win.dfn.de  76.371 ms  80.709 ms  79.482 ms
        4  dfn.de6.de.6net.org  92.763 ms  90.863 ms  94.322 ms
        5  de.nl6.nl.6net.org  116.115 ms  93.463 ms  96.331 ms
        6  nl.uk6.uk.6net.org  103.347 ms  99.334 ms  100.803 ms
        7  uk1.uk61.uk.6net.org  99.481 ms  100.421 ms  100.119 ms
        8  2001:798:28:300::2  89.711 ms  90.435 ms  90.035 ms
        9  ge-1-0-0-2.r20.londen03.uk.bb.verio.net  179.671 ms  185.141 ms  185.86 ms
        10  p16-0-0-0.r81.nycmny01.us.bb.verio.net  177.067 ms  179.086 ms  178.05 ms
        11  p16-1-1-3.r20.nycmny01.us.bb.verio.net  178.04 ms  179.727 ms  184.165 ms
        12  p16-0-1-1.r20.mlpsca01.us.bb.verio.net  249.856 ms  247.476 ms  249.012 ms
        13  p64-0-0-0.r21.snjsca04.us.bb.verio.net  239.691 ms  241.404 ms  240.998 ms
        14  p64-0-0-0.r21.plalca01.us.bb.verio.net  247.541 ms  246.661 ms  246.359 ms
        15  xe-0-2-0.r20.plalca01.us.bb.verio.net  240.987 ms 239.056 ms  241.251 ms
        16  ge-6-1.a01.snfcca05.us.ra.verio.net  240.868 ms  241.29 ms  242.337 ms
        17  fa-5-2.a01.snfcca05.us.ce.verio.net  249.477 ms  250.4 ms  256.035 ms
        18  2001:4f8:4:7:2e0:81ff:fe52:9a6b  268.164 ms  252.97 ms  252.366 ms 

	Please note that `traceroute6` shows the v6 hops only, any underlying 
	tunnels are invisible and thus not displayed.

 6. If this works, you can put the following lines into your `/etc/ppp/ip-up` 
    script to run the command each time you go online:

        logger -p user.info -t ip-up Configuring 6to4 IPv6
        /usr/pkg/sbin/hf6to4 stop
        /usr/pkg/sbin/hf6to4 start

 7. If you want to route IPv6 for your LAN, you can instruct `6to4.pl` to setup 
    Router Advertising for you too:

        # /usr/pkg/sbin/hf6to4 rtadvd-start

    You can put that command into `/etc/ppp/ip-up` as well to make it permanent.

 8. If you have changed `/etc/ppp/ip-up` to setup 6to4 automatically, you will 
	most likely want to change `/etc/ppp/ip-down` too, to shut it down when you 
	go offline. Here's what to put into `/etc/ppp/ip-down`:

        logger -p user.info -t ip-down Shutting down 6to4 IPv6
        /usr/pkg/sbin/hf6to4 rtadvd-stop
        /usr/pkg/sbin/hf6to4 stop

### Known 6to4 Relay Routers

It is normally not necessary to pick a specific 6to4 relay router, but if 
necessary, you may find a list of known working routers at 
[http://www.kfu.com/\~nsayer/6to4/](http://www.kfu.com/~nsayer/6to4/). In tests, 
only 6to4.kfu.com and 6to4.ipv6.microsoft.com were found working. Cisco has one 
that requires registration, see 
[http://www.cisco.com/ipv6/](http://www.cisco.com/ipv6/).

There's also an experimental 6to4 server located in Germany, 
6to4.ipv6.fh-regensburg.de. This server runs under NetBSD 1.6 and was setup 
using the configuration steps described above. The whole configuration of the 
machine can be seen at 
[http://www.feyrer.de/IPv6/netstart.local](http://www.feyrer.de/IPv6/netstart.local).

### Tunneling 6to4 through an IPFilter firewall

The 6to4 protocol encapsulates IPv6 packets in IPv4, and gives them their own IP 
type, which most firewalls block as unknown, as their payload type is directly 
`TCP`, `UDP` or `ICMP`. Usually, you want to setup your 6to4 gateway on the same 
machine that is directly connected to the (IPv4) internet, and which usually 
runs the firewall. For the case that you want to run your 6to4 gateway behind a 
firewall, you need to drill a hole into the firewall, to let 6to4 packets 
through. Here is how to do this!

The example assumes that you use the `ppp0` interface on your firewall to 
connect to the Internet.

Put the following lines into `/etc/ipf.conf` to allow your IPFilter firewall let 
all 6to4 packets pass (lines broken with `\` due to space restrictions; please 
put them lines continued that way all in one line):

    # Handle traffic by different rulesets
    block in  quick on ppp0 all head 1
    block out quick on ppp0 all head 2
    
    ### Incoming packets:
    # allow some IPv4:
    pass  in  log quick on ppp0 proto tcp from any to any \
    port = www flags S keep state keep frags  group 1
    pass  in      quick on ppp0 proto tcp from any to any \
    port = ssh keep state         group 1
    pass  in      quick on ppp0 proto tcp from any to any \
    port = mail keep state        group 1
    pass  in  log quick on ppp0 proto tcp from any to any \
    port = ftp keep state       group 1
    pass  in  log quick on ppp0 proto tcp from any to any \
    port = ftp-data keep state      group 1
    pass  in  log quick on ppp0 proto icmp from any to any        group 1
    # allow all IPv6:
    pass in       quick on ppp0 proto ipv6       from any to any  group 1
    pass in  log  quick on ppp0 proto ipv6-route from any to any  group 1
    pass in  log  quick on ppp0 proto ipv6-frag  from any to any  group 1
    pass in  log  quick on ppp0 proto ipv6-icmp  from any to any  group 1
    pass in  log  quick on ppp0 proto ipv6-nonxt from any to any  group 1
    pass in  log  quick on ppp0 proto ipv6-opts  from any to any  group 1
    # block rest:
    blockin  log  quick on ppp0 all                               group 1
    
    ### Outgoing packets:
    # allow usual stuff:
    pass  out     quick on ppp0 proto  tcp from any to any flags S \
    keep state keep frags group 2
    pass  out     quick on ppp0 proto  udp from any to any         \
    keep state keep frags group 2
    pass  out     quick on ppp0 proto icmp from any to any         \
    keep state            group 2
    # allow all IPv6:
    pass out      quick on ppp0 proto ipv6       from any to any  group 2
    pass out log  quick on ppp0 proto ipv6-route from any to any  group 2
    pass out log  quick on ppp0 proto ipv6-frag  from any to any  group 2
    pass out log  quick on ppp0 proto ipv6-icmp  from any to any  group 2
    pass out log  quick on ppp0 proto ipv6-nonxt from any to any  group 2
    pass out log  quick on ppp0 proto ipv6-opts  from any to any  group 2
    # block rest:
    block out log quick on ppp0 all             group 2

Now any host on your network can send (the `out` rules) and receive (the `in` 
rules) v4-encapsulated IPv6 packets, allowing setup of any of them as a 6to4 
gateway. Of course you only want to do this on one host and use native IPv6 
between your hosts, and you may also want to enforce this with more restrictive 
rulesets, please see 
[ipf.conf(5)](http://netbsd.gw.com/cgi-bin/man-cgi?ipf.conf+5+NetBSD-5.0.1+i386) 
for more information on IPFilter rules.

After your firewall lets pass encapsulated IPv6 packets, you may want to set up 
your 6to4 gateway to monitor the IPv6 traffic, or even restrict it. To do so, 
you need to setup IPFilter on your 6to4 gateway as well. For basic monitoring, 
enable `ipfilter=yes` in `/etc/rc.conf` and put the following into 
`/etc/ipf6.conf`:

    pass in  log quick on stf0 from any to any
    pass out log quick on stf0 from any to any

This logs all (IPv6) traffic going in and out of your `stf0` tunneling 
interface. You can add filter rules as well if needed.

If you are more interested in traffic stats than a general overview of your 
network traffic, using MRTG in conjunction with the `net-snmp` package is 
recommended instead of analyzing IPFilter log files.

### Conclusion & Further Reading

Compared to where IPv4 is today, IPv6 is still in its early steps. It is 
working, there are all sort of services and clients available, only the userbase 
is missing. It is hoped the information provided here helps people better 
understand what IPv6 is, and to start playing with it.

A few links should be mentioned here for interested parties:

 * An example script to setup 6to4 on BSD based machines is available at 
   <http://www.NetBSD.org/packages/net/hf6to4/>. The script determines your IPv6 
   address and sets up 6to4 and (if wanted) router advertising. It was designed 
   to work in dialup setups with changing IPv4 addresses.

 * Given that there isn't a standard for IPv6 in Linux land today, there are 
   different setup instructions for most distributions. The setup of IPv6 on 
   Debian GNU/Linux can be found at 
   [http://people.debian.org/\~csmall/ipv6/setup.html](http://people.debian.org/~csmall/ipv6/setup.html).

 * The BSD Unix implementations have their own IPv6 documentation each, 
   interesting URLs are <http://www.NetBSD.org/docs/network/ipv6/> for NetBSD, 
   <http://www.freebsd.org/doc/en\_US.ISO8859-1/books/handbook/network-ipv6.html> 
   for FreeBSD.

 * Projects working on implementing IPv6 protocol stacks for free Unix like 
   operating systems are KAME for BSD and USAGI for Linux. Their web sites can 
   be found at <http://www.kame.net/> and <http://www.linux-ipv6.org/>. A list 
   of host and router implementations can be found at 
   <http://playground.sun.com/pub/ipng/html/ipng-implementations.html>.

 * Besides the official RFC archive at <ftp://ftp.isi.edu/in-notes>, information 
   on IPv6 can be found at several web sites. First and foremost, the 6Bone's 
   web page at <http://www.6bone.net/> must be mentioned. 6Bone was started as 
   the testbed for IPv6, and is now an important part of the IPv6-connected 
   world. Other web pages that contain IPv6-related contents include 
   <http://www.ipv6.org/>, <http://playground.sun.com/pub/ipng/html/> and 
   <http://www.ipv6forum.com/>. Most of these sites carry further links - be 
   sure to have a look!


CVSweb for NetBSD wikisrc <wikimaster@NetBSD.org> software: FreeBSD-CVSweb