1. Setting up TCP/IP on NetBSD in practice
    1. A walk through the kernel configuration
    2. Overview of the network configuration files
    3. Connecting to the Internet with a modem
      1. Getting the connection information
      2. resolv.conf and nsswitch.conf
      3. Creating the directories for pppd
      4. Connection script and chat file
      5. Note
      6. Authentication
      7. pppd options
      8. Testing the modem
      9. Activating the link
      10. Using a script for connection and disconnection
      11. Running commands after dialin
    4. Creating a small home network
    5. Setting up an Internet gateway with IPNAT
      1. Configuring the gateway/firewall
      2. Configuring the clients
      3. Some useful commands
    6. Setting up a network bridge device
      1. Bridge example
    7. A common LAN setup
    8. Connecting two PCs through a serial line
      1. Connecting NetBSD with BSD or Linux
      2. Linux
      3. Connecting NetBSD and Windows NT
      4. Connecting NetBSD and Windows 95
    9. IPv6 Connectivity & Transition via 6to4
      1. Getting 6to4 IPv6 up & running
      2. Obtaining IPv6 Address Space for 6to4
      3. How to get connected
      4. Security Considerations
      5. Data Needed for 6to4 Setup
      6. Kernel Preparation
      7. 6to4 Setup
      8. Quickstart using pkgsrc/net/hf6to4
      9. Known 6to4 Relay Routers
      10. Tunneling 6to4 through an IPFilter firewall
      11. Conclusion & Further Reading

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 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) manpage, and there is usually a manpage for each driver too, e.g. tlp(4).

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) 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 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 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) 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) 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) manpage and Next generation Internet protocol - IPv6 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) 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) 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) 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) 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) and ipf(8) manpages for more information on operation of IPFilter, and Configuring the gateway/firewall 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.


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) 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), ne(4), 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) 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) 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) 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) 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) 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).

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) 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) 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) 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) 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) 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) 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) 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.

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:

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 and


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/'
user alan

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) man page.


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

kdebug 4

You will get a log of the operations performed when the system tries to connect. See pppd(8), syslog.conf(5).

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/
'' ATDT0299999999

Note: If you have problems with the chat file, you can try connecting manually to the POP with the cu(1) program and verify the exact strings that you are receiving.


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:

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/
'' ATDT0299999999
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):


Check the pppd(8) 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) 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

    In the previous example the reset command (ATZ) was sent to the modem, which replied with OK: the communication works. To exit cu(1), 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). Cables are a frequent cause of trouble, too.

When you start cu(1) 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:

if [ -f /var/spool/lock/LCK..$MODEM ]; then
echo ppp is already running...
pppd call $POP
tail -f /var/log/messages

ppp-stop is used to close the connection:

if [ -f /var/spool/lock/LCK..$MODEM ]; then
echo -f killing pppd...
kill -HUP `cat /var/spool/lock/LCK..$MODEM`
echo done
echo ppp is not active

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) 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) 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 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
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 is assigned to the card.

# ifconfig ne0 inet netmask 0xffffff00

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

Repeating the previous command now gives a different result:

# ifconfig ne0
address: 00:50:ba:aa:a7:7f
media: Ethernet autoselect (10baseT)
inet netmask 0xffffff00 broadcast
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, 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 is the address of the active host:

# ping
PING ape ( 56 data bytes
64 bytes from icmp_seq=0 ttl=255 time=1.286 ms
64 bytes from icmp_seq=1 ttl=255 time=0.649 ms
64 bytes from icmp_seq=2 ttl=255 time=0.681 ms
64 bytes from icmp_seq=3 ttl=255 time=0.656 ms
----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:

ifconfig_ne0="inet 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:


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.
#             localhost
::1                   localhost
# RFC 1918 specifies that these networks are "internal".
# ape vespa

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 and it is setup to serve for "", put the following into /etc/resolv.conf:

# /etc/resolv.conf

The /etc/nsswitch.conf file should be checked as explained in the previous nsswitch.conf example.

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
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


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

# /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:

# /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 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:

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,, 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) 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:

        !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


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

On the second machine write the following commands:

# slattach /dev/tty00
# ifconfig sl0 inet

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

# ping

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.


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

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

The meaning of the first line will be explained later in this section; 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.

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:

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
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 ("RFC 1933: Transition Mechanisms for IPv6 Hosts and Routers"), and that's implemented e.g. by the gif(4) 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 ("RFC 3056: Connection of IPv6 Domains via IPv4 Clouds"), and that is implemented in the stf(4) 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 ("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. 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 216^ IPv6 subnets, which can take up to 264^ 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
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
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:

The NetBSD stf(4) 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:

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) 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 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) 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) 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 or

# /sbin/ping6

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
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) 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) 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): to see if everything works:

    # ping6
    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
    --- 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
    traceroute6 to (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  76.134 ms *  76.87 ms
    3  76.371 ms  80.709 ms  79.482 ms
    4  92.763 ms  90.863 ms  94.322 ms
    5  116.115 ms  93.463 ms  96.331 ms
    6  103.347 ms  99.334 ms  100.803 ms
    7  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  179.671 ms  185.141 ms  185.86 ms
    10  177.067 ms  179.086 ms  178.05 ms
    11  178.04 ms  179.727 ms  184.165 ms
    12  249.856 ms  247.476 ms  249.012 ms
    13  239.691 ms  241.404 ms  240.998 ms
    14  247.541 ms  246.661 ms  246.359 ms
    15  240.987 ms 239.056 ms  241.251 ms
    16  240.868 ms  241.29 ms  242.337 ms
    17  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 -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 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 -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\~nsayer/6to4/. In tests, only and were found working. Cisco has one that requires registration, see

There's also an experimental 6to4 server located in Germany, 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

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) 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: