IPv6 router guide

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This guide provides details on setting up IPv6 routing on a Gentoo Linux system.

Installation

Kernel

Any kernels version v2.6.0 or higher can support IPv6.

root #emerge --ask sys-kernel/gentoo-sources
KERNEL Required IPv6 options
[*] Networking support --->
    Networking options --->
        <M> The IPv6 protocol --->

Emerge

root #emerge --ask sys-apps/iproute2
root #emerge --ask net-misc/radvd
Tip
The ipv6 USE variable may need to be enabled for some packages, and can be added to /etc/portage/make.conf.

Additional software

There are a few packages which specifically deal with IPv6 items. Most of these are located in the net-misc category.

Package Description
net-misc/radvd Router advertisement daemon
net-misc/dhcpd ISC DHCP server, DHCPv4 and DHCPv6 capability
net-misc/dibbler DHCPv6 server
net-misc/ipv6calc Converts an IPv6 address to a compressed format
dev-perl/Socket6 IPv6 related part of the C socket.h defines and structure manipulators

Confirming IPv6 status

If IPv6 is enabled, the loopback device should show an IPv6 address:

root #ip -6 addr show lo
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever

Configuration

Obtaining an address and prefix

dhcpcd can be used to obtain a single, host only, /128 IPv6 address for the WAN interface, and a /64 IPv6 prefix for the LAN interface.

FILE /etc/dhcpcd.confRequest a IPv6 prefix for eth0.lan and eth0.management to be routed publicly with eth0.wan.
# Disable router solicitations for all interfaces, enable only for selected ones
noipv6rs
 
# Interface configuration for the wan vlan on the eth0 interface
interface eth0.wan
  # Enable router solicitation for this interface
  ipv6rs
  # Request a normal address usins iaid 1 for interface eth0.wan
  ia_na 1
  # Request a prefix using iaid 2 and assign it to the eth0.lan interface using sla_id 0 and prefix size of 64
  ia_pd 2 eth0.lan/0/64
See also
Dhcpcd
Warning
rfc6177 is barely seen as a recommendation by residential ISPs, Prefix Delegation may not work.

Enable forwarding

IPv6 packet forwarding must be enabled in kernel before a system can function as a router, this can be done using sysctl:

root #sysctl -w net.ipv6.conf.all.forwarding=1
Important
The radvd init script used later enables (and disables) forwarding, making the next step unnecessary.

To assign IPv6 addresses to clients, the IPv6 specification allows both methods, stateless and stateful IP assignment. The IPv6 Stateless Address Autoconfiguration uses a process called Router Advertisement and allows clients to obtain an IP and a default route by simply bringing an interface up. It is called "stateless" because there is no record of IPs assigned and the host they are assigned to. Stateful assignment is handled by DHCPv6. It is "stateful" because the server keeps a state of the clients who have requested IPs and received them.

Note
The IPv6 Stateless Address Autoconfiguration configures IP routing and connectivity, the DHCPv6 is required to assign IPv6 addresses, and provide information such as DNS servers.

Stateless configuration

Stateless configuration is easily accomplished using the Router Advertisement Daemon, or radvd:

/etc/radvd.conf is used to configure radvd, and is not created by default. If the IPv6 prefix configuration is left empty, the already assigned or configured IPv6 prefix is used:

FILE /etc/radvd.confRouter Advertisement (RA) configuration for the eth0.lan interface.
interface eth0.lan
{
        # Enable sending advertisements on this interface
        AdvSendAdvert on;
        # Set the Managed flag, allowing DHCPv6 (optional)
        AdvManagedFlag on;
        # Define prefix specific settings, based on the assigned prefix
        prefix ::/64
        {
                # Advertise when this link comes up
                AdvOnLink on;
                # Advertise RFC 4862 compliance
                AdvAutonomous on;
        };
};
Important
The Router Advertisements (RA) are send periodically on the eth0.lan interface to the all-nodes multicast address. Using an interface connected to the LAN, local area network.
Tip
Further information is available in man radvd.conf.

Stateful configuration

Warning
Dibbler project is concluded.

To have a stateful configuration, install and configure net-misc/dibbler.

root #emerge --ask dibbler

Configure the dibbler client by editing /etc/dibbler/client.conf.

CODE Sample dibbler client configuration
iface ppp0 {
	rapid-commit yes
	pd
	option dns-server
}

Now start the dibbler client, and configure it to start at boot:

root #/etc/init.d/dibbler-client start
root #rc-update add dibbler-client default

Service

OpenRC

To start radvd and start it on boot:

root #/etc/init.d/radvd start
root #rc-update add radvd default

DNS setup

IPv6 and DNS

Just as DNS for IPv4 uses A records, DNS for IPv6 uses AAAA records. (This is because IPv4 is an address space of 2^32 while IPv6 is an address space of 2^128). For reverse DNS, the INT standard is deprecated but still widely supported. ARPA is the latest standard. Support for the ARPA format will be described here.

BIND configuration

Recent versions of BIND include excellent IPv6 support. This section will assume at least minimal knowledge about the configuration and use of BIND. We will assume that bind is not running in a chroot. If this assumption is wrong, simply append the chroot prefix to most of the paths in the following section.

First add entries for both forward and reverse DNS zone files in /etc/bind/named.conf.

FILE /etc/bind/named.confnamed.conf entries
## (We allow bind to listen to IPv6 addresses.
## Using 'any' is the only way to do it prior to bind-9.3)
options {
    [...]
    listen-on-v6 { any; }
    [...]
};
## (This will provide the forward DNS for the domain 'ipv6-rules.com':)
zone "ipv6-rules.com" IN {
    type master;
    file "pri/ipv6-rules.com";
};
## (This format for reverse DNS is "bitwise." It's done by taking the IPv6 prefix,
## reversing the order of the numbers and putting a period between each number)
zone "6.9.2.0.0.0.f.1.0.7.4.0.1.0.0.2.ip6.arpa" {
        type master;
        file "pri/rev-ipv6-rules.com.arpa";
};

Now zone files and entries will need added for all hosts:

FILE /etc/bind/pri/ipv6-rules.com
$TTL    2h
@       IN      SOA     ipv6-rules.com. webmaster.ipv6-rules.com.  (
                                2003052501 ; Serial
                                28800      ; Refresh
                                14400      ; Retry
                                3600000    ; Expire
                                86400 )    ; Minimum
                NS      ns1.ipv6-rules.com
 
IN      AAAA    2001:470:1f00:296::1 ; address for ipv6-rules.com
host1   IN      AAAA    2001:470:1f00:296::2 ; address for host1.ipv6-rules.com
host2   IN      AAAA    2001:470:1f00:296::3:3 ; address for host2.ipv6-rules.com
FILE /etc/bind/pri/ipv6-rules.com.arpa
$TTL 3d ; Default TTL (bind 8 needs this, bind 9 ignores it)
@       IN SOA ipv6-rules.com. webmaster.ipv6-rules.com. (
                        2003052501      ; Serial number (YYYYMMdd)
                        24h             ; Refresh time
                        30m             ; Retry time
                        2d              ; Expire time
                        3d )            ; Default TTL
        IN      NS     ns1.ipv6-rules.com.
; IPv6 PTR entries
$ORIGIN 6.9.2.0.0.0.f.1.0.7.4.0.1.0.0.2.ip6.arpa.
 
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0 IN      PTR     ipv6-rules.com.
2.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0 IN      PTR     host1.ipv6-rules.com.
3.0.0.0.3.0.0.0.0.0.0.0.0.0.0.0 IN      PTR     host2.ipv6-rules.com.

DJBDNS configuration

There are currently some third-party patches available to the net-dns/djbdns package that allow it to do IPv6 name serving. DJBDNS can be installed with these patches by emerging it with ipv6 in the USE variable.

Warning
Not all record types are support yet with these patches. In particular, NS and MX records are not supported.
root #emerge --ask net-dns/djbdns

After djbdns is installed, it can be setup by running tinydns-setup and answering a few questions about which IP addresses to bind to, where to install tinydns, etc.

root #tinydns-setup

Assuming tinydns has been installed into /var/tinydns, edit /var/tinydns/root/data. This file will contain all the data needed to get tinydns handling DNS for the IPv6 delegation.

CODE sample data file
## (*.ipv6-rules.com is authoritatively handled by 192.168.0.1)
.ipv6-rules.com:192.168.0.1:a:259200
## (Authoritative reverse DNS for 2001:470:1f00:296::/64)
.6.9.2.0.0.0.f.1.0.7.4.0.1.0.0.2.ip6.arpa:192.168.0.1:a
## (Specify the IPs for host1 and host2)
6host1.ipv6-rules.com:200104701f0002960000000000000001:86400
6host2.ipv6-rules.com:200104701f0002960000000000000002:86400
## (Point www to host1)
3www.ipv6-rules.com:200104701f0002960000000000000002:86400

Lines prefixed with a 6 will have both an AAAA and a PTR record created. Those prefixed with a 3 will only have an AAAA record created. Besides manually editing the data file, it is possible to use the scripts add-host6 and add-alias6 to add new entries. After changes are made to the data file, simply run make from /var/tinydns/root. This will create /var/tinydns/root/data.cfb, which tinydns will use as its source of information for DNS requests.

IPv6 clients

Using radvd

Clients behind this router should now be able to connect to the rest of the net via IPv6. If using radvd, configuring hosts should be as easy as bringing the interface up. (This is probably already done by the net.ethX init scripts).

root #ip link set eth0 up
root #ip addr show eth0
1: eth0: <BROADCAST,MULTICAST,UP> mtu 1400 qdisc pfifo_fast qlen 1000
    link/ether 00:01:03:2f:27:89 brd ff:ff:ff:ff:ff:ff
    inet6 2001:470:1f00:296:209:6bff:fe06:b7b4/128 scope global
       valid_lft forever preferred_lft forever
    inet6 fe80::209:6bff:fe06:b7b4/64 scope link
       valid_lft forever preferred_lft forever
    inet6 ff02::1/128 scope global
       valid_lft forever preferred_lft forever

Should this not work ensure that the IPv6 firewall is allowing ICMPv6 packets through:

root #ip6tables -A INPUT -p icmpv6 -j ACCEPT

Troubleshooting

Package is missing IPv6 support

Packages will typically emerge with the ipv6 USE flag, but if IPv6 is not working on a specific program, checking that it is built with that is a good first step.

Note
There is no issue adding USE="ipv6" to /etc/portage/make.conf, but this is often unnecessary.
Note
Some packages (erroneously) detect IPv6 support automatically and hence have no ipv6 USE flag. Thus not all packages, which should support IPv6, will support it if they have not been compiled with an IPv6 enabled kernel.

See Also

External resources

There are many excellent resources online pertaining to IPv6.

On IRC, try the #ipv6 (webchat) channel on Libera.Chat. Connect to the Libera.Chat servers using an IPv6 enabled client by connecting to irc.ipv6.libera.chat.

This page is based on a document formerly found on our main website gentoo.org.
The following people contributed to the original document: Peter Johanson, Jorge Paulo, Camille Huot, Pasi Valminen, , Markos Chandras (Hwoarang)
They are listed here because wiki history does not allow for any external attribution. If you edit the wiki article, please do not add yourself here; your contributions are recorded on each article's associated history page.

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