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v6-gw-scripts

These are scripts to helpe people setup a v6 gateway on ISPs who hand out a v6 block. They have only been tested with Comcast. See https://www.phildev.net/phil/blog/?p=308 for all the gory details.

Setup

  • Update /etc/sysctl.conf to set:
net.ipv6.conf.$YOUR_EXTERNAL_INTERFACE.accept_ra=2
net.ipv6.conf.$YOUR_EXTERNAL_INTERFACE.forwarding=0

Replacing $YOUR_EXTERNAL_INTERFACE with your external interface.

RA Daemon

These scripts can now support dnsmasq or radvd

For radvd:

  • Install radvd on your gateway and create /etc/radvd.conf.tmpl (which these scripst will use to create radvd.conf) that looks like this:
interface __IFACE__
{
   AdvSendAdvert on;
   RDNSS 2001:4860:4860::8888 2001:4860:4860::8844 {};
   prefix __PREFIX__
   {
     AdvOnLink on;
     AdvAutonomous on;
   };
};

The scripts will update __PREFIX__ and __IFACE__ for you.

For dnsmasq:

  • Install dnsmasq and create /etc/dnsmasq.conf.tmpl (sample is included in the template - You need to set some params yourself)
    • The scripts will replace __INTERFACES__ and __PREFIXES__ for you.

Script Locations:

  • Drop dhclient-ipv6 into /etc/dhcp/dhclient-exit-hooks.d/
  • Drop 99-ipv6 into /etc/network/if-up.d/ (or your distribution's equivalent)
  • Drop ipv6_prefix_dhclient.conf in /etc and update it to accurately represent your setup.

Multiple prefix

We now support multiple prefixes. We assume you want one /64 per interface. If you add additional interfaces to the OTHER_IFACES variable in ipv6_prefix_dhclient.conf then additional prefixes will be requested, and one will be put on each interface. Radvd's configuration will be updated accordingly.

There are a few things to note about multiple prefix support:

  • Not all ISPs support requesting more than one. Comcast does, however.
  • If you request more than one, but are only getting one, it's because comcast remembers the type of request made with a given DUID and always returns an answer to that same type of request when given the same DUID. You can remove the DUID in your leases file to fix this.
  • DHCPv6 will associate an IAID with each prefix and, assuming you keep getting the same prefixes, those IAIDs will be consistent. Therefore dhclient-ipv6 will keep a mapping of interface we associate-to-IAID so we can always put the right prefix on the right interface. This mapping is kept in /var/lib/dhcp/dhclient-ipv6-mapping. I highly recommend not messing with the files in there.

Extra notes:

  • You need at least version 4.1.1-P1-17 of isc-dhcp-client
  • You need to allow UDP traffic to/from fe80::/10 and to port 546/from port 547 - unless you have nf_conntrack_dhcpv6 module available and use conntrack.