Comcast Native IPv6 with multi LAN's

  • I was wondering if it was possible to do some sort of subnetting on on the /64 I am getting from Comcast. I have multiple LAN's I would like to start using IPv6 but I'm not sure how to get more then one LAN interface to hand out IPv6 addresses.

  • If you are using all static addresses then technically you can use whatever subnet mask you want on your LAN side to split your /64 allocation, although this will break DHCP/ND as it requires all 64 bits of the suffix per network for ND to work. Generally if you're planning to use IPv6 on more than one network you'd get a /56 or a /48 from your provider.

  • does anyone know if it's possible to get a /56 or a /48 from Comcast?

  • Not currently although one of the users managed to request 2 /64 prefix delegations, which worked.

    There is no GUI for this and required changes in the /var/etc/dhcp6c_{interface}.conf
    Per default there is only a request for pd0. If you add a similar statement for pd1 you can assign that to another interface.

    You can not sensibly split up the /64 as the prevents auto config from working.

  • Who don't providers hand out a minimum of a /56? It will just be more overhead for them when people want more than a signle subnet and its not like they don't have the space…...

  • So apparently Comcast will not give out prefixes up to /60 if requested by the DHCP6 client on the router:

  • Having said that, I can't seem to get this to work with the 2.1 snapshot from Apr 2: When I select a prefix size shorter than /64, I can see the sla-len field in the prefix-interface entry for the LAN interface get updated accordingly, but it looks like no prefix-interface entries are created for additional interfaces that I tell to track WAN (with prefix IDs greater than zero). Is this expected to work?

  • Never mind, rebooted the router and now the entry for my second interface shows up as expected.

    I also just read elsewhere that Comcast have temporarily suspended support for requesting prefixes shorter than /64.