SOLVED: IPv6 with Comcast Business: Router Advertisement Questions

[TrustedComputer]

I have Comcast Business as my ISP and have a Cisco 3941B Business Gateway. I am running OPNsense 18.7.9 behind it and have recently got IPv6 running (mostly) but I'm having trouble with getting Router Advertisements working with the "Track Interface" setting on the LAN interface of OPNsense.

I did a lot of searching, but none of the guides out there worked for me. Through trial and error, the combination of settings I used to get basic routing functionality were this: Comcast Business Gateway set to Stateful (Use DHCP Server), along with using DHCPv6 on the WAN interface of my OPNsense appliance with 64 bits for the prefix delegation size, which is confusing since the Comcast Business Gateway says I have a delegated /56, but this is the only way I can get it to work. Then I used WAN interface Tracking on the LAN Interface with Prefix ID 0.

With all this set, under Interfaces---Overview, I have a modified EUI-64 auto-configured IPv6 address with a /64 prefix length on my OPNsense WAN interface (not a DHCP IPv6 address). My OPNsense LAN address gets auto-configured with a modified EUI-64 IPv6 address and a /59 prefix, which seems strange (once again) since my Comcast Business Gateway says I have a delegated /56.

Then, if I manually configure my hosts sitting behind the OPNsense appliance with appropriate IPv6 addresses in the same subnet as the OPNsense LAN interface and use its address as the default gateway, then routing works and I am able to get IPv6 internet access with my hosts. So this is a big success!

However, I can't figure out how to get my router advertisements working properly with the above configuration, which would allow me to use automatic configuration for my LAN hosts. SLAAC only seems to work if I manually configure my OPNsense LAN interface's IPv6 address with the one it would have gotten from "Track Interface" and to use a /64 prefix length. My Router Advertisement settings are set to "Stateless", "Normal" router priority, "Advertise Default Gateway" checked, and "RA Sending" checked.

How can I get SLAAC for LAN hosts working along with "Track Interface" on the LAN interface of my OPNsense appliance?

[marjohn56]

So you have the comcast gateway before it gets to the Opnsense router?


 If that is the case then it could be that the /56 is allocated to that router. Any subsequent routers will get a smaller allocation.


Simplest method is to set ipv6 on WAN, select prevent release and directly send solicit. On the LAN set track interface, Track IPv6 interface is WAN and the prefix ID left at 0.


Do NOT select manual configuration. Everything is then on automatic and it should just work.

[TrustedComputer]

Thanks! This did the trick. I also need to set the prefix length on the WAN interface to /59, but now Track Interface works as well as internal host SLAAC!