Subnetting the /56 on DPC3941B

Question

Has anyone been able to successfully subnet the /56 assignment? On the DPC3941B, the LAN is configured with a /64 that I cannot change. The gateway doesn't support static IPv6 routes so I can't use the other subnets on a downstream router.

I've opened three tickets with Comcast Business but I can't seem to get them past the "Comcast doesn't support IPv6" canned response.

Is there a config or at least a phone number for Comcast that does understand how to deal with IPv6?

Thanks!

ndb217 · Accepted Answer

I've made some headway on this. According to tier 2 the cisco does support a prefix delegation in passthrough mode, although mine is apparently problematic so it's being replaced with the netgear. I know that the netgear will work when you request a prefix delegation - my old one hands me a /60. According to the tech the Cisco gateway should also do this. I'm not clear if you can use the entire /56, even statically. If you don't need more than the 100Mb package you could ask for a netgear, I know those work.

MagellanTX · Accepted Answer

Update: Comcast came out and replaced the Cisco for a Netgear CG3000DCR. As ndb217 stated, It's broadcasting a /60 so that might be a problem later (I need x2 /57) but at least the routing is working now.

MagellanTX · Answer

Thank you for the information.

Mine is in passthrough mode and PD is mostly working (can't get anything larger than /59) but I can live without PD. I wondering if it's the routing that's messed up.

If I plug a PC directly into the gateway and use an address off the gateway's /64 then everything works.

My absolute largest problem though is getting someone from Comcast who's willing to help me. I can't even get past level 1 support - They keep telling me that IPv6 is not supported even though my business portal and router show that it's assigned.

MagellanTX

Subnetting the /56 on DPC3941B

ndb217

MagellanTX

MagellanTX