[davesimplii]

Help! I can't get this thing to work with the carrier ipv6 routing. I can get it to route from the tp-link, but I can't get it to route from a PC on the LAN. I'm not even sure it is giving out the correct LAN IPv6 addressing to the client PC. I've tried this tp-link in default firmware mode and added dd-wrt firmware to get it to try something else, but both ways act the same. I'm new to ipv6 and really don't know what I am doing. Can you offer some real setup instructions as the grok.com and google searches just lead me in circles. I have version dd-wrt v3.0-r61981 std (07/29/2025) firmware on it currently. Any assistance is much appreciated. Thanks.

[egc]

Moved this to the Advanced Networking forum

Does your ISP router has IPv6?

Is your ISP handing out an IPv6 Prefix Delegation (PD)?
If so what size, you need at least a /56 or lower (e.g. /48 ) PD.

Can your ISP modem/router be set in bridge mode so that your router is directly connected to the internet e.g. does it have a public IP address?
If not can it delegate a prefix to other routers?

[davesimplii]

Yes the ISP has IPv6.
It is supposed to be handing out IPv6 Prefix Delegation as they gave us the prefix of 2603:3026:541:D400::/56 (I changed a few digits to protect our network).
The ISP modem is from Comcast and there are several things online stating that you shouldn't bridge the modem. Plus in the past if you bridge a Comcast modem, then it breaks the IPv4 and kills the modem. We do have a static IPv4 address range on it though of /29.

Currently it gives the router, behind the Comcast modem, an IPv6 address, but doesn't seem to want to route from the LAN to the WAN. I'm not sure if it's handing out proper IPv6 addressing to the PC clients.

[davesimplii]

The Comcast modem WAN IPv6 parameters shows this:
WAN IP Address (IPv6): 2001:558:6008:4b:2ca8:cb79:707:3bce
WAN Default Gateway Address (IPv6): fe80::21c:56ff:fe00:99
Delegated prefix (IPv6): 2603:3026:541:d400::/56
WAN Link Local Address (IPv6): fe80::c64f:86ff:feb9:a8f0
Plus appropriate DNS addresses for IPv6.
The Comcast modem LAN IPv6 parameters shows this:
Link-Local Gateway Address: fe80:0:0:0:c64f:86ff:feb9:a8f1
Global Gateway Address: 2603:3026:541:d400:c64f:86ff:feb9:a8f1
Stateless (Auto-Config), but we've tried the Stateful (Use DHCP Server) as well with no differences.
DHCPv6 Beginning Address: 2603:3026:541:d400:0:0:0:0001/64
DHCPv6 Ending Address: 2603:3026:541:d400:0:0:0:fffe/64

The DD-WRT TP-Link Archer C7 v2 gets a WAN IPv6 address of 2603:3026:541:d400:1ad6:c7ff:fe6d:81d8 from the Comcast Modem.
The Windows PC behind the TP-Link is getting the following IPv6 parameters:
IPv6 Address: 2603:3026:541:d400:434:6245:b9bc:f763
Temporary IPv6 Address: 2603:3026:541:d400:997e:f72a:3969:20f1
Link-local IPv6 Address: fe80:dda:4ef:52a5:5477%8
Default Gateway: fe80::1ad7:d3ff:fe6d:81d8%8

(I've changed a few of the numbers to protect our network, but the patterns should be the same)

[egc]

Ok but does the Comcast router hands out a prefix to a downstream router if asked?
Usually this is not the case or if you are lucky it will hand out a /64 prefix (which might be sufficient in your case).

But without a delegated prefix you can not setup IPv6 (DDWRT does not support IPv6 relay)

If you have a prefix delegated setup is fairly easy:
https://raw.githubusercontent.com/egc112/ddwrt/main/IPv6%20DNSMasq%20IPv6%20RA.pdf

[davesimplii]

Does my last post tell you if the Comcast modem is handing out the prefix, or not? I have no idea how to check that it is.

[davesimplii]

I just tried your DNSMasq document and it doesn't change anything, except now the PC doesn't have any of the IPv6 stuff on it except a local-link ipv6 address that doesn't help at all. Did you see my addressing post that lays things out?

[egc]

[davesimplii]

Isn't that what this is?

[davesimplii]

Or this?

[davesimplii]

Comcast support is next to useless.

[egc]

That is the prefix the comcast router gets delegated but it does not tell if it will also have an DHCPv6 server which delegate prefixes.

If you setup the DDWRT with e.g. a request for a delegated prefix of 64 and it is not working chances are the comcast does not delegate a prefix but I do not have comcast so I do not know, I do have a cable modem from vodafone and have put that in bridge mode with full dual stack and a public IPv4 address