IPv6 Setup for Comcast on WRT3200ACM

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Pastorbrendad
DD-WRT Novice


Joined: 18 Apr 2019
Posts: 29

PostPosted: Sun Apr 03, 2022 1:14    Post subject: IPv6 Setup for Comcast on WRT3200ACM Reply with quote
Router: WRT3200ACM
Firmware: 48567

I'm trying to get IPv6 set up on my router. A while back I had it working, but I think Comcast changed something on their end, and I haven't been able to configure my router properly for IPv6 since. I've tried different builds, clearing the nvram, and every configuration I could find scouring this forum, google, etc.

With my current configuration, dd-wrt is showing an IPv6 address in the top right corner of the GUI, my client devices are getting IPv6 addresses, and I can ping6 other clients on the LAN, but test-ipv6 is failing. Here's some info about my configuration: please let me know if you need more info to help.

Modem: Comcast modem/router combo in bridge mode (With bridge mode off, I am able to get a working IPv6 connection through the Xfinity router)

Operating Mode: Gateway

Connection Type: Auto Config - DHCP
Ignore WAN DNS: disabled
Use VLAN Priority: disabled

Gateway, Local DNS, and Static DNSs are all left at 0.0.0.0

DHCP Type: Server
Use DNSMasq for DNS: Enabled
DHCP-Authoritative: Enabled
Recursive DNS Resolving (Unbound): Disabled
Forced DNS Redirection: Disabled

IPv6: Enable
Type: DHCPv6 with Prefix Delegation
Prefix Length: 64
Static DNS 1,2: Left Blank
MTU: 1500
No release on reconnect: Disabled
Dhcp6c custom: Disabled
Dhcp6s: Enabled
Sequential IPs: Disabled
Dhcp6s custom: Disabled
Radvd: Enabled
Radvd custom: Disabled

DHCP Server
Used Domain: LAN and WLAN

Dnsmasq: Enabled
Encrypt DNS: Disabled
Cache DNSSEC data: Enabled
Validate DNS Replies (DNSSEC): Enabled
Check unsigned DNS replies: Enabled
No DNS Rebind: Enabled
Query DNS in Strict Order: Disabled
Add Requestor MAC to DNS Query: Enabled
RFC4039 Rapid Commit support: Disabled

Thanks to anyone who is able to help!
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Per Yngve Berg
DD-WRT Guru


Joined: 13 Aug 2013
Posts: 6532
Location: Romerike, Norway

PostPosted: Sun Apr 03, 2022 10:46    Post subject: Reply with quote
You get an IPv6 network that starts with 2xxx:?

Try a traceroute6 2620:fe::9 and see where it stops.

If you run Windows the command is "tracert"
the-joker
DD-WRT Developer/Maintainer


Joined: 31 Jul 2021
Posts: 1837
Location: All over YOUR webs

PostPosted: Sun Apr 03, 2022 11:07    Post subject: Reply with quote
Also is your ISP using Type: DHCPv6 with Prefix Delegation or another type? I would try match their service/setup in DD-WRT
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Router: ANus RT-AC68U E1 (recognized as C1)
Per Yngve Berg
DD-WRT Guru


Joined: 13 Aug 2013
Posts: 6532
Location: Romerike, Norway

PostPosted: Sun Apr 03, 2022 12:04    Post subject: Reply with quote
Comcast should also give you a /56 prefix length if you want more than one sub-net on your lan.
Pastorbrendad
DD-WRT Novice


Joined: 18 Apr 2019
Posts: 29

PostPosted: Sun Apr 03, 2022 13:23    Post subject: Reply with quote
Per Yngve Berg wrote:
You get an IPv6 network that starts with 2xxx:?

Try a traceroute6 2620:fe::9 and see where it stops.

If you run Windows the command is "tracert"



Yes, it does.

Ran traceroute: It stops at the IPv6 address that's assigned to my router. I'm guessing that means my LAN is setup as IPv6, but that doesn't match what's being issued by Comcast? No clue how to fix that lol.

(Also, for anyone who is following along in the future, the command in terminal is traceroute6 if you're on a Mac.)
Pastorbrendad
DD-WRT Novice


Joined: 18 Apr 2019
Posts: 29

PostPosted: Sun Apr 03, 2022 13:37    Post subject: Reply with quote
the-joker wrote:
Also is your ISP using Type: DHCPv6 with Prefix Delegation or another type? I would try match their service/setup in DD-WRT


Everything I've been able to find in the forums says people had success with Comcast/Xfinity using Prefix Delegation.

Stupid question: what's the best way to find out what they're using? Their customer support is atrocious. Should I take their modem/router out of bridge mode, and see what it's configuration says?
the-joker
DD-WRT Developer/Maintainer


Joined: 31 Jul 2021
Posts: 1837
Location: All over YOUR webs

PostPosted: Sun Apr 03, 2022 16:21    Post subject: Reply with quote
Or look at what their router says.

Also a good test is ping an outside network from anywhere behind dd-wrt as is.

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Router: ANus RT-AC68U E1 (recognized as C1)
Oldsmobile_Mike
DD-WRT Novice


Joined: 02 Jul 2014
Posts: 43

PostPosted: Sat Apr 16, 2022 7:28    Post subject: Reply with quote
Try this guide. I had mine working a while ago, then it stopped working. Did the steps listed here and IPv6 is working again. May work for you?

https://sites.google.com/view/chewkeanho/guides/dd-wrt/setup-dhcpv6-with-prefix-delegations?authuser=0
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