IPv6 on Comcast

Post new topic   Reply to topic    DD-WRT Forum Forum Index -> Advanced Networking
Author Message
DD-WRT Novice

Joined: 03 Oct 2016
Posts: 1

PostPosted: Mon Oct 03, 2016 17:21    Post subject: IPv6 on Comcast Reply with quote
Hey! I'm pretty sure this isn't really an "Advanced Networking" questions, but I couldn't find a a better matching board.

I'm trying to get an IPv6 connection on my home network and I couldn't find a solution for days. Here is what I got so far:

When I plug my MacBook directly into the modem I get a IPv6 IP and connection and everything seems to work just fine (test-ipv6 is happy).
When I plug in my old AirPort Express it thinks it gets a IPv6 connection, but the values don't seem to be right: Default Gateway is sometimes ::1. Sometimes I get an IP and gateway that look like they could make sense, but my IPv6 connections always time out. When I enable an 6to4 tunnel on the APE it will seem to work but coonections seem to fail kind of randomly when I try to rely on a IPv6 connection.

On my dd-wrt router I tried IPv6 with PRefix Delegation, I tried Dhcp6s, I tried Radvd. I wouldn't get an IPv6 address in any of these configurations.
Per Yngve Berg

Joined: 13 Aug 2013
Posts: 5799
Location: Romerike, Norway

PostPosted: Fri Oct 07, 2016 10:00    Post subject: Reply with quote
I believe IPv6 with PRefix Delegation with a len=56 is correct for Comcast.

Joined: 24 Aug 2012
Posts: 223

PostPosted: Sun Oct 30, 2016 2:30    Post subject: Reply with quote
Comcast will take a variety of prefixes. The default PD is 64; the Macbook is probably getting a 128-bit NA rather than a PD. Try these settings in DD-WRT's Setup->IPv6 tab to get a working configuration:

DHCPv6 with Prefix Delegation
Prefix length 64
MTU 1500

Dhcp6c custom disabled
Dhcp6s custom disabled

On the Setup->Basic tab, if you checkmarked Use DNSmasq for DHCP, you may need to setup the IPv6 address ranges. In my Services tab under Additional DNSmasq options, I tell DNSmasq where to get the IPv6 ranges:

The PD is tied to the WAN MAC, and Comcast has 7-day PD leases. To change my PD to 60 for subnetting, I had to change the prefix length to 60 and clone the MAC off an old router. Alternatively I could have changed the prefix and switched off IPv6 for a week.

[Broadcom] Asus rt-ac66u r35531 ('66 should only be factory reset through the DD UI)
Fix RT-AC66U "wl1 [2.4 GHz TurboQAM]". DD-WRT failsafe UI @ http|

Joined: 20 Apr 2010
Posts: 203

PostPosted: Wed May 23, 2018 20:04    Post subject: Reply with quote
Just wanted to say thank you, been trying to figure out how to get ipv6 working for a while now on comcast and i followed this advice. I didnt have to change any advanced options just the stuff under setup --> ipv6 once i changed that i checked on ipv6test.com and its all green now.
Display posts from previous:    Page 1 of 1
Post new topic   Reply to topic    DD-WRT Forum Forum Index -> Advanced Networking All times are GMT


Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You cannot download files in this forum