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IPV6 - Prefix Delegation Size

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IPV6 - Prefix Delegation Size

Hello,

 

I'm setting up IPV6 for my home network and by default, Comcast is assigning a 64-bit prefix delegation size, which allows only 1 subnet. I have multiple subnets at home and I want to add support for IPV6. According to the last post to this thread, it stated that Comcast no longer accepts hint for /60 prefixes.  I'm a residential internet customer, how do I get more than 1 subnet when using Comcast? 

 

https://forums.xfinity.com/t5/Your-Home-Network/Issues-getting-an-IPv6-Address/m-p/3331986#

 

Thank you

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Re: IPV6 - Prefix Delegation Size

I need a bigger prefix too. I have 5 different VLANs/subnets. So far I haven't been able to reach any human being at Comcast to help me out or confirm that we can no longer get a /60. I found this post on reddit that suggests restting your DUID. I haven't had a chance to test this yet but if you are running pfSense, I think you just change the DUID mode or modify the raw DUID.

https://www.reddit.com/r/ipv6/comments/3cb6n5/comcast_all_residential_ipv6_delegations_are/

If this works I will post back.

 

Oddly, I was able to request a /63 successfully giving me 2 delegations, but that doesn't get me IPv6 in my entire network.

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Re: IPV6 - Prefix Delegation Size

@Blah12341 I am happy to report that changing the DUID on my pfSense firewall did indeed let me acquire a /60 delegation as you can see from my pfSense logs.

 

Jul 11 15:14:50 home dhcp6c[91548]: IA_PD prefix: 2601:441:xxx:xxxx::/60 pltime=3600 vltime=3600
Jul 11 15:14:51 home dhcp6c[91548]: IA_PD prefix: 2601:441:xxx:xxxx::/60 pltime=3600 vltime=3600
Jul 11 15:14:51 home dhcp6c[91548]: create a prefix 2601:441:xxx:xxxx::/60 pltime=3600, vltime=3600

 

I think what happens is that Comcast gets locked on your DUID once you do a DHCPv6 request. By default, this will usually be a /64 delegation. Then if you try to increase the delegation size, it is a roll of the dice whether or not IP space is open adjacent to your exsisting delegation (plus taking in proper subnetting into account). In my case, I was able to get a /63 but no larger. But then I changed my DUID, completely disabled IPv6, rebooted pfSense. When it cam back up, I made sure to enable IPv6 with a /60 delegation hint and I got it.

 

So, EG's assertion on that other thread that Comcast only does a /64 is completely false. You just have to request a /60 from the very first time you enable IPv6 (per DUID).