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IPV6 DHCP-PD hints with Xfinity working?


IPV6 DHCP-PD hints with Xfinity working?



Have done a few experiments to get IPV6 prefixes from Comcast for my internal network using DHCP-PD.


1 - I noticed that if I send a hint requesting a /60, I only get a /64.  However, if I send a hint for /56, I get the /60.  Is this by design?

2 - I noticed that if I give a hint for the for /60 prefix... i.e. 2601:XXX:XXXX:XXX0::/60 (X replaces the real numbers for privacy here), it's fully ignored.  I would like to get the prefixes back that I normally use, but they change on every reboot of my router.  Does Xfinity ignore my prefix request?  It kind of doesn't make sense for me to use internal IPV6 /64s if I can't somewhat get some stability in getting my prefixes back as not everything internally can use SLAAC.

3 - Because of #2 above, I noticed that if my router reboots and it gets a new set of IPV6 prefixes, I am forced to reboot my modem as it won't pass the traffic unless I do that.  This needs to happen everytime.  Is this ALSO by design?  I don't need to do this for IPv4.


Thanks in advance for some answers :-)


Re: IPV6 DHCP-PD hints with Xfinity working?

I saw a post on Reddit where John Brzozowski (ComcastJohn - the IP6 guy at Comcast) stated that if you want a /60, request a /56:


He stated:

Regarding the /60 it sounds like your cable modem is operating as a bridge and your ASA is the router requesting IPv6 from Comcast. Is this accurate? If yes, and your ASA previously requested and received the default prefix length (/64) our DHCP infrastructure will continue to renew that unless certain conditions are met. A quick fix you can try is

    * Make sure your hint is configured to be a /56
    * Reset or change your DUID
    * Reboot the ASA or restart the DHCPv6 client process

NOTE - this will result in a delegated prefix change

PS - I lead IPv6 at Comcast Smiley Wink

If this indeed true?  I need to ask for a /56 to get a /60?  Is this a workaround to prevent the ability to ask for a particular address prefix since asking for a /60 will never result in a /60?