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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 :-)
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:
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
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?