Comcast and Prefix Request


  • Banned

    I may be just confused about how its supposed to work, but I don't seem to be getting a /60 from Comcast.

    On the WAN, I have 60 next too "DHCPv6 Prefix Delegation size" and "Send IPv6 prefix hint" checked. In the logs I see

     Nov 3 11:54:54	dhcp6c	65303	IA_PD prefix: 2601:41:c480:f0::/60 pltime=345600 vltime=345600
    

    The LAN interface is set to track. But I only see "64" as the prefix.

    Am I missing something?


  • Banned

    Alright so I set a third interface up, and I'm getting close but different IP. So looks like I am getting the /60, just confused about how the prefix shows up. So I guess never mind!


  • LAYER 8 Netgate

    Interfaces get assigned a /64. Don't try to stray from that. Everything will break. Interfaces get a /64. Period. Not just in pfSense.

    A /60 gives you 16 /64s.

    Each track interface will have a different hex digit as the IPv6 Prefix ID.

    So they issued you 2601:41:c480:f0::/60

    If the prefix ID on the tracking interface is 1, that interface will be 2601:41:c480:f1::1/64.

    If the prefix ID on the tracking interface is c, that interface will be 2601:41:c480:fc::1/64.

    The prefix ID "fills in" the difference between the prefix delegation and the interface /64 - 4 bits for a /60.

    If you were delegated a /56, you would have 8 bits of prefixes, or 00 - ff (256)

    If you were delegated a /48 you would have 16 bits of prefixes or 0000 - ffff (65536).


  • Banned

    That's helpful, thanks. I guess I was confused between what an interface gets assigned and the prefix delegation I would be getting. Definitely makes sense that interfaces get /64s. But it would be nice if there was somewhere that showed that I was getting the prefix I was asking for.

    I figured that's what the prefix ID meant, but it wasn't entirely clear, so thanks for clarifying that.

    Now to send /64s to my Cisco router for my VLAN's via a /61. But that's a separate question.


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