Visitor
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3 Messages
No longer getting IPv6 address after Xfinity work in my neighborhood
I had a well working setup with IPv4 and IPv6. But there was some big work in my neighborhood today (got email about service interruption and saw several crews working on the street), and now that the work is completed, I now longer get an IPv6 address assigned. I didn't change any config on my side, and of course tried rebooting modem and router, still no IPv6.
Thanks,
Uwe
ub-net
Visitor
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3 Messages
3 years ago
Found the solution in another post: my router's firewall expects dhcpv6 to have a source address of fe80::/10. But after today's service changes in my neighborhood, that seems no longer true. If I allow arbitrary dhcpv6 source addresses, everything is working fine now :)
This was the post that sent me on the right track: https://forums.xfinity.com/conversations/your-home-network/ipv6-not-available-after-service-outage/626c8692ee0ef23e5262bcbb?commentId=626c8c88ff19c3627da4bb09&replyId=626c926dee0ef23e5262bd5c
Cheers,
Uwe
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BruceW
Gold Problem Solver
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26.3K Messages
3 years ago
Note that IPv6 addresses assigned by Comcast would never fall in that range, as it is reserved for link-local addresses, usually self-assigned. See https://en.wikipedia.org/wiki/Link-local_address. IPv6 interfaces normally have two addresses: a link-local address only used for communication on the local network, and a public address used for communication with devices on other networks, like the Internet.
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ub-net
Visitor
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3 Messages
3 years ago
Hi Bruce,
we are talking about different things here. You are talking about the leased address. The one that Comcast hands out to its customers. That one is indeed never link-local.
But I'm talking about the address of Comcast's dhcp server itself. You see, some routers seem to expect that the dhcp server replies from a source address in the fe80 subnet. That means those routers have default firewall rules to allow an inbound dhcp package only if its source address is in the fe80 range. Please note that the source address of the dhcp package is different from the leased address that is transported inside the package.
And it was the case until recently that Comcast's dhcp replies had a source address in the fe80 range, but that seems no longer true now. The problem can be fixed by loosening firewall rules to allow arbitrary dhcp servers. But I don't know whether this may introduce security concerns, if I basically allow anybody on the internet to send me a dhcp package.
Cheers,
Uwe
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