[dns-operations] Link-local IP addresses for a resolver?

Tony Finch dot at dotat.at
Wed Sep 25 10:55:29 UTC 2019

John Levine <johnl at taugh.com> wrote:
> How are they with RFC 4193 ULAs?  I've been using a cache at a ULA on
> my two-segment home network and it seems to work fine.

I would expect them to "just work" modulo the network connectivity issues
associated with ULAs mentioned by Mark.

The problem with link-local addresses is "which link?" so to answer that
the resolver address has to be scoped. When I looked, the common problem
was to store the resolver address as 16 bare bytes which lacks space for
the interface scope, rather than sockaddr_in6 which includes the scope and
other complications. That's if the code parsed and ignored the scope; it
was also common to simply fail to parse the scoped address.

I also have vague worries about lurking bugs with RDNSS and DHCPv6
resolver configuration: the addresses on the wire are bare and only
implicitly scoped to the interface they arrived on, which offers so many
opportunities to make mistakes.

f.anthony.n.finch  <dot at dotat.at>  http://dotat.at/
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