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Hi,

I run a dhcpv6 server (package dhcp-server-4.3.6-20.fc28.x86_64 from
fedora, kernel 4.17.*) for the purpose of delegating prefixes to my
wifi network (Google wifi).  This worked fine until I added an
interface alias on the server in order to add an additional ipv4
address; the server then failed to respond to SOLICIT packets.

As the alias has no ipv6 address (for v6, the kernel keeps all the
details with the parent interface and ignores aliases), the dhcp
server ignores incoming requests if they are thought to have come in
on the alias.  Unfortunately, the pktinfo data attached to the packets
identifies the alias as the incoming interface.

See attached patch for a suggested fix that was verified to work on my
network.  If the interface identified by the pktinfo data is an alias,
find the parent interface and use that instead.

Note that independently of this workaround, it is possibly something
that should be fixed in the kernel, as it doesn't seem right to
identify an interface that doesn't have an ipv6 interface as the
source of packets.

Thanks,
Marc