[lwip-devel] [bug #49134] mDNS should not advertise invalid IPv4 address

[Daniel Elstner]

Follow-up Comment #2, bug #49134 (project lwip):

Good question. I checked the DHCP code and it does reset the IP to 0.0.0.0 on
nak/release, so that part is fine.

Skimming through RFC 6762 now. I'm totally new to all this so please bear with
me:

It seems that the way it is supposed to work is that a newly announced A
record for the same hostname (or PTR record for the same IP), with the
cash-flush bit set, would immediately replace any stale record. This is
regardless of who sends it, so if someone else takes over an IP previously
used by another host, then that would just work.

However, I can't find any explicit means to flush a cache entry without at the
same time providing a replacement. There are some hints though that simply
sending the record again with TTL set to 1 second should essentially do the
trick.

Not sure if it is worth it to implement that in lwIP. The most common reason
for losing a DHCP lease is probably a (temporary) disconnect; in which case we
cannot send anything anyway. Also, any stale mDNS record would be flushed
anyway as soon as a new lease is obtained after reconnection.

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