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Re: [lwip-devel] Question regarding MDNS defending name.

From: Jens Nielsen
Subject: Re: [lwip-devel] Question regarding MDNS defending name.
Date: Tue, 27 Mar 2018 19:53:09 +0200
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Nice to hear more work is being pitched into mDNS :)  Did you also intend to post your work back to lwip?

As far as I know...
However, after some time, it receives a packet whose contents indicates that
it's name/service are in conflict.
This would be another node sending a response or announce with our name/service but different rdata, right?

 From the RFC 6762, Section 9, the immediate action would be to return to
PROBING. However, I am confused, bcz at this stage, since the node have
already confirmed its records being unique, it should instead send a
RESPONSE rather than restart the probing as suggested
But since the conflict packet is a response/announce you can't send a response to that? Just because probing is completed doesn't mean it's 100% guaranteed to be unique, maybe a switch was down so both nodes passed probing on each part of the network? Going back to probing seems like an appropriate action to me, I recall the other mDNS implementation I was testing against did that when my probing implementation misbehaved and I announced a name that was already in use...

, and it's in
contradiction with Section 8.1
"*In order to allow services to announce their presence without
    unreasonable delay, the time window for probing is intentionally set
    quite short.  As a result of this, from the time the first probe
    packet is sent, another device on the network using that name has
    just 750 ms to respond to defend its name.*"
I'm not sure I understand the contradiction? That part is about not delaying a response to a probe (as it should when responding to normal queries, as described in Section 6)

Btw, just to make sure we aren't doing the same thing, you're aware there are a set of patches for probing on savannah here? https://savannah.nongnu.org/patch/?9555

Best regards

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