Re: [dnssd] Adoption call for draft-sctl-advertising-proxy

[Ted Lemon <[e-mail]>]

On August 13, 2021 at 1:49:37 PM, Jonathan Hui ([e-mail]) wrote:

On Wi-Fi, the device needs to discover the SRP server. Why can't
dnssd-zone-discover help with that? If there is a single SRP server in the
network and it is servicing both Wi-Fi and Thread networks, we don't need
to deal with conflicts. If there are multiple SRP servers, then I hope SRP
replication will address the vast majority of cases.

dnssd-zone-discover lets you discover DNSSD zones that you can browse. It
doesn't tell you about the SRP server. We need a different DNSSD
advertisement for that. Not a big deal.


> > The only other alternative is to rename. I think this is too heavy of a
>
> > solution, but I'm open to debate.
>
> It increases the complexity on every device that needs to browse for
> mDNS services. I would prefer SRP replication to renaming.
>
> This is a good point—SRP replication also increases complexity, but it
> constrains it nicely to the more capable nodes on the network—the ones that
> are acting as ad-hoc infrastructure and not as end nodes.
>
I hope SRP replication will eliminate the need for end devices to handle
conflicts directly. Hopefully we can get some operational experience as to
whether other mitigations are necessary.

Yes. Well, FWIW, my current code does both SRP replication _and_ doesn't
defend names, so we may be getting operational experience on both. :)

Another thing to be aware of is that because of the way mDNS works, if you
are using mDNS for discovery, a name conflict when names aren't being
defended will sit around in the cache for a few minutes. If names are
defended, this doesn't happen; one alternative is to just defend names and
count on SRP to deal with conflicts, but the downside of this is that now
there is a delay before the new information appears.

This delay could potentially be minimized by retrying to register as soon
as the SRP replication update has been acknowledged by all SRP replication
peers—right now my code (when name defense is enabled) just waits two
minutes before re-attempting, which is a lot longer than should be
necessary.