[j-nsp] FBF and fragmented UDP packets

[Niels Bakker]

* peter at devries.tv (peter at devries.tv) [Fri 27 Feb 2004, 04:30 CET]:
> Kind of a tough problem here.  We're strictly using FBF and static
> routes (routing instances) to route packets through a M20 (M40 in
> production) the issue that we have is that we need to send fragmented
> UDP packets to the same routing instance as their initial packet, but 
> only fragmented UDP packets that are DNS without catching every other
> fragmented UDP packet.  

You're in luck: UDP DNS packets can't get over 512 bytes!  (See RFC1035,
section 2.3.4; nameservers fall back to TCP if the answer to a query
exceeds this limit.)

In other words, you're unlikely to see a fragmented UDP packet that's
part of a valid DNS query, unless you have links with an MTU smaller
than 576 bytes in your network.


	-- Niels.

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