[dns-operations] Strange problem with fragmented DNS responses from b.iana-servers.net

Simon Leinen simon.leinen at switch.ch
Wed Dec 10 16:00:16 UTC 2008

Ray Bellis writes:

> As I was running the ISP side of the network at the time I was able
> to verify that the fragments were going to the WAN side of the
> router in the wrong order, and weren't coming out on the LAN side.

Please don't say "wrong".  I don't think it is specified anywhere in
which order fragments should be sent, and at any rate an IP network
may always reorder packets (including fragments).  So every
IP-speaking device that reassembles packets MUST be prepared to
receive fragments in an order different from ascending-byte-count.

(It is actually somewhat *easier* for the reassembler if the last
fragment arrives first, because that fragment contains the information
of how big a buffer is needed for the entire packet.  I believe this
was the reasoning why (some versions of) the Linux kernel decided to
send fragments out like that.)

Anyway, this doesn't seem to be the problem here - the padding issue
looks more suspicious to me.

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