[atlas] Request to test TCP and UDP to the root servers separately.

philip.homburg at ripe.net:
> The probes are already measuring this. I don't think we made any
> graphs of the results.

Do you also measure whether the path to root servers (other DNS
servers?) allow for fragmented UDP packets? If you announce an EDNS(0)
buffer size of 4K and ask for some DNSSEC related records, you often
receive fragmented UDP messages. It would be interesting to see whether
those fragments make it back to the client. If not, there will be
timeouts and TCP resends, which I call bad (YMMV). The query produced by
the command

    dig @X.root-servers.net . ANY +dnssec

ticles the root servers to send a 3966-byte message, which triggers
interesting behaviour in my neck of the woods - such as fragment
reordering and consequential reassembly failure - so it's important to
not only look at the IP result of the query, but to actually look at the
arriving packets.

Just a thought ...

				Cheers,
				  /Lars-Johan Liman
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