[dns-operations] Any surveys about EDNS0 usage?
mgraff at isc.org
Mon Mar 7 22:24:50 UTC 2011
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My take on this is that it's very hard to measure. It's very easy to
tell if someone allows TCP, but EDNS0 support, unless specifically
queried for and then done carefully, seems hard to measure.
One problem that will happen more and more is that EDNS0 is in the
software, but some firewall will prevent fragments, > 512 UDP on port
53, or filter out OPT records. So, is this a server that supports EDNS0
Every day we run into the problem that a remote server will announce
that it accepts a size of 4096 in its query, and the remote end fully
supports EDNS0 in their server. It will reply with a reasonable but >
512 byte reply, sometimes without fragmentation (say, around 600 bytes)
but *something* eats the reply. It is very hard to work in this
environment as a recursive server as the fallbacks add up fast.
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