[dns-operations] latest bind, EDNS & TCP

Simon Munton Simon.Munton at cdns.net
Sat Oct 11 09:33:10 UTC 2014

> that bind will fall back to resend the query with EDNS size=512 if it does not get an answer

We are replying to every UDP query, but the query is immediately 
re-issued over TCP - if the reply was lost, I'd expect a delay.

The fact its immediately re-issued over TCP suggests (to me) this is in 
response to TC=1.

My big concern is if this is an issue in a new release of bind, while 
people stick with an old version we are OK, but then there could be a 
tidal wave of TCP/DNS approaching us all as people upgrade.

If we see this come and can do something about it first that would be a 
better result than waiting to be swamped.

As far as the actual TCP traffic levels go right now, they are of little 
or no consequence.

But its unusual and surprising for TCP traffic to have suddenly increased.

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