port 53 tcp/udp

Mark Andrews marka at isc.org
Tue Jul 17 21:43:34 UTC 2012

In message <20120717194840.GA3773 at glasya2>, nex6 writes:
> when does bind or dns in general use tcp and when does it use udp?

When it needs to.  TCP support is NOT optional.
> from what i have read, from the client intial request if under 512b
> come in on UDP port 53, if and depending on the local
> resolver in needs to retry it *could* be a tcp port 53 request?
> now thats client to name server;
> what about, recursive lookups? or forwarded requests? etc 

It's still client to server.  Recursive servers have a client side
and a server side.

> how does that work?

Exactly the same why.
> -Nex6
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Mark Andrews, ISC
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