[Pdns-users] MSG SIZE exceeds 512 bytes

Peter van Dijk peter.van.dijk at netherlabs.nl
Wed Dec 5 13:16:14 UTC 2012

Hello Winfried,

On Dec 5, 2012, at 10:07 , abang wrote:

> I wonder how can a answer packet from our PowerDNS Recursor (3.4-pre) exceeds 512 bytes. I thought this is the limit and it should be truncated. The MSG SIZE in the example below is 701. Has someone a explanation for this?

dig, by default, sends an EDNS bufsize with a request (4096 bytes in the version I tested), allowing the server to go beyond 512 bytes. If you add +noedns or +bufsize=512, you should see a truncated answer (although, if additionals are the reason, the TC-flag will not be set).

HOWEVER, if the packet cache is enabled, and the query that caused a packet cache entry happened to have EDNS, non-EDNS clients coming in after that will also get the big answer. I will write a ticket about this.

Kind regards,
Peter van Dijk
Netherlabs Computer Consulting BV - http://www.netherlabs.nl/

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