[Pdns-users] Length of TXT records

Peter van Dijk peter.van.dijk at netherlabs.nl
Wed Oct 17 07:47:11 UTC 2012

Hello Jörg,

On Oct 17, 2012, at 9:35 , Joerg Stephan wrote:

> we use PDNS in our nameserverset for customer domains. Currently we have a request by a customer to provide TXT records with more than 255 chars. We use a MySQL backend an thought about just increasing the VARCHAR. But that seems to be a problem caused by UDP package size and the fact that PDNS does not support this. Am i right? Or is there any way of workaround to this issue.

The current recommendation (assuming MySQL 5.1 or up) for the content field is VARCHAR(64000).

TXT records, in DNS, consist of one or more sections, each up to 255 bytes long. However, PowerDNS supports putting longer strings in the database, and will auto split them for you.

UDP packet size is limited to 512 bytes unless a client reports a bigger bufsize via EDNS. In either case, if the response is too big, PowerDNS will send a truncated response, informing the client that it should re-query over TCP.

In short, you should have no problems increasing your content VARCHAR size and inserting your bigger TXT records.

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

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