Maximum DNS packet size?

Mark Andrews marka at
Mon Sep 29 21:40:54 UTC 2014

In message <70279.1412020875 at>, "Ronald F. Guilmette" 
> My apologies if this question might also be considered a bit
> off-topic for this list.
> Is the maximum possible size of a DNS packet (just the payload part...
> not including IP and UDP headers) 64k bytes?
> I have some old code which assumes that, perhaps incorrectly.

DNS UDP message size can be up to 512 bytes. RFC 103[45]

EDNS UDP message size can be up to 65535 bytes less overhead but
most implementations advertise a much smaller size (~4K). RFC 6891

TCP message size can be up to 65535 bytes as there is a 2 octet header
specifying the size of the TCP DNS message. RFC 103[45]


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Mark Andrews, ISC
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