Maximum DNS packet size?

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


In message <70279.1412020875 at server1.tristatelogic.com>, "Ronald F. Guilmette" 
writes:
> 
> 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]

Mark

> _______________________________________________
> Please visit https://lists.isc.org/mailman/listinfo/bind-users to unsubscribe
>  from this list
> 
> bind-users mailing list
> bind-users at lists.isc.org
> https://lists.isc.org/mailman/listinfo/bind-users
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org


More information about the bind-users mailing list