DNS maximum message size

Mark Andrews marka at isc.org
Wed Aug 26 12:07:53 UTC 2009

In message <c923553c0908260234q46fef3d4g2591d8ef3a5324ea at mail.gmail.com>, Luis 
Silva writes:
> Hi,
> Can anyone tell me the maximum size for DNS messages using TCP? I scanned
> all RFCs that I knew, but I can't find the answer. The problem is that I'm
> integrating my BIND server with a DNS name server which can only send AXFR
> answers with a 65535 maximum message size.
> Thank you,
> LS

	DNS messages over TCP are limited to 65535 bytes due to
	there being only two bytes to encode the length in.

Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org

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