RRSet size limitation lower than predicted by RDLENGTH field size

Mark Andrews Mark_Andrews at isc.org
Fri Apr 25 06:37:09 UTC 2008


> We're pushing the limits of RRSet sizes for A records in the responses to
> queries for our lists, but we're finding that the practical limit is much
> lower than that predicted in the binary message format specs.
>  
> The octets in the RDLENGTH param (16 bit unsigned = 65535) should allow
> 16384 A records in a single RRSET using TCP, but the behavior we are
> observing in BIND is a limitation of 4096 A records.
>  
> We're using Bind 9.4.1-P1 on Gentoo.
>  
> Any ideas what's causing this, or how to fix it?


	Each A record takes 16 octets.

	2 for the name
	2 for the type
	2 for the class
	4 for the ttl
	2 for the rdlen
	4 for the rdata

	65535/16 = 4095

	Mark


> Thanks in advance.
>  
> Tom Byrnes
> CTO
> ThreatSTOP
> 
> 
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org


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