RRSet size limitation lower than predicted by RDLENGTH field size

[Tom Byrnes]

Thanks for the response. I figured out where I went wrong.
FYI, it's less than 4095, because of the message header, and the first RR,
which includes the name :-)


So it's

INT((65535-(32+LEN(<name>))/16) + 1

Which works out to 4092 for a ThreatSTOP lookup.


-----Original Message-----
From: Mark_Andrews at isc.org [mailto:Mark_Andrews at isc.org] 
Sent: Thursday, April 24, 2008 11:37 PM
To: Tom Byrnes
Cc: bind-users at isc.org
Subject: Re: RRSet size limitation lower than predicted by RDLENGTH field
size 


> 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

No virus found in this incoming message.
Checked by AVG. 
Version: 7.5.524 / Virus Database: 269.23.4/1397 - Release Date: 4/25/2008
7:42 AM