RRSet size limitation lower than predicted by RDLENGTH field size
Tom Byrnes
tomb at threatstop.com
Fri Apr 25 20:39:34 UTC 2008
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
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7:42 AM
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