[SURBL-Discuss] Combined SURBL A record format (Was: Re: Bill Stearns' sa-blacklistavailable as SURBL: ws.surbl.org)

Jeff Chan jeffc at surbl.org
Wed Apr 21 02:42:08 CEST 2004

On Wednesday, April 21, 2004, 1:29:27 AM, Scott Truman wrote:
> I'm happy with either method obviously. Excuse my ignorance
> with regards to DNS lookups, but do all the A records come down
> with the first DNS lookup, or are they fetched each time from
> the remote 
> server?
> What are the traffic overheads with incorporating either type
> of method - I would have thought that the bit mask method would
> cause less traffic - also with smaller zone transfers? 

Hi Scott,
Multiple A records can result from a single query:

> % nslookup www.yahoo.com

> Name:    www.yahoo.akadns.net
> Addresses:,,,
> ,,,
> Aliases:  www.yahoo.com

And they should all come from the locally cached copy of the zone
file, so they're fast.

A single bitmasked A record would be smaller but require a little
more application CPU to decode.  Multiple A records may be faster
but they're bulkier.  I find the multiple A records more readable.
It's one of those classic tradeoffs.

Jeff C.

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