[SURBL-Discuss] Hmmm....what if?

[Patrik Nilsson]

At 17:47 2004-08-03 +0100, Karanbir Singh wrote:
>Chris Santerre wrote:
>>What if I placed an SURBL server in the beginning of my DNS query list? Then
>>users would actually check SURBL for a domain in a web page. If it is in
>>SURBL they will get a 127.0.0.x and get error. Which is good!
>
>Works! All you need to do is add the multi.surbl.org ( or whatever list 
>you want to use ) to the Host Search order. So that x.com is looked up as 
>x.org.multi.surbl.org

This would only work for x.com, not www.x.com, etc.
The SURBL servers - correctly - return NXDOMAIN when queried for subdomains 
of listed domains, rather than treat the listed domains as wildcards.

Also - this generates a lot of unnecessary dns queries for non-listed domains.

First, your client queries a surbl NS server for the RR 
host.not-surbl-listed.com.multi.surbl.org.
Which results in a NXDOMAIN reply.

Your client then likely (exactly what happens depends on the specific 
environment) queries the surbl NS server for the RR host.not-surbl-listed.com.
Which results in a "not authorative" or "query refused" reply.

Only then does your client proceed to the next resolver in its list and 
queries it for the RR host.domain.com and eventually get a positive reply.

Patrik