[SURBL-Discuss] Death By DNS

Rob McEwen webmaster at turnaprofit.com
Tue Jul 27 14:34:58 CEST 2004


RE: Death By DNS

I never mentioned this before, but these extra 
lookups can be like firecrackers going off. I 
do three types of DNS lookups:

(1) basic RBL checking of sending 
server's IP address using sbl-xbl.spamhaus.org

(2) content RBL lookup for domains and 
IP addresses using multi.surbl.org

(3) content RBL lookup for IP addresses 
(not domains) using sbl-xbl.spamhaus.org

(BTW - Does anyone have a "feel" for 
sbl-xbl.spamhaus.org and false positives. 
I wonder sometimes if that particular RBL
list is too strict?)

Anyway, the second and third of these two 
levels can sometimes cause several DNS
lookups per one singe message.

Eventually, I noticed that my server was
slowing down. Web sites were being 
served slower.

Also, my mail server software is 
NOT know for robustness
and several articles on their user's
group site mention that it falters
if the DNS server is slow or
has any problems.

So I thought... could there be a
connection?

My next "project" was to then
improve the DNS caching on my
Windows 2000 server. I tried to 
tweak the client DNS caching, but
with little success/options. Next, I
looked into installing the full Windows
2000 DNS service... but I'm not a
network engineer and the settings
seemed strange and the instructions
confusing.

Finally, I found the answer. I found
a 3rd party "caching" DNS server 
which works great for my purposes.

It has a lot of good features, like 
saving cached DNS data between reboots.

You can find this software here:

http://ntcanuck.com/

After installing it, I notice that web 
sites on my server which were
taking about 2 extra seconds longer
to load than they used to take started
flashing across the screen 
instantaneously.

I know that my conclusions about 
this are not scientific, but its hard
to argue with results.

Rob McEwen


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