JAMA00

SCOM 2007 R2

another DNS tuning post!

Posted by rob1974 on July 6, 2010

 

Actually, this is my first DNS tuning post, but as the DNS mp has proven itself quite noisy you can find loads of other blogs with tuning tips. I haven’t found this one anywhere, so here goes my tip about the “DNS 200X Forwarder Availability Monitor” and why you should disable it or configure it properly.

What does this monitor do:

It just runs an A-record (ns)lookup for http://www.microsoft.com. So basically it assumes we have a forwarder in place and with http://www.microsoft.com we actually use this forwarder. Allthough many probably do (unless you use roothints), it’s actually a lot similar to the “DNS 200X External Resolution Monitor”, which does a NS-record lookup against http://www.microsoft.com (but override this to microsoft.com for a better result as that’s a correct ns-record lookup).

So the “forwarder availability monitor” doesn’t actually test forwarder availability, at least not which is already being tested by the external resolution monitor.

But there’s an use for this test. When you do use “conditional forwarding” in a DNS server, you can configure this test to lookup a domain record in the forwarding rule.

E.g. you have a conditional forwarding rule to “my2nddomain.com”. Set an override on the
“host” to a-valid-a-record.my2nddomain.com and actually make use of the forwarder availability monitor.

When you make use of conditional forwarders, configure this rule to actually use one of them. But when you don’t use forwarders or you use the “forward all domains” option, then just do like me and disable the monitor.

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