[afnog] IIS & DNS

Mark Tinka mtinka at africaonline.co.zw
Wed Mar 8 08:37:44 EAT 2006


On Tuesday 07 March 2006 19:11, Brian Candler wrote:

> IIS probably calls the Windows resolver library, and
> the resolver library will make a DNS query.

It actually looks like Microsoft SMTP (which IIS uses to 
send e-mail) will only make DNS queries on TCP port 53, 
even though the size of the query response is < 512 
bytes.

> It can use 
> either UDP or TCP port 53. Normally resolvers don't
> choose TCP unless the response to a query is very
> large. However they are quite entitled to use TCP if
> they wish, which means it's not a good idea for your
> firewall to block this usage of DNS.

Okay.

Cheers,

Mark.
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