DNS Query Behavior with Global Forwarders Statement

[Merton Campbell Crockett]

My corporate network consists of roughly 100 different sites located  
throughout North America.  At each site there is a Network Management  
System (NMS) running ISC BIND and DHCP.  Each NMS is the master name  
server for the forward and reverse DNS zones assigned to the site.

No NMS has direct access to the Internet and forwards all DNS queries  
to a regional name server that has access to the Internet.  The  
forwarders are defined as follows.

	options {
		...
		forward only;
		forwarders { 10.73.2.6; 10.10.2.6; 10.35.2.6; };
		...
	};

The order in which the forwarders changes depending upon the region in  
which the site is located.

I was asked to look at a problem involving name resolution at several  
sites.  I had expected to see all DNS queries being forwarded to the  
"closest" regional name server.  What I found using tcpdump was that  
all name servers in the list were being used in a round-robin fashion,  
i.e. I would see a group of queries sent to the first name server, the  
second name server was used for the next group, the third was used for  
the next group before the cycle restarted.

Is this an artifact of the -P2 changes or was the use of RTT dropped  
for some other reason?


Merton Campbell Crockett
m.c.crockett at roadrunner.com