large organization nameservers sending icmp packets to dns servers.

Patrick W. Gilmore patrick at
Mon Aug 6 18:27:15 UTC 2007

On Aug 6, 2007, at 1:47 PM, John L wrote:

>>> Why would they ping rather than just sending the query to all of the
>>> NS and see which one answers first?  It's an IP round trip either  
>>> way.
>> If you have sites in San Fran, London, and Tokyo, and you launch a  
>> ping from
>> all 3 and see which one gets there first, you'll *know* the RTT  
>> from each site.
>> If you just send DNS replies from all 3, you don't have a good way  
>> of telling
>> which one got to the destination first.
> Um, unless I seriously misunderstand the client DNS cache wants to  
> know which server is closest.  So it sends DNS queries to all three  
> NS at the same time.  Then it waits for the answers.  Whichever one  
> answers first is the closest.  What am I missing?

The client DNS doesn't know there is more than one server.  It  
queries for www.$, and the authority for $ replies with  
the IP address of the 'closest' web server.

This result could be pre-calculated by all the web servers pinging  
the client DNS.  It could be done lots of ways, but that is what we  
are discussing today.

Owen said it worked well for his customers (in a past life), and he  
has operational experience with this.  Can anyone give a serious  
counter example _from experience_?  Or are we just discussing  


More information about the NANOG mailing list