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Re: large organization nameservers sending icmp packets to dns servers.
But why would they care where the nameserver is? Point 2 would seem to be a little stupid a thing to assume. Also, what happens if, at that moment, the ICMP packet is stuck in a queue for a few ms making the shortest route longer. -- Leigh Valdis.Kletnieks@xxxxxx wrote: > On Mon, 06 Aug 2007 11:53:15 EDT, Drew Weaver said: > >> Is it a fairly normal practice for large companies such as Yahoo! And >> Mozilla to send icmp/ping packets to DNS servers? If so, why? >> > > Sounds like one of the global-scale load balancers - when you do a (presumably) > recursive DNS lookup of one of their hosts, they'll ping the nameserver from > several locations and see which one gets an answer the fastest. > > Yes, it's a semi-borkken strategy, because it assumes that: > > 1) ICMP is handled at the same rate as TCP/UDP packets in all the routers > involved (so there's no danger of declaring a path "slow" when it really isn't, > just becase a router slow-pathed ICMP). > > 2) That the actual requester of service is reasonably near net-wise to the > server handling the end-user's recursive DNS lookup. >