Re: FATAL: Too many queued dnsserver requests

From: Patrick McManus <>
Date: Mon, 28 Jun 1999 08:50:31 -0400 (EDT)

In a previous episode Clifton Royston said...
:: > If you have a slow saturated link then long service times for DNS
:: > queries is normal. (long service time for any type of requests on a slow
:: > saturated link is normal).
:: However, DNS tends to suffer in particular, because UDP doesn't get
:: the automatic low-level retransmits that TCP applications do - the
:: timeouts and retransmits will be happening at a speed dictated by the
:: DNS requester's own timeouts instead of at the (usually more optimized)
:: protocol level.
:: I would guess that you are seeing a significant fraction of all
:: incoming or outgoing IP traffic over that link being dropped out of
:: your router's buffer, and then corrected by TCP retransmits. The DNS
:: queries being dropped won't be automatically retransmitted at the same
:: rate, most likely; however, you may be able to work around this problem
:: by finding the retry interval for your DNS server and tuning it down
:: until it starts performing better.

it appears as though you're recommending injecting traffic faster into an
already congested network.. that's the recipie for congestion
collapse.. under those kinds of circumstances you want to run DNS
under TCP, which is congestion controlled. While in the general case
that isn't really feasible if you have one recursive resolver you use
on the other end of the saturated link, that forwarded can essentially
exapnd your requests into UDP for you there...

Received on Mon Jun 28 1999 - 06:50:03 MDT

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