[6536] in North American Network Operators' Group
Re: NAP/ISP Saturation WAS: Re: Exchanges that matter...
daemon@ATHENA.MIT.EDU (David Miller)
Thu Dec 19 15:56:16 1996
Date: Thu, 19 Dec 1996 15:25:47 -0500 (EST)
From: David Miller <david@sparks.net>
To: Chris Caputo <ccaputo@alt.net>
cc: nanog@merit.edu
In-Reply-To: <Pine.BSI.3.93.961217002946.28018A-100000@baklava.alt.net>
On Tue, 17 Dec 1996, Chris Caputo wrote:
> There is considerable difference between forwarding a packet that happens
> to contain ICMP data (destination not the router) and responding to a
> packet that contains ICMP data (destination is the router). In the
> former, priority in a Cisco is the same for ICMP as it is for UDP or TCP,
> since this part of the packet is not even being examined. In the later,
> priority is lower and can be ignored altogether.
>
> I treat ignored (link good, but no response received) ICMP echo requests
> as an indicator that a router is too loaded. If the router has been
> pushed to the point of not being able to respond to an ICMP, how well is
> it going to do when a bunch BGP updates occur? (rhetorical) Both are CPU
> intensive operations.
Would someone please tell me just why icmp echos are "cpu intensive"?
Yes, I know they're in software. So what? A PC can respond to an
ethernet loaded with them with a trivial percentage of it's CPU cycles.
This sounds to me a whole lot more like a solution to an imagined
problem, but I'm prepared to be convinced that responding to pings
actually takes a great enough percentage of CPU cycles to slow down
packet delivery.....
Thanks,
David
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It's *amazing* what one can accomplish when
one doesn't know what one can't do!
