NAP/ISP Saturation WAS: Re: Exchanges that matter...

Chris Caputo ccaputo at
Tue Dec 17 08:52:11 UTC 1996

> What you say here makes sense to me.  But, out of a 500 
> ping sample over the course of half a day, I was getting well
> below one percent loss -- six months ago.
> Now, my same sample group is going for more than three percent,
> with many ten percent loss routes showing.  This has changed and
> has changed commensurately with the throughput problems shown
> in TCP and name lookup problems via UDP.
> It may not be scientific proof, but it could very well be a good
> scientific indicator.  An indicator is all I really need for the
> most part.

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. 


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