While it would be nice if we didn't have to explain why simple explanations are inadaquite for complex systems, this is the real world. Simple explanations can cover 80-90 percent of the cases but there are always cases that cant be explained easily. If equipment is designed for optimal icmp handling, what are you willing to give up? Cisco does a prety good job of handling icmp in a timely fashon.
I have seen other equipment that exibits hard to explain behavior. In particular, an Extreme Networks core switch that delayed icmp echo traffic for over 1000ms for a several second period every 5 minutes. And this was transit traffic not replies from the switch itself. It took a long time to convince management and other engineers that production traffic was unafected and we didn't have a BIG problem. When I get someone who is complaining about ping times, I like to ask for a traceroute. They usualy will come back and show me that hop x is slow. And as often as not, I get to ask them how can it be that they can get to hops after x faster than they can get to x? Light bulbs go on at this point. Granted I am usualy talking to someone with an IT background and users at the end of a DSL or cable circuit are a different matter. From: Brian Dantzig Senior Network Engineer Medline Industries, Inc. -----Original Message----- From: cisco-nsp-boun...@puck.nether.net [mailto:cisco-nsp-boun...@puck.nether.net] On Behalf Of John Elliot Sent: Wednesday, August 24, 2011 5:58 AM To: benny+use...@amorsen.dk; sth...@nethelp.no Cc: cisco-nsp Subject: Re: [c-nsp] reliability of ping to router physical-, sub- or loopback interface > > Latency tests are often useful for debugging, and ping is an easy-to-use > and widely available tool for latency testing. Having to start an > incoming support call by explaining why a high varying latency as > measured by ping does not actually mean that something is wrong easily > wastes a couple of minutes. Even worse if that was the only "problem" > the customer had. > > So please, router vendors, make ICMP ECHO fast and reliable. > Ideal world yes, ping is a useful tool for latency testing, but it is unfortunately abused...hardly ideal to give icmp a priority for packets destined TO router...far more important roles for a router to do than prioritize an icmp flood to a local int. _______________________________________________ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/ _______________________________________________ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
