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From: Rudy.Nedved@H.CS.CMU.EDU.UUCP
Newsgroups: comp.protocols.tcp-ip
Subject: Re: ICMP in ISO
Message-ID: <1987.4.15.15.15.10.Rudy.Nedved@h.cs.cmu.edu>
Date: Wed, 15-Apr-87 10:44:36 EST
Article-I.D.: h.1987.4.15.15.15.10.Rudy.Nedved
Posted: Wed Apr 15 10:44:36 1987
Date-Received: Fri, 17-Apr-87 02:12:03 EST
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As someone said recently for why you want ICMP ECHO required is for debugging.
The application is to determine connectivity which you can not associate with
gateway mechanisms since routing updates are broken half the time. You really
need a simple way of to see if some node in the network tree is there.  You
test node A, you test node B and then test node C and then try X. This is
usually neccessary if you are trying to answer the question, "Why can't I talk
to X?".

The other things that PINGing is good for is testing for drop tests, different
packet sizes and random data failures. There are a variety of failure modes
related to interfaces, translating a packet from one network to another,
congestion versus media, packet sizes and a host of other conditions.

Basic horror stories include the following:
	SDLC interface that paused a bit longer between bits after 256bytes,
	the interface was correct but the old piece of garbage hardware on 
	the receiving side was slightly off...It would randomly pick a bit
	value for that bit. Pings using different packet sizes and data
	showed this.

	Oscillation failures between gateways. The gateways would believe a
	network was done when it is was up and vice versa. Pings helped
	detect this incorrect knowledge in the gateways.

	ARP mechanism is busted. A PING on one host said a host was up but
	on the busted host said it was down. 

	Connections dropping during end of day. PINGs showed that occasionally
	for a minute or so, all packets were lost. Turned out interface under
	high load would occasionally shut itself off....probably related to
	input buffer ring size.

In many cases, the thing that saved us was the fact that ICMP ECHO was
required. We could point at an implementation and say you are not playing
by the game rules and would treat them very badly...It never happened but
the ability is there.

I believe in the Ethernet configuration testing protocol. I look at ICMP
ECHO with source routing as being a mid-level network testing mechanism.
Losing this ability would hamper our ability to quickly track down problems.

If ISO has a better mechanism then simple ECHOs and ECHOs with source
routes, I would love to hear about it on this list since I am certainly
eager to learn better and faster ways to isolate network failures.

-Rudy