North American Network Operators Group

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Re: backbone routers' priority settings for ICMP & UDP

  • From: Marc Slemko
  • Date: Tue Feb 03 16:59:19 1998

On Tue, 3 Feb 1998, Marc Slemko wrote:

> On Tue, 3 Feb 1998, Dean Anderson wrote:
> > 
> > ICMP in general is or should be given higher priority, since it is
> > necessary for congestion control.  Echo requests (pings) could be thrown
> Please, tell me of this magic ICMP that is used for congestion control. 
> Obsolete things that are now recommended against don't count. 

Since so many people are telling me all about the wonders of ICMP source
quench messages, may I remind them of section of RFC-1812 which

   A router SHOULD NOT originate ICMP Source Quench messages.  As
   specified in Section [4.3.2], a router that does originate Source
   Quench messages MUST be able to limit the rate at which they are

Sure, hosts can generate them, but that is seldom of much utility
(especially in the discussion here about network congestion control as
opposed to host/processing congestion control)  because the network is
more often the backlog than the host, and the host can't generate messages
saying the network is congested. 

ICMP messages are not a commonly used or particularily useful method of
congestion control on the Internet today.