North American Network Operators Group

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Re: backbone routers' priority settings

  • From: Vaananen Pasi NTC/Boston
  • Date: Tue Feb 03 17:43:44 1998

>>> 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.

>Where is ICMP made obsolete or recommended against?  I don't see it.

>From rfc1812: ... stuff deleted

Also from RFC1812: Source Quench

   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

      Research seems to suggest that Source Quench consumes network
      bandwidth but is an ineffective (and unfair) antidote to
      congestion.  See, for example, [INTERNET:9] and [INTERNET:10].
      Section [5.3.6] discusses the current thinking on how routers
      ought to deal with overload and network congestion.

   A router MAY ignore any ICMP Source Quench messages it receives.

      A router itself may receive a Source Quench as the result of
      originating a packet sent to another router or host.  Such
      datagrams might be, e.g., an EGP update sent to another router, or
      a telnet stream sent to a host.  A mechanism has been proposed
      ([INTERNET:11], [INTERNET:12]) to make the IP layer respond
      directly to Source Quench by controlling the rate at which packets
      are sent, however, this proposal is currently experimental and not
      currently recommended.