[14928] in North American Network Operators' Group
Re: backbone routers' priority settings
daemon@ATHENA.MIT.EDU (Vaananen Pasi NTC/Boston)
Tue Feb 3 17:39:55 1998
From: vaananen@NASBPD01BS.ntc.nokia.com (Vaananen Pasi NTC/Boston)
To: dean@av8.com (Dean Anderson), marcs@znep.com (Marc Slemko)
Cc: nanog@merit.edu (nanog)
Date: Tue, 03 Feb 1998 17:00:09 -0500
>>> 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:
4.3.3.3 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
generated.
DISCUSSION
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.
DISCUSSION
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.
Pasi
