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From: gds@SRI-SPAM.ARPA.UUCP
Newsgroups: mod.protocols.tcp-ip
Subject: Re: Redirect wars and Buterfly gateways
Message-ID: <8605192112.AA24302@sri-spam.arpa>
Date: Mon, 19-May-86 17:12:00 EDT
Article-I.D.: sri-spam.8605192112.AA24302
Posted: Mon May 19 17:12:00 1986
Date-Received: Tue, 20-May-86 20:19:55 EDT
References: <8605161029.AA11375@ucbvax.Berkeley.EDU>
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Approved: tcp-ip@sri-nic.arpa

> From: tom@LOGICON.ARPA (Jeff Makey , Tom Perrine)

> Speaking of brain-dead gateways, we have had some more instances of the
> ICMP "redirect wars".  This morning SRI-MILNET-GW redirected us to
> BBN-MILNET-GW, who redirected us back to SRI-MILNET-GW. This happened
> 11 times in 29 seconds while trying to establish a connection.
> A reponse came in 23 seconds, but after we had timed out.

This happens to me also.  Here's a sample netstat -r from sri-spam.arpa
(10.2.0.107/192.5.38.3).  It seems that our default gateway does not
always know how to get cross-net ...

Routing tables
Destination     Gateway         Flags    Refcnt        Use SWS pm Interface
default         10.1.0.107      UG            0         25  75  0 imp0
su-net-temp     sri-milnet-gw.a UG            0       1030  75  0 imp0
su-net-temp     isi-gateway.arp UG            0       1027  75  0 imp0
su-net-temp     stanford-gatewa UG            0       6071  75  0 imp0
su-net-temp     hazeltine-gw.ar UG            0          3  75  0 imp0
su-net-temp     sac-milnet-gw.a UG            0          3  75  0 imp0
su-net-temp     sri-gw.arpa     UG            0          4  75  0 imp0
su-net-temp     lbl-milnet-gw.a UG            0          2  75  0 imp0
su-net-temp     bbn-milnet-gw.a UG            0          4  75  0 imp0
su-net-temp     bbnnet2-arpanet UG            0          4  75  0 imp0
su-net-temp     bbn-van-gw.arpa UG            0          2  75  0 imp0
su-net-temp     crc-gw.arpa     UG            0          1  75  0 imp0
su-net-temp     bbn-cronus-gw.a UG            0          2  75  0 imp0
su-net-temp     isi-milnet-gw.a UG            0          1  75  0 imp0
su-net-temp     sri-csl-gw.arpa UG            0          2  75  0 imp0
su-net-temp     bbn-net-gateway UG            0          2  75  0 imp0
su-net-temp     dcec-milnet-gw. UG            0          1  75  0 imp0

Note the highest use count for the su-net-temp net is for
stanford-gateway, which is as it should be.  Some of the other gateways
mentioned are a little skeptical -- why would multiple gateways at BBN
be involved in what should be a decision strictly made in California?

One question is how your host handles redirects.  In 4.2, if there are
multiple gateways to the same destination, it attempts to share the load
between the two, by taking the lowest use count.  I have discovered
situations in which this may not be ideal.  4.3 attempts to be more
flexible by taking the route from the last redirect, and notifying any
connections of the route change (this is done in 4.2 BBN also).  There
is a short time in between the issuance of the redirect and the route
change for the connection in which the old route might be used, which
could cause a flurry of redirects.  I'd like to know how yours (and
others) IP routing implementations handle these sort of situations.
(I'd especially like to hear from the "hosts should be dumb, gateways
should be smart" folks.)

Back to the original topic, though, I have noticed similar behavior
going between sri-milnet-gw.arpa and bbn-milnet-gw.arpa for a lot of
connections I make (aside from the above, this happens for the rutgers
and mit-temp networks).

--gregbo