Mike Brescia (brescia@BBNCCV.ARPA)
17 Feb 86 10:51:21 EST (Mon)

     Does anyone know why the IPTO gateway on ARPANET is sending ICMP redirects
     to my MILNET hosts?


There were three separate factors which conspired together (&&) to cause the
newly installed IPTO butterfly gateway to send you (and others) redirects.

1. the redirect code did not include the test that the IP source of the packet
   must be on the same net as the gateway's input interface to permit a
   redirect to be sent.

2. the butterfly gateway includes minimal GGP code to advertize its own
   connected net (ARPA-LAN, 192.5.18, in this case) to those 'core' gateways
   which ask.

3. the butterfly gateway was plugged in to replace an lsi-11 'core' gateway,
   but the plug transfer was done too fast (5 seconds rather than 5 minutes)
   for the other core gateways to notice the fact that a core gateway had gone

Because of (3), the core gateways did not get any new information from
IPTO which would have only listed the ARPA-LAN net. This meant that when some
nets went down, a route was mistakenly thought to exist through IPTO.

Because of (1), IPTO was sending redirects for these packets not only to
arpanet hosts, but also to hosts on milnet and other nets farther out.

On Thursday morning, about 1100 EST, the IPTO gateway was brought up after
being down for at least 10 minutes, forcing the core gateways to clear out the
extraneous information. Friday, the gateway was reloaded with the redirect
bug fixed.

Mike Brescia

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