Re: DOWN WITH DUMB GATEWAYS!


MILLS@USC-ISID.ARPA
6 Feb 1986 18:35:33 EST


In response to the message sent 6 Feb 1986 8:39:25 EST (Thursday) from louden@mitre-gateway.arpa

Mike,

In BBN's defense, remember that the LSI-11 gateways were evolved way
beyond reasonable conjecture from the first design, include protocol
support (EGP and VAN) unanticipated in the original design and are deployed
in much greater numbers of gateways and networks than are reasonable
with this design. The Buttergates were evolved precisely in response to
many of the existing problems and, assuming money to pay for them is
found, should eventually overtake the LSI-11s.

The presence of apparent routing loops in updates received from the core
system is an expected consequence of the intrinsic GGP routing protocol used in
the LSI-11 gateways for the last seven years. This protocol, as well as other
similar protocols based on min-hop algorithms can for form transient loops when
various nets bob up and down and the hop-count fields are "counted to infinity."
The problem has been long recognized and has nothing intrinsically to do with
EGP or even the particular implementation, but is an intrinsic problem with
min-hop algorithms. The SPF algorithm developed for the ARPANET and adapted for
the Buttergates should make these loops much less likely.

You might speculate on what might happen if we did not have EGP and peered GGP
directly with the core instead. Before we had EGP there was this incident that
became enshrined in legend and called the Great Commando Raid. Someday either
Mike Brescia or I will include that chuckle in our memoirs. The circumstances
were funny enough and won't be repeated here; however, the result was a new
packet type, called the Kiss of Death (KOD) packet, that killed the recipient,
but not before forwarding the packet to the next victim.

Dave
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