how to handle Vitalink networks

11 Jun 86 12:34:18 EDT

We have an equivalent of your Vitalink network, using Applitek bridges.
We make sure that one gateways off that network does "promiscuous ARP".
This is a generalization of the "ARP hack" that has long been used for
subnetting. It generalizes it by having the gateways accept an ARP for
absolutely any address at all. If they are the appropriate gateway,
they respond with their Ethernet address. If not, they respond with
the Ethernet address of the correct gateway. (If you have several
gateways that do this, you can modify the code so that a gateway
does not respond for another gateway if the second is known to be
capable of responding for itself.) This is the ARP equivalent of an
ICMP redirect. Note that you only need one such gateway on a network,
since it can hand out the Ethernet addresses of the other gateways. This
is the only technique we can think of that can handle complex networks
built with systems like the Vitalink and Applitek. (I do not approve of
such bridges, but I can't prevent people from buying them, so I've had
to come up with a way to live with them.)

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