Re: More than one IP (sub)network on one ethernet cable

James B. VanBokkelen (JBVB@AI.AI.MIT.EDU)
Thu, 17 Dec 87 23:43:33 EST

If a gateway is present, it should be configured as such. If there is no
gateway, I can either return an error to the user, or ARP the address
on the other network anyway. If it is on another subnet which has suddenly
become irrelevant, re-configure and unset the subnet bits.

If I ARP it, maybe it is a spurious broadcast, maybe it works. If it
works, various clever bits of code that treat things routed via a gateway
differently break down, but the connection probably survives. To me, the
tradeoffs have seemed to favor returning the error. If the user is in the
what I think to be the mainstream, he has a configuration problem, and
should know about it.

Our code was recently reported (by a customer) to be willing to ARP any
address configured as a gateway, although it won't ARP off-net addresses
if no gateway is configured. I didn't design it, but it seems reasonable.


James B. VanBokkelen
FTP Software

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