>>> Why is this (having a route pointing to a gateway that's not on net
>>> for any interface) not supported,
>> My guess is, because it does not match IP's routing model,
> Well, it seems to match the routing model of source routing, but I
> would like to know for sure, as I'm not very familiar with source
> routing.

Hmm.  Yes, if what it does is construct an LSRR (or perhaps even SSRR)
option on outgoing packets, and is ultimately grounded in a
directly-reachable host, I believe you're right.

My apologies.  I was (mis)reading your suggestion as being a slight
variant of the original one, which it's not.

>> But quite aside from what it does to the assumptions underlying IP,
> What does it do to the assumptions underlying IP concretely?

That every host that can send a datagram into a network has an address
in that network.  (This is why your suggestion, constructing a
source-route option, isn't actually a problem, because it doesn't
involve hosts sending into networks to which they have an interface
physically connected but in which they do not appear in IP terms.)

>> how would you cut off infinite loops?
> Isn't the Source Routing option (for IPv4) limited in size?  There
> would be no point in having more loops than this limit.

True, and that limit _is_ relatively small.  Okay, I'm answered.

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