Re: Solicitation for comments

Charles Hedrick (
Tue, 17 Nov 87 20:52:16 EST

In the NSFnet at least, we are moving towards segmented or
hierarchical routing. It is unlikely that any gateway will know the
whole route for a trans-continental packet. We do not know any
routing technology that is currently up to handling the entire
Internet as a single-level metric. Thus we expect each campus, each
regional, and backbones such as Arpanet and NSFnet backbone, to be
"autonomous systems". They will exchange mostly reachability
information. Your own system will know a reasoanble exit gateway for
each destination, but may not know the exact route that will be used
to get to the final gateway. Thus a complete source route is not
going to work. It may be that loose source routing might be useful,
to specify which AS's are to be traversed. However I don't know of
anyone involved in setting up IP routing that is anxious to get
involved in this approach. If the gateways that go between the AS's
can get their act together, there should be no need to do source
routing. I see the primary disadvantage as being that the amount of
data needed to do a source route is going to be larger than that
required to do just the next hop. I think source routing may in fact
be useful for specifying major routing policy decisions. That is, if
a campus has a couple of major networks, one that is congested but
free and another that is pay, the user may be asked to specify that
he wants to pay by using a source route. That would probably be a
loose source route with just one entry, the gateway between the campus
and the pay network.

This archive was generated by hypermail 2.0b3 on Thu Mar 09 2000 - 14:39:56 GMT