🚀 go-pugleaf

In article <Mar.26.16.30.50.1989.18182@NET.BIO.NET> lear@NET.BIO.NET (Eliot Lear) writes:
>An IP address does not imply a
>route.  Given an address and nothing more, one cannot determine a
>route.  Never-the-less, in order for an Internet to be well connected,
>routing information about an address must be kept, if nowhere else, at
>the entrance points to an internet (in the simplest case).  I see
>things from the DARPA Internet point of view.  How is routing done
>with ISO IP?
>

In IP, an address does imply a route.  For example,  the address of
a hypothetical CPU is 128.196.3.12.  This is a class B address, so
the Internet knows that it has to know where 128.196.x.x is, and
the routing is hierarchically dealt with from there.

If I move that CPU to some other campus, the address must change, because
the address implies a route (note that the NAME doesn't have to
change; just the address).  

More subtly, given a campus 128.196.x.x, where there are multiple
routes from that campus to the "world,"  the IP addressing/routing
schemes require that one manually insert any routing information
which isn't "fewest hops" in nature, and even then, the autonomous
system aspect of IP doesn't necessarily allow that minimal information
to flow from a campus to some other site.  As an example, again,
given that Arizona is connected to Purdue, Utah, and JVNC, it is
pretty obvious that Purdue knows not to go through either Utah or
JVNC to get to Arizona.  However, the next stop from Purdue, let's
say Indiana (hypothetically), has to manually be taught the Internet
topology, and can't learn the best way to get from here to there.
In any case, it's the addressing scheme which restricts the
routing scheme.

Some regional networks (like NSFNET) use a scheme where the entire
topology of the network is learned by routers.  This is OK as long
as you have enough memory to keep your entire topology in core, AND
as long as you're willing to not allow any granularity of routing 
beyond that which IP addresses give you. 

In both instances, the simplifying assumption which makes the
Internet work (and it's a miracle that it does) is that IP addresses
imply hierarchical routing. 

(I reference Paul Tsuchiya's work "Landmark Routing" for an excellent
solution to this and my own expansion on Paul's work, "Traveler Routing")

Finally, to answer your question, ISO IP doesn't imply routing; the
OSI model divides the network layer into a variety of sublayers, and
routing and IP are completely separate.  The framework for OSI-style
routing has been created, but the actual protocols and algorithms
are still a matter for discussion.

Joel Snyder
U Arizona MIS Dep't