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  > I am sure there must be some config command to bypass this problem.
  > Or is everyone wasting oodles of address space on their leased line
  > subnets?


You can use the ip-unnumbered feature to conserve addresses, if your routers
are all ciscos and if ip-unnumbered suits your needs.  If you can afford to
wait, you can eventually use OSPF or RIP II, though I have no comment on either
their availability or stability.

We use the following scheme to "conserve" subnets on a lot of our
point-to-point serial links today.

What we've done is to set aside a couple of subnets dedicated to serial links.
These subnets will ultimately become "invisible" to the rest of the network.
The number of subnets you need to allocate depends on the maximum number of
serial links per router.  This is because you don't want to (or can't)
duplicate subnet numbers per router.

We use a standard subnetted class B network mask, 255.255.255.0 across our
entire network.  What we do on the serial links is duplicate the same subnet on
each serial link, with the host portion of the IP address unique for various
reasons.
For example, 
                   Router A       56k         Router B
                 128.221.183.5-----------128.221.183.105

                   Router C       56k         Router D
                128.221.183.15-----------128.221.183.115

Note that only one subnet was used for 2 completely separate serial links.
This subnet is utilized again and again...

The key to getting this to work is to prevent these "invisible" (actually
duplicate) subnets from getting into the outgoing routing updates.  Use the
"distribute-list out" command and access-lists (or equivalent) to keep these
subnets out of the RIP or IGRP routing updates.  The mindset here is that these
serial links are only there to gateway you to another subnet, i.e., your
ultimate destination.  Therefore the subnet's existence only needs to be known
and is only used by the adjacent router.

This works out quite well.  From a global network view, you get the same effect
as an ip-unnumbered interface, i.e., can't "see" (ping, etc.) the interface
from just anywhere anymore.  But you can still actually ping the serial
interface, if necessary, from the router directly connected to the other end of
the serial link.

There are some side issues related to SNMP traps, etc., which is one of the
reasons for unique host ids.  (nothing which hasn't been worked around :-)

Tom

Tom Karolyshyn
Data General Corp
Westboro, MA 01580
508-870-7936