Subject: RE: RFC 1812 (IP Unnumbered)

From: vishwas <[email-masked]>
Date: Mon, 14 Dec 98 12:25:00 PST

> What problem. On Linux you set your address to be your lan side address
> or any other public address your host has, and you add a route of
>
> route add default dev ppp0

In other words, you route whatever is on the other side of the link by
specifying to route it to the device for the interface, rather than
specifying to route it to the IP address of the interface.

How you determine what is on the other side is another story (and perhaps
that is vishwas's real question), but hopefully you have some idea.

This would work, I suspect, much better with static routes than with
something like RIP.  In fact, I think most RIP daemons are constrained to
knowledge of IP addresses only.

[vishu]

True,
OK now how shall applications over IP like DVMRP and PIM behave over   
these IP unnumbered interfaces...?

---

From: Art Berggreen <[email-masked]>
Date: Mon, 14 Dec 1998 08:24:15 -0800 (PST)

>knowledge of IP addresses only.

Actually RIP works just fine with unnumbered interfaces.  In essence, a
RIP update states "you can reach the following set of IP prefixes by
sending through me".  If you receive the update on a numbered interface,
you need to remember both the interface and the next-hop IP address. If
you receive it on an unnumbered interface, all you need to remember is
the interface.  In RIP-V1 it was common to use the subnet mask of numbered
interfaces to derive the subnet mask of other subnets of the same base
network.  With RIP-V2 the subnet mask is carried and proper support for
CIDR is available.

Art