[c-nsp] IPv6 subnets for point-to-point links

[Andre Beck]

Hi,

On Tue, May 10, 2005 at 05:48:48PM +0300, Yucel Guven wrote:
> Crist,
> Routers need to identify networks uniquely,

Today routers don't think in "networks". They think in routes.

> e.g, if a router has 50 x p2p subinterfaces, it must know into which
> subif the packet has to be forwarded.

Of course. It does so by consulting its routing table.

> For this purpose, netmasks are inevitable.

By no means. There are several ways to run a router as described above
(one Ethernet to backbone, a hell of a lot of PTP interfaces to elsewhere)
with a single IP address. The two most common methods are

a) Special interface type "point to point" that trades the normal
   ip/mask value pair of a MA network interface against a local
   address/remote address pair. It implicates a connected host route
   to the remote address. The local address is just informational
   and can be shared with other interfaces.

b) Special interface type "unnumbered" that has only a local address
   borrowed from another interface (that's the Cisco way). Therefore
   it implicates no connected route at all. You define them manually
   by pointing a route directly to the interface.

Today, the routing table and the notion of "connected routes"
has completely removed the need for a router to deal with networks
and reachability relations directly wired to interfaces.

Of course there are reasons to run PTP links numbered. They are
mostly due to the ways routing protocols work and establish their
topology. But it's not an IP axiom to always have networks with
masks, you can live perfectly without them if paying certain
attention and not running certain dynamic routing protocols.

-- 
                  The _S_anta _C_laus _O_peration
  or "how to turn a complete illusion into a neverending money source"

-> Andre Beck    +++ ABP-RIPE +++    IBH Prof. Dr. Horn GmbH, Dresden <-