The MPLS WG Archive

[David Charlap <david.charlap@marconi.com>]

Santosh Gupta wrote:
>> 
>> interface addresses may be assigned to any interface of a router.
>> Also, an LSR that shares more than one link with a peer LSR will most
>> likely use its router ID as its LDP ID (address portion) in order to
>> avoid
> 
> I cant make out what do you mean by router ID. If a router has "n"
> cards then it will have "n" IP Addresses corresponding to each card.
> Where is this concept of router ID? Or is it the Internal
> representation (some no. assigned ) at an LSR for the peer that you
> are refering to ?

Not necessarily.  There is a concept of an "unnumbered link", where a
port does not have its own address.

With many routing protocols, unnumbered links may be used for routing,
as long as there's a way to uniquely identify each router.  this is the
"router ID".  The router ID may be administratively assigned or it may
be dynamically assigned (eg. by choosing one address from those in use
by local ports that have IP addresses).

>From the standpoint of a routing/forwarding table, a next-hop address of
a router ID address means "any port on that switch, I don't care
which.".

-- David