Re: RSVP-TE: specifying links in EROs

It would appear that I didn't phrase my original question clearly 
enough, given the nature of several responses I've received so far. 
Hopefully this will be better:

Suppose there are two routers with three links between them

       _________            _________
      |        A|----------|B        |
      |   R1   C|----------|D   R2   |
   ---|G       E|----------|F       H|----
      |_________|          |_________|

All of the interfaces have IDs (A-H).  These IDs may be IP addresses 
(numbered links) or they may be IF-IDs (unnumbered links).  Either way, 
they can all be uniquely identified.

If this would be an ATM network, it would be possible to signal a 
virtual circuit with or without specifying a particular link.  The DTL 
object (ATM equivalent of an ERO) can specify just node IDs, or it can 
specify port IDs as well.  If port IDs are specified, then the VC will 
be established over the link corresponding to that port.

What I can't find is some way of providing similar functionality in the 
MPLS world.

Clearly, if R1 and R2 are routable addresses acting as router IDs, and I
specify them in an ERO (R1, R2, ...), RSVP (running in R1) is free to
select any of the three links using whatever local criterial it
considers appropriate.

Suppose, however, that the ERO instead consists of ingress interface
addresses (G, B, ...) or of egress interface addresses (A, H, ...) or
perhaps even both (G, A, B, H, ...).  In these cases, has the ERO
specified that the LSP should be created over the A-B link?  Or are
these examples no different from the case of using router addresses?

My reading of the RFCs indicates the latter.  That no matter what
addresses you use in the ERO, you are only specifying nodes, and that
there is no way to specify the links.

There is nothing to prohibit RSVP from using interface addresses/IDs 
specified in ERO subobjects as an interface/link-selection mechanism.  I 
would even consider this a good practice.  But I also don't see anything 
in an RFC that could guarantee this behavior.

If there is an RFC-standard mechanism for specifying individual links, 
could someone post a reference to it?

If this is nothing more than a common practice, it would be nice to know 
it based on more than just my (almost certainly incomplete) reading of 
the RFCs.

-- David