The MPLS WG Archive

["Michael H. O'Meara" <mmeara@mars.iol.unh.edu>]

Hello all,
     While there's a thread on the subject, I was hoping that someone
might help clarify some of my confusion in regards to the processing of an
ERO. In particular, I'm having some difficulty understanding the selection
of a next hop for a node in the interior of an abstract node. According to
draft-ietf-mpls-rsvp-lsp-tunnel-07.txt, section 4.3.4.1:

5) Interior of the Abstract Node Case: Otherwise, the node selects a
   next hop within the abstract node of the first subobject (which the
   node belongs to) that is along the path to the abstract node of the
   second subobject (which is the next abstract node).  
...
6) Finally, the node replaces the first subobject with any subobject
   that denotes an abstract node containing the next hop.  This is
   necessary so that when the explicit route is received by the next
   hop, it will be accepted.

    What, exactly, is meant by "any subobject that denotes an abstract
node containing the next hop?" For example, given the following topology:

    A--B1--B2--B3--C

    Say that A sends an ERO={B,C}, where B describes an abstract node that
contains B1, B2, and B3, and B and C are strict hops. According to the
steps for making the selection of a next hop, B1 could send an ERO={B2,C}
to B2. Since C is listed as a strict hop, B2 would return a "Bad strict
node error." I may be missing something, but it would seem that nothing in
the steps for the selection of a next hop, nor in section 4.3.4.2 on the
addition of subobjects to the ERO, would preclude this from happening. I
would certainly appreciate any help in clarifying this matter.
			Thanks in advance,
				Mike    

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Michael O'Meara
Technician
MPLS Consortium	
InterOperability Lab
University of New Hampshire
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