Subject: Aggregation based on DU/O

From: Jim Sullivan <[email-masked]>
Date: Mon, 30 Aug 1999 11:29:54 -0400

The architecture spec, in section 4.1.6
"Option: Egress-Targeted Label Assignment"
contains the following text. 

   There are situations in which an LSP Ingress, Ri, knows that packets
   of several different FECs must all follow the same LSP, terminating
   at, say, LSP Egress Re.  In this case, proper routing can be achieved
   by using a single label for all such FECs; it is not necessary to
   have a distinct label for each FEC.  If (and only if) the following
   conditions hold:

      1. the address of LSR Re is itself in the routing table as a "host
         route", and

      2. there is some way for Ri to determine that Re is the LSP egress
         for all packets in a particular set of FECs

   Then Ri may bind a single label to all FECS in the set.  This is
   known as "Egress-Targeted Label Assignment."

   How can LSR Ri determine that an LSR Re is the LSP Egress for all
   packets in a particular FEC?  There are a number of possible ways:

     - It is possible to use the label distribution protocol to pass
       information about which address prefixes are "attached" to which
       egress LSRs.  This method has the advantage of not depending on
       the presence of link state routing.

If using Downstream Unsolicited/Ordered control to accomplish 
aggregation, is it still a requirement to have a "host route" to 
the egress LSR at each LSR along the LSP ?
 
For example if the strategy in some network is to 
use the label distribution protocol to distribute aggregation 
information from egress to ingress, must the FEC associated 
with the host route to the egress(i.e. a 32 bit prefix FEC) be 
included in the label mapping messages which are propagated upstream ? 
And what would the rules be for processing such a label mapping 
message, which included this address prefix FEC in addition to 
all the other FECs for which the egress LSR was an egress for.

Jim