Subject: [CCAMP] Looking for clear direction about RRO generation for bidirectional LSPs

From: "Schwager, Steven D." <[email-masked]>
Date: Fri, 12 Feb 2010 11:07:12 -0600

Any,

Even after reading RFC 4990's clarifications on RRO processing, my colleagues and I are still uncertain how to interpret certain statements in some of the RFCs.  I was hoping a simple example would eliminate our confusion.

In the following diagram, nodes A, B and C are connected by numbered interfaces 1, 2, 3 and 4.

 -----         -----         -----
|     |1     2|     |3     4|     |
|  A  |-------|  B  |-------|  C  |
|     | lbl=x |     | lbl=y |     |
 -----         -----         -----

A bidirectional LSP is established from A to C, using label x upstream and downstream from 1 to 2, and label y upstream and downstream from 3 to 4.  Label recording for the RRO is enabled.  The nodes are recording incoming and outgoing interfaces.

Our best guess is that RRO carried in the updated PATH message (updated to carry downstream label info) from B to C would be: RRO=(3,y,y,2,1,x,x), where 3 is the first subobject relative to the beginning of the RRO.  3, 2 and 1 represent subobjects for numbered interfaces.  y and x represent subobjects for labels.

Our best guess is that the RRO carried in the RESV from B to A would contain the following subobjects: RRO=(2,3,y,y,4).

Note 1: The above subobjects pushed by node B for the PATH appear to conflict with statements made in RFC 4990 (6.1.3 "4. Link ID identifying the incoming (upstream) TE link, followed by a Link ID identifying the outgoing (downstream) TE link, optionally followed by a Component Interface ID and/or one or two Labels.")

Note 2:  The above subobjects only include labels for the outgoing links (per RFC 4990).

Can anyone confirm or correct the RROs in the PATH and RESV examples?

Best Regards,
Steve Schwager