Routing

Hi Experts

When we are using the node-link protection and if protected link or node fail then from the PLR (Point of local repair) router, outer label would be the bypass LSP label but how PLR knows the inner label which is between PLR'S next-hop router to next-nexthop router?

Thanks in advance

Hi,

RFC 4090 explains this operation. By using the session attribute "label recording requested" flag, the headend router requests that all downstream inbound labels are recorded in the RRO. So the PLR can examine this RRO and determine the correct label:

6.4.1.  Discovering Downstream Labels

   To support facility backup, the PLR must determine a label that will
   indicate to the MP that packets received with that label should be
   switched along the protected LSP.  This can be done without
   explicitly signaling the backup path if the MP uses a label space
   global to that LSR.

   As described in Section 6, the head-end LSR MUST set the "label
   recording requested" flag in the SESSION_ATTRIBUTE object for LSPs
   requesting local protection.  This will cause (as specified in
   [RSVP-TE]) all LSRs to record their INBOUND labels and to note via a
   flag whether the label is global to the LSR.  Thus, when a protected
   LSP is first signaled through a PLR, the PLR can examine the RRO in
   the Resv message and learn about the incoming labels that are used by
   all downstream nodes for this LSP

Thanks a lot ... Great Explaination .... I did not find this anywhere in Juniper documentation 🙂