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SRLG support by CISCO

  • From: mohanss <mohanss@huawei.com>
  • Date: Tue, 12 Apr 2005 10:23:23 +0530
  • Importance: Normal
  • Organization: huawei technlogies
  • Resent-Date: Tue, 12 Apr 2005 00:55:25 -0400
  • X-Scanned-By: MIMEDefang 2.45

Title: SRLG support by CISCO

Hi all,

CISCO is supporting SRLG for MPLS RSVP tunnels. This information I got through from few of the CISCO documents.
I have few doubts regarding this.

Consider the following network:


                       v3      
                    /      \
                  /          \
              1 /              \ 2
              /                   \
             /       1          1    \       1
           s -------- v1 ----- v2 ------- t
                        \                      /
                          \                  /
                            \              /
                           1 \          /  2
                                \            /
                                 v4



In the above case there exists two SRLG disjoint paths from source "s" to destination "t".
First path      : s-->v3-->v2-->t
Second path     : s-->v1-->v4-->t

But if we consider the shortest path it is s-->v1-->v2-->v4.

So for Auto-tunnel backup with cisco how it will work? I mean if we enable CSPF, it will give the shortest path as s-v1-v2-t, then

It cannot find the SRLG disjoint path. But if it gets PATHS as listed above (s-v3-v2-t and s-v1-v4-t) then it will satisfy the SRLG disjoint condition.

How CISCO Routers handle this situation? Can anybody who has expertise on CISCO clarify this?

Thanks,
~Mohan