The MPLS WG Archive

["Sandeep B" <san_101@hotmail.com>]

As per my understanding for backup path to work with global label space is 
to keep all path states intact on a downstream node (MP) when an 
intermediate link fails (between PLR and MP)

With most of the implementations I see today all path states are removed
once a upstream link failure is detected on a router and PATHTEAR is
send downstream.

So my statement would be correct that "only way for backup facility to work 
is to replace all nodes in the network". With even one intermediate node 
behaving to not keep its PSB states on upstream node/link failure would 
bring down the Lsp and potentially creating a black-hole for a while (as PLR 
would think that backup facility is still in use even though MP has removed 
its path/resv state on getting a PATHTEAR from NHOP with respect to PLR)

Comments??

-Sandeep


4.5.1. Path state

   Path state for every locally repaired LSPs is refreshed downstream by
   the PLR. These Path messages use a new SENDER_TEMPLATE value (the
   IPv4 tunnel sender address is set to a PLR address), and are sent
   onto the bypass tunnel with changed PHOP, ERO and RRO.

   When a local link fails, there could be some protected LSPs using
   this link.
>>>At this point, the LSR MUST NOT remove the state (Path
   and Resv) and send PathTear and ResvErr messages that are
   corresponding to these LSPs immediately.





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