Subject: question on backup facility

From: "Sandeep B" <[email-masked]>
Date: Wed, 30 Oct 2002 23:44:50 +0000

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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From: Jean Philippe Vasseur <[email-masked]>
Date: Wed, 30 Oct 2002 21:16:43 -0400

Hi Sanddep,

At 23:44 30/10/2002 +0000, Sandeep B wrote:
>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)

This case is covered in the draft already:

When a downstream LSR detects a local link failure, for any protected
LSPs routed over the failed link, Path and Resv state MUST NOT be
cleared and PathTear and ResvErr messages MUST NOT be sent
immediately. Further a downstream LSR SHOULD reset the refresh
timers for these LSPs as if they had just been refreshed. This is to
allow time for the PLR to begin refreshing state via the bypass
tunnel. State MUST be removed if it has not been refreshed before
the refresh timer expires.

JP.