The MPLS WG Archive

[Jean Philippe Vasseur <jvasseur@cisco.com>]

Hi Sanddep,

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

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.

> 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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