The MPLS WG Archive

["Sundara Murugan" <smurugan@riverstonenet.com>]

Shahram,

Section 5.3.1 says that the MP selects the shorter ERO path length. This may not be correct.

If there are other routers between I and E, then the ERO lenght of the detour from C could be more than the ERO lenght of the detour from B. If you go by the rule, then H will merge the detours from B & C and establish a detour to D. Then the detour from C will not avoid its next-hop D. So there won't be a detour from C.

So the MP has to select the detour which merges with the main LSP that is closer to the egress router.

-sundara 


-----Original Message-----
From: Shahram Davari [mailto:Shahram_Davari@pmc-sierra.com]
Sent: Monday, August 12, 2002 10:57 AM
To: Sundara Murugan; mpls@UU.net
Subject: RE: fast-reroute merging


Sundara,

This is exactly the same question that I asked in another email:

"Since as stated in section 7, each PLR has option to apply its own constraints, then each PLR  may reach to a different backup-path ERO for the same flow. Assuming that the EROs have a single link (the downstream link of an MP LSP) in common, isn't it wrong for an MP LSR to merge those Path messages?"


I think the solution is to require the same ERO for merging.

Yours,
-Shahram




> -----Original Message-----
> From: Sundara Murugan [mailto:smurugan@riverstonenet.com]
> Sent: Monday, August 12, 2002 1:36 PM
> To: mpls@UU.net
> Subject: fast-reroute merging
> 
> 
> Section 5.3.1 in draft-ietf-mpls-rsvp-lsp-fastreroute-00.txt  
> explains merging procedure. In the fig below if there is a 
> link between I and F then D will have a detour D-I-F. In this 
> case how router I (the MP) handles detour LSPs from B, C and D?
> 
> -sundara
> 
> ------
> 
> 5.3.1. An Example on Path Message Merging
> 
> Consider the following example:
> 
> 
>                 G----H----I--\
>                 |    |    |   \
>            A----B----C----D----E---F
> 
> 
>    The protected LSP is A-B-C-D-E-F. After running CSPF, let 
> the detour
>    ERO from B be B-G-H-I-D-E-F, and the detour ERO from C be 
> C-H-I-E-F.
> 
>    H will receive Path messages that have the same SESSION and
> 
> 
>