The MPLS WG Archive

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

Shahram,

Let us assume that detours from B and C don't merge at H. But these two LSPs share the same link between H-I. The at I there will be 2 detour LSP (B to D and another from C to E). 

If the detour LSPs use SE filter, then the RESV message from I to H can specify only one filter (Session + sender of all the detours will be the same) and only one Label. Which label does I select?

-sundara

-----Original Message-----
From: Shahram Davari [mailto:Shahram_Davari@pmc-sierra.com]
Sent: Monday, August 12, 2002 11:45 AM
To: Sundara Murugan; mpls@UU.net
Subject: RE: fast-reroute merging


Sundara,

I think the shortest ERO is only a suggested example. and not a standard rule.



                G----H----I--\
                |    |    |   \
           A----B----C----D----E---F


I think no merging should happen in the G, H and I LSRs. The reason is that
may be B has calculated the route B-G-H-I-D-E-F assuming some BW restrictions, etc.
We don't want H to change that to B-G-H-I-E-F.

Also since each PLR does an independent ERO calculation, it is quite possible 
for C to compute computes the path as being C-H-I-D-J-K-M-N-... Clearly C's detour should
not be merged with B's detour here.

If we have rule changed to "for merging the path messages should have the same ERO",
then we won't have such a problem.


-Shahram

> -----Original Message-----
> From: Sundara Murugan [mailto:smurugan@riverstonenet.com]
> Sent: Monday, August 12, 2002 2:22 PM
> To: Shahram Davari; mpls@UU.net
> Subject: RE: fast-reroute merging
> 
> 
> 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
> > 
> > 
> > 
>