The MPLS WG Archive

["Don Fedyk" <dwfedyk@nortelnetworks.com>]

Title: RE: CR LDP Local repair

Vijay

 

I checked with our developers and they said that if B asks for a label it should get a mapping response even though the LSPID is the same. You can determine it is a request from a new neighbor from the LSP Identifier which has a router ID of B at D. Therefore D should return a mapping to B for the new LSP segment. When B receives the mapping it can swap the LSP and terminate the LSP to C and D. Note the developers said that it is a local matter at D to terminate the label release beyond D if the LSP continues after that.

 

Hope that answers your questions,

Don

-----Original Message-----
From: Vijayanand C - CTD, Chennai. [mailto:vijayc@ctd.hcltech.com]
Sent: Tuesday, December 18, 2001 2:59 AM
To: Fedyk, Don [BL60:1A00:EXCH]
Cc: mpls@uu.net
Subject: FW: CR LDP Local repair

Don,

I understand that CR LDP basically  uses LDP signalling procedures. According to that when there is a next hop change the label with the old next hop is released, because CR LDP uses Dod Conservative retention mode.Then the request is sent to new NH.

 

The issue I am asking is how does the LSR at node D behave when it receives another request for existing LSP(same LSPID) from B. Remember the request is not a modification request.  Will LSR at node D give a new mapping to node B when LSP with same LSPID exists through BCD. 

 

Vijay

-----Original Message-----
From: Don Fedyk [mailto:dwfedyk@nortelnetworks.com]
Sent: Friday, December 14, 2001 8:12 PM
To: Vijayanand C - CTD, Chennai.
Subject: RE: CR LDP Local repair

Vijay

 

You said this was a loose path. Loose paths take the shortest hops. Mapping messages may arrive unsolicited or a new mapping is solicited based on that IP forwarding changing. This is all under control of the LSP. If the path is not pinned then it accepts the new mapping and releases the old.

 

Don

-----Original Message-----
From: Vijayanand C - CTD, Chennai. [mailto:vijayc@ctd.hcltech.com]
Sent: Friday, December 14, 2001 4:16 AM
To: Fedyk, Don [BL60:1A00:EXCH]; mpls@UU.NET
Subject: RE: CR LDP Local repair

Don,

If node D receives a new request with same LSPID from B will it return a mapping for that, given that an LSP with same ID exists in D with C as upstream. So , should 'nt the existing CR-LSP be released first.

 

Vijay

-----Original Message-----
From: Don Fedyk [mailto:dwfedyk@nortelnetworks.com]
Sent: Friday, December 14, 2001 1:45 PM
To: Vijayanand C - CTD, Chennai.; mpls@UU.NET
Subject: RE: CR LDP Local repair

Vijay

A couple logic flaws.

1) don't release B-C before new B-D mapping is received.
2) Loose hops shouldn't have bandwidth constraints, think about it, a loose hop has to follow the best route and can't do admission control.

Don

> -----Original Message-----
> From: Vijayanand C - CTD, Chennai. [mailto:vijayc@ctd.hcltech.com]
> Sent: Friday, December 14, 2001 12:48 AM
> To: mpls@UU.NET
> Subject: CR LDP Local repair
>
>
> Hello all,
> I have a question on the signalling funcionality in CR LDP
> for local repair.
>
> Consider the topology below.
>
>                      ---------- C ------------
>                      |                         |
>           --A ---  B ---------------------- D--
>
>
>
> Assume a tunnel exist across A-B-C-D( loose ER Hops as B D  )
>  Suppose a
> route update happens at node B with the next hop for node D
> being node D
> itself(may be due to BW constraints the CSPF has taken this
> decision and LSP
> is now going straight through). At this point node B sends a
> release along
> CD to release the old segment and a request to D.  In case,
> the request
> (which has to travel just one hop) arrives earlier than the
> release( which
> has to be processed at CR LDP at node  C ) at node D, then
> the request would
> be rejected by node D because the request is not a
> mdification request but a
> request for existing LSP itself !!
>
> This situation would occur more consistently if the original
> path that is
> released were more longer than the new path. 
>
> How does CR LDP handle such a signalling scenario?
>
> Thanks in advance,
> Regards,
> Vijay
>
>