The MPLS WG Archive

["David Allan" <dallan@nortelnetworks.com>]

Sachin/Venkata:

 

You're mixing protection switching, and re-route scenarios. There are specific behaviors/state requirements depending on the recovery strategy,

    - LSR 16 may tell the ingress (revertive/non-revertive global repair),

    - LSR 16 may tell no-one (local repair), 

    - LSR 16 may tell EVERYONE (simple re-route) when the link goes down/comes back up.

 

later

Dave

 

 

From: Sachin Kalra [mailto:skalra@opnet.com]
Sent: Tuesday, October 09, 2001 1:17 PM
To: Naidu, Venkata; 'manis@futsoft.com'; mpls@uu.net
Subject: RE: LSP Failure/Recovery

Venkata:

Thanks for the email.

> Router 16 MAY indicate the ingress LER when the link between
>Router 16 and 17 comes back up. There are no hard and fast rules...

I agree with Mani in this case and suspect that "LSR 16 MAY indicate the ingress LER when the link between Router 16 and 17 comes back up."

Because
1> Why would LSR16 maintain information about the broken LSP (Which is not going through LSR16 any more, as may be the case that LSR14/15 or Ingress LER may have rerouted the LSP bypassing LSR16)

2> And if LSR16 does not maintain any state for broken LSP then it should not even know that it has to inform any LER (or other LSR) about the link recovery.

Please correct me if I am wrong.
Sachin

At 01:00 PM 10/9/01 -0400, Naidu, Venkata wrote:

Mani:

-> If you have a "local repair" support implemented, Router 16 will
-> reroute the LSP from itself (Router16) to the destination. It is not
-> required for the rerouting to be done from the Ingress or the head
-> of the LSP - which is known as "Global repair".

  Strictly speaking, there is no requirement that only the
  affected router (Router 16 here) should do "local repair".
  Any router/LSR which has sufficient information can do
  local repair (for example router 15 or 14 etc)
 
-> Secondly Router 16 can reroute avoiding Router 17, only when
-> Router 17 is not an explicit Hop to be reached from Router 16 for
-> the rerouted LSP

  Not necessarily true. If one of the links between Router 16
  and Router 17 fails, the _only_ requirement is to avoid the
  failed "link" and not the complete "node" (Router 17 here).

  So Router 16 can locally route the LSP to another parallel
  link to Router 17 _OR_ another disjoint path to 17. What you
  are trying to achieve here is link disjointness and not
  node disjointness.
  
-> W.r.to your questions, If Router 16, has indicated the ingress
-> and done the reroute (global repair), It will not indicate the
                                           ^^^^^
-> ingress to reroute again when the link between 16 and 17 comes
-> up.

  Router 16 MAY indicate the ingress LER when the link between
  Router 16 and 17 comes back up. There are no hard and fast rules...

--Venkata Naidu