Subject: Route Pinning

From: [email-masked]
Date: Mon, 20 Dec 1999 15:37:25 +0100

I didn't understand what "Route Pinning" (CR-LDP) is.
Anybody can help me?
Thanks,
            Riccardo.

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From: Robert Raszuk <[email-masked]>
Date: Mon, 20 Dec 1999 16:03:24 -0800

Riccardo,

I don't know much about CR-LDP, but route pinning concept is the same
weather you are using RSVP for tunnel signalling or any other te
signalling protocol. It is basically to pin down the dynamically
selected path so in the future you can enforce the same exact path by
using an explicit path option. 

In RSVP we are using an object called "Record Route" [RRO] to give you
the current list of nodes your tunnel is traveling via to be used later
in the explicit path node list.

R.

> [email-masked] wrote:
> 

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From: "Peter Ashwood-Smith" <[email-masked]>
Date: Tue, 21 Dec 1999 10:02:35 -0500

> > I didn't understand what "Route Pinning" (CR-LDP) is.

   When you explicitly route with CR-LDP you have two options.
You can fully specify the path unambiguously from the source
to the destination, or you can leave some segments as "loose".
When a segment is "loose" it means the intermediate routers 
may fill in parts of the route which are unspecified. Usually
this means just using IP's current shortest path.

   For example if you specify a route as A,B,C,D where the
hops are all strict (i.e. not loose) then you either get the 
route A,B,C,D or you fail to establish the LSP.

   If, on the other hand, you specify a route A,C',D where the
C' is a loose hop, then you may get the route A,B,C,D if 
A decides that B is a good way to get to C. Or possibly some
other intermediate node.

   If at the time the route is established you do get the route
A,B,C,D and a new better route A,Z,C,D becomes available later
on, then your requested route A,C',D can be satisfied with
this new route by moving the A,B,C,D route to the A,Z,C,D
route. 

   It is expected that if you specify a route in a loose fashion
you will probably want it to move around to stay on the best
route within those loose segments. However, moving a route may
cause interruptions in service or, in the case where you have
large numbers of LSPs, may prove to be time consuming.  The
"pin" option allows you to suppress this dynamic behaviour. In 
effect, when you "pin" a "loose" route, you are allowing the
routing system the decision of how to route that segment, but
once it has been established you are asking that the route
stay the same for ever.

    Hope this helps,

    Cheers & Merry Christmas,

    Peter Ashwood-Smith