Hi Dave,
thanks for your response. You said, that secondary path + fast reroute is
the fastest option.
But why should I establish a secondary path when I use fast reroute?
As I understand fast reroute each LSR on the path computes his own detour.
When I configure a secondary LSP and the primary fails, the secondary
becomes active. And if the seconadary fails too fast reroute will be used.
Am I wrong ?
Carsten
> -----Ursprüngliche Nachricht-----
> Von: Dave Humphrey [mailto:dave.humphrey@telindus.co.uk]
> Gesendet: Montag, 1. Juli 2002 18:34
> An: 'Strahler, Carsten'; juniper-nsp@puck.nether.net
> Betreff: RE: MPLS redundancy - fast reroute or secondary path
>
>
> There are various options which increase speed of recovery
> but require more
> state to be retained.
>
> Secondary LSP's can be configured to back-up a Primary, the
> secondary LSP's
> can be pre-signalled or not. Pre-signalling cuts down on the
> time it will
> take traffic to switch to the secondary because it will
> already be up. the
> downside is that the routers on the secondary path will have
> to maintain
> "state" for an LSP which is not being used. State ikn the
> case is the RSVP
> traffic (mainly refreshes) to maintain the LSP.
>
> Fast reroute in Juniper terms should be the quickest way of
> recovering from
> LSP failure. Each node in the path calculates a detour around it's
> downstream neighbor which will kick in if that neighbot
> dissappears. When
> the failure is detected the node doing the rerouting will
> signal back to the
> ingress LSP that fast reroute has been invoked and the
> ingress LSP can then
> make its own decision about re-routing the LSP.
>
> If you configure a primary LSP reversion will always take
> place at least
> once. To avoid this configure two secondarys rather than a
> primary and a
> secondary. With this set-up there is no primary LSP to revert
> to. Just make
> sure that the path you want to use first is the secondary you
> configure
> first.
>
> To summarise:
>
> Primary no secondary = slowest. (Primary will recover via IGP
> if possible)
> Primary and non standby (non pre signalled) secondary = Next slowest.
> Primary and standby secondary )pre signalled) = A bit faster
> than above.
> Primary and standby secondary with fast reroute = fastest.
>
> If reversion is not wanted then configure no primary and two
> secondaries.
>
> Dave
>
> -----Original Message-----
> From: Strahler, Carsten [mailto:Carsten.Strahler@lambdanet.net]
> Sent: 01 July 2002 17:14
> To: juniper-nsp@puck.nether.net
> Subject: MPLS redundancy - fast reroute or secondary path
>
>
> Hi,
>
> to minimize the paket loss when a LSP fails Juniper provides
> two mechansim -
> fast reroute and secondary path.
> What are the pro and cons of both ? Are they revertive ?
>
> Thanks
>
>
> ------------------------------------------------------------
> Carsten Strahler
>
> IP Planning
>
> Lambdanet Communications GmbH (AS 13237)
> web: www.lambdanet.net
> -----------------------------------------------------------
>
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