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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