[j-nsp] Bypass LSP functionality question

[Stefan Fouant]

Correction, I said Path Tear in my previous message, rather I meant Path 
Err...

Stefan Fouant
JNCIE-ER #70, JNCIE-M #513, JNCI
Technical Trainer, Juniper Networks
http://www.shortestpathfirst.net
http://www.twitter.com/sfouant

On 7/7/2011 12:15 AM, Stefan Fouant wrote:
> On 7/6/2011 11:50 AM, David Ball wrote:
>> Just looking for confirmation of a suspicion here.
>>
>> If I have an LSP configured with link-protection on every interface
>> along the way (creating many-to-one Bypass LSPs, as opposed to 1:1
>> detours), no secondary standby path defined, and a protected interface
>> fails, the ingress node will have no ability to perform a
>> make-before-break, right? Because the Path Tear messages will be sent
>> both upstream and downstream from the failed interface? The bypass
>> will only help me up until the upstream nodes process the Path Tears
>> and a new LSP is signalled from the ingress node....or am I missing
>> something?
>
> Hi David,
>
> The bypass is only used temporarily to save the traffic that is already
> traversing the LSP. At the same time that the bypass LSP is being used,
> the node which established the Bypass around the failure will will send
> the Path Tear message upstream towards the Ingress LSR.
>
> Once the Ingress LSR receives the Path Tear it may signal an alternate
> path assuming some Secondary paths have been configured. You could have
> the Secondary LSP set up as a Standby in which case it is pre-signaled
> but will require double the amount of reservation state in the network.
> This is inherently make-before-break because the Secondary Standby is
> already established by the time your Primary has failed.
>
> Another option is to configure the Adaptive option which will force the
> Ingress LSR to continue using the Primary LSP (traversing a Bypass)
> until it has signaled the Secondary path and only once the secondary has
> been established will it cease using the Primary. This has the benefit
> of also reducing the amount of reservation state in the network due to
> the fact that Adaptive option signals LSPs using the Shared Explicit style.
>
> HTHs,
>
> Stefan Fouant
> JNCIE-ER #70, JNCIE-M #513, JNCI
> Technical Trainer, Juniper Networks
> http://www.shortestpathfirst.net
> http://www.twitter.com/sfouant
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