> From: Mark Tinka [mailto:mark.ti...@seacom.mu]
> Sent: Monday, July 09, 2018 11:54 AM
>
>> On 9/Jul/18 11:58, adamv0...@netconsultings.com wrote:
>> That is faulty fibre causes BGP session problems but not targeted-LDP
>> session problems?
>
> Faulty fibre will affect any control plane sessions.
Well that really depends on the type of fault, let me explain:
Fault A) flapping rate is within the dampening reuse limit of the core
interface so the link stays down.
In a network where there's redundancy between two edge PE nodes.
A failed fibre somewhere in the network should not affect just any control
plane protocol.
Quite the opposite.
Does it affect IS-IS or LDP "sessions" (more appropriately adjacencies) yes it
does.
But does it affect BGP or targeted LDP (basically TCP)sessions between the two
edge PE nodes -or BGP session from PEs to RRs? -no it should not (if there's
redundancy in the network).
And by the same token it should not cause downtime on the PW between the two
edge PEs (if there's redundancy in the network)
-yes the PW will now be routed via an alternate path circumventing the faulty
fibre but it will remain UP (unless bound to a TE path forcing it to stay and
fail) and if the switchover is based on FRR customer should hardly notice
anything.
Fault B) flapping rate is outside the dampening reuse limit of the core
interface so the link goes up and down in dampening reuse time intervals.
This is a nasty one, how nasty depends on your interface state dampening scheme.
But with FRR it should be just inconvenience without much effect to customer
traffic carried by the PW that keeps on constantly switching paths, (maybe
resulting in some out of order packets if primary and backup paths are not
symmetric).
Fault C) link never fails,
It exhibits very high packet drop rate to screw your SLAs but not high enough
to take bfd session down (affecting 3 hellos in a row).
Maybe the remedy for this one could be LFM sessions instead of BFD if your
network suffers from low quality fibres -as LFM should take into account Frame
and Symbol error count for all data passing through the interface not just LFM
PDUs, which you can then use as a threshold to bring the link down.
adam
netconsultings.com
::carrier-class solutions for the telecommunications industry::
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