Franco,
Loop protect provides a more reliable Spanning Tree topology. Normal Spanning
Tree protocol exchanges only a few packets between link partners and then
settles down to a state where BPDUs flow in one direction over the link. When
you enable Loop Protect the switch expects and requires that the link partner
run Rapid or Multi STP. The link will not transition to forwarding until STP
protocol is being exchanged. In addition Loop Protect forces the link partner
to regularly exchange protocol. Doing so ensures the link is not asymmetrical
(broke wire or electronics in one direction). It also ensures that both this
system’s and the link partner’s path for processing STP packets is functional
and that the STP state machine tasks are receiving acceptable amounts of CPU.
Imagine a switch whose STP task gets stuck or does not respond for extended
periods of time. Switches around it may transition their ports from blocking
to forwarding resulting in a loop. In another scenario where the path is
asymmetrical, normal STP operation could place the link in forwarding. In some
cases traffic would be lost going in the failed direction, in others a
redundant link would also go into forwarding and a loop would be formed.
Some older FW and products may not support the protocol feature used to force
the regular exchange of BPDUs. These systems are not compatible with Loop
protect. Compatible link partners do not need to support the Loop Protect
feature although enabling Loop Protect at both ends of the link with two LP
capable switches provides additional protection against failure.
We recommend you enable loop protect on every inter switch port connected to a
compatible or capable link partner. You should never enable LP on ports that do
not run compatible STP protocol.
Dave,
Please open a case with GTAC/support for the problems you
experienced with LP. We would like to understand the cause of issue.
Thanks,
Ernie Eaton
Director of Engineering
N/S/K Series Firmware
Enterasys Networks
From: David Keesman [mailto:[email protected]]
Sent: Wednesday, August 17, 2011 2:26 AM
To: Enterasys Customer Mailing List
Subject: Re: [enterasys] Rstp and loop protect
We've just disabled lp on all our switches (N-series) as it was able to isolate
a N-chassis by disabling both uplink connections towards the core. No lp for us
(maybe it is firmware issue?)...
On Wed, Aug 17, 2011 at 12:18 AM, <[email protected]<mailto:[email protected]>>
wrote:
Hi,
What is the advantage of using loop protect, or what is the risk of not using
it?
Should I activate lp on every switch and on every ISL?
Topology:
S1(root)
|| | | |
|| | | |
lag S3 S4 S5
|| | | |
|| | | |
S2(backup)
Regards,
Franco
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