[c-nsp] Interruptions when enabling "mls qos"

[Andre Beck]

Hi Peter,

On Tue, May 13, 2008 at 10:28:55AM +0200, Peter Rathlev wrote:
> 
> We're preparing a service window and need to enable this on a few edge
> and distribution units, but we're unable to say exactly how much
> disturbance the network can expect, e.g. if this would down
> eBGP-sessions. Does anybody have any experience in this area?

Another possible source of disturbance might be that enabling just
"mls qos" (without pushing more QoS-related commands) will have the
switches default to TOS *nulling* while they were just transparently
passing the TOS bits before. This can lead to QoS problems on seemingly
unrelated paths that are congested and have proper QoS, but all of a
sudden don't get to see the correct DSCPs any longer.

So push all the relevant "mls qos trust dscp" or whatever commands
you plan to roll out before enabling "mls qos" globally (just in case
you weren't aware of this potential issue).

HTH,
Andre.
-- 
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-> Andre Beck    +++ ABP-RIPE +++      IBH IT-Service GmbH, Dresden <-