Confused with QOS

Unanswered Question
Jan 19th, 2009
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Within our network, we have QOS enabled on the WAN. However, I've noticed with the snmp management class that we police the SNMP management traffic to 8000k but what happens if we exeed this amount ? It doesn't get dropped as there is no drop policy and the exeed option is only to remark to IP Prec 6. So, I am a bit unsure of what actually happens?

Can someone clear up my confusion?



policy-map LL_serial0/0/0_output

class ce_mgmt_bun_output

police 8000 8000 8000 conform-action set-prec-transmit 6 exceed-action set-prec-transmit 6

bandwidth 8


random-detect exponential-weighting-constant 3

random-detect precedence 0 20 32 10

random-detect precedence 6 20 32 10

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Overall Rating: 5 (1 ratings)
Joseph W. Doherty Mon, 01/19/2009 - 04:26
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On the face of it, it looks like the police statement is pointless since both the conform and exceed actions are identical. However, some policers also support a violate action; unsure whether there's one in action in your case and don't recall what its default action would be. I.e., its possible an active violate might drop packets.

Also, I've sometimes used similar configurations to obtain additional stats. The policer stats will show volume for both conform and exceed actions, so even if we're not actively treating these two actions differently, we can obtain information on that class's traffic load usage.

Giuseppe Larosa Mon, 01/19/2009 - 14:32
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Hello Mary,

this kind of configuration can be used for marking all traffic of this class with IP Precedence 6 with no real policing action.

And I think the idea is to provide the correct marking in any case, but as Joseph suggests this policy map can say over time how much traffic is over 8000 bps (exceed traffic) so provide some info on the snmp traffic peaks.

Hope to help



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