7600 QoS and Policing

[Andre Grove]

Hello all,

I've been reading up on how to do QoS on a 7600, which fromthe looks of things is not so simple.

The reason I'm looking into this, is because I have an interface policed at 30mb for all traffic. What I'd like to do is prioritise VoIP traffic.

From my "research" and attempts, I realise you can't do MQC, so this is how I think I can achieve my goal. I'm only interested in the interface that has the policer applied for now.

• Map traffic to appropriate CoS value
• I'll mls qos trust dscp on the source interfaces and make sure that EF is mapped to CoS5

• On the egress interface with the policer, do priority-queue cos-map 1 5 6 7
• That gets traffic into the strict-priority queue. Easy enough.
• This is where it gets a little funky for me
• With the 30mb policer on, all traffic will contend for the bandwidth. If some naughty traffic with CoS5/6/7 comes along, it could bump all the other traffic off the interface.
• This is what I think I need to do:

policy-map FOO
class RPs
class VoIP
police cir 6000000
conform-action transmit
exceed-action drop
violate-action drop
class class-default
police cir 24000000
conform-action transmit
exceed-action drop
violate-action drop

The RP class is just looking at OSPF traffic - I want to leave that alone. Then I police the VoIP traffic before(?) it goes the strict priority queue. Then police everything else.

There are a few fundamentals that I don't quite understand. I was always under the impression that QoS only gets applied under congestion. Will the interface know it's congested at 30mb on a 1gb interface, or do you have to set the bandwidth statement on the interface?

Any insight would be appreciated. I'm really enjoying working on this; I've not really done QoS work before. Wish I could have picked a simpler platform to start with though.

[Joseph W. Doherty]

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Posting

I was always under the impression that QoS only gets applied under congestion.

Depends on the QoS.  Congestion based QoS does rely on congestion to trigger it.

Will the interface know it's congested at 30mb on a 1gb interface, or do you have to set the bandwidth statement on the interface?

Normally no and no.

On full featured routers, shapers are used to create congestion before the physical interface would.  However, some line cards might support shaping on the 7600.  I recall the FlexWANs did, and maybe some of the ES cards do too.

[Andre Grove]

Thanks for that.

I found this page that seems to indicate my idea of policing traffic that gets mapped to the strict-priority queue might work (see QoS Flow in the Catalyst 6500):

http://www.cisco.com/c/en/us/products/collateral/switches/catalyst-6500-series-switches/white_paper_c11_538840.html

I know it's for 6500, but I think most of the logic still applies. Need to look through that whole page now.