Thursday, August 12, 2010

Another 3750 Switch QOS article

Hi Guys,


You may have guessed I am studying 3750 QOS at the moment. Certainly an area I need to brush up on! I have spent quite a while studying it, in particular the document in my previous post.

However I found something that you might all be interested in and should potentially keep in mind:

3750's when you apply a policy-map to an int, DON't show any hits against the policy!

Shockingly annoying, since it makes it very hard to troubleshoot:

HQ-SW1#show run | begin policy-map
policy-map mypolicy
class voice_bearer
police 128000 8000 exceed-action drop
set dscp ef
class voice_signal
police 32000 8000 exceed-action policed-dscp-transmit
set dscp cs3

Here is an example of my policy map, I have also applied it to an interface:


HQ-SW1#show run int fa0/3
Building configuration...

Current configuration : 99 bytes
!
interface FastEthernet0/3
description == HQ 7960 IP Phone 1
service-policy input mypolicy
end



But when I do our good friend show policy-map int fa0/3...



HQ-SW1#show policy-map int fa0/3
FastEthernet0/3

Service-policy input: mypolicy

Class-map: voice_bearer (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: ip dscp ef (46)

Class-map: voice_signal (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: ip dscp af31 (26)

Class-map: class-default (match-any)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any
0 packets, 0 bytes
5 minute rate 0 bps



As you can see there are no hits against it! but it is working I assure you.

The only way to really verify is shown below:
HQ-SW1#show mls qos int fa0/3 policers
FastEthernet0/3
policymap=mypolicy

type=Single, id=1 rate=128000, qlimit=8000, drop=1
markdown dscp=0
type=Single, id=2 rate=32000, qlimit=8000, drop=0
markdown dscp=0
HQ-SW1#

At least with this you can see the traffic.

I hope this helps someone out there!

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