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Community Member

Advice on dscp af31 please!

Hi, We have a number of VC units running on 3750's and 3560's using the following QoS policy:

class-map match-all Video_Packets

match access-group name Video_Packets

policy-map Video_Conf

class Video_Packets

set dscp af31

ip access-list extended Video_Packets

permit udp any range 17000 17310 any range 17000 17310

permit udp any range 17000 17310 any range 49000 49310

permit udp any range 49000 49310 any range 17000 17310

permit tcp any range 1700 1750 any range 3230 3235

permit tcp any range 3230 3235 any range 1700 1750

permit tcp any range 1700 1750 any gt 1024

permit tcp any gt 1024 any range 1700 1750

permit udp any host 10.xxx.xxx.xxx

permit udp any host 10.xxx.xxx.xxx

We pay our telco to provide QoS over our WAN circuits but have a doubt that they are actually tagging the packets due to the quality we are experiencing.

Using Wireshark/Ethereal can anyone tell me what to look for (If I carry out a trace) to see if the packets are being marked/tagged?

Any help appreciated.

Josh

Us

4 REPLIES
Community Member

Re: Advice on dscp af31 please!

What do you see when you do "sh policy-map int xxx" and "sh access-list"? Any hits?

What kind of problem that you're experiencing?

Community Member

Re: Advice on dscp af31 please!

I get:

Service-policy input: Video_Conf

Class-map: Video_Packets (match-all)

0 packets, 0 bytes

offered rate 0 bps, drop rate 0 bps

Match: access-group name Video_Packets

Class-map: class-default (match-any)

0 packets, 0 bytes

offered rate 0 bps, drop rate 0 bps

Match: any

0 packets, 0 bytes

rate 0 bps

The Polycom units show packet loss and the picture is always pixelating and refreshing.

It sporadically freezes for a split second then goes out of focus.

The switch port shows no errors whatsoever.

Hope this helps?

Community Member

Re: Advice on dscp af31 please!

Can you also post the router config where the 3750/3560 is connected?

A couple of things that you can try:

1. Change "class-map match-all Video_Packets" to "class-map match-any Viideo_Packets" so that it'll match any parameter in your access-list.

2. Take a look at your Polycom unit. I may be set at "IP Precedence 4" instead of "AF31". If so, change it in your policy-map.

3. Verify that the port speed and duplex are set to "auto" where the Polycom unit is connected in your switch port.

4. Take a look at this document: http://www.cisco.com/en/US/tech/tk1077/technologies_configuration_example09186a0080111c1b.shtml

hth

Super Bronze

Re: Advice on dscp af31 please!

"Using Wireshark/Ethereal can anyone tell me what to look for (If I carry out a trace) to see if the packets are being marked/tagged?"

Look for either a DSCP or IP Precedence decode in the IP packets carrying the video traffic. Ideally, off the link coming off the WAN.

PS:

If your Telco tags the traffic, why are you setting DSCP?

Besides tagging, has the Telco committed to any SLA with regards to bandwidth, latency, jitter and/or loss, for your video traffic?

Who manages the WAN routers and what type of WAN circuits are being used?

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