QOS on Catalyst 2960

[siddiqirf]

Qos is good in theory, but a pain in practice. please help

I have a 2960 Catalyst switch with LAN Base.I have set my inbound cos value to be a configurable value of cos 3 on fa0/2 (to mark all inbound frames). I understand from Cisco documentation, that this COS value will not be written into the Ethernet frame, but used to derive an "Internal" DSCP value or QOS Label if you will. This internal DSCP is derived from the COS-DSCP map, which in my case maps Cos3 to DSCP 24. (cs3)

This internal DSCP value of 24 should then be written  back to a COS value if the outgoing interface is a trunk based on the DSCP-COS Map. In my case which is using the default mapping of DSCP 24 being mapped to Cos 3. However when I run a packet capture on the outgoing interface, I do not see the frame marked (written) with Cos 3.

Below is my configuration, please can you advise....

mls qos map cos-dscp 0 8 16 24 32 46 48 56

mls qos

!

interface FastEthernet0/1

switchport mode trunk

!

interface FastEthernet0/2

switchport access vlan 100

mls qos cos 3

mls qos cos override

My second question is that if I wanted the internal DSCP of 24 to be written to the IP packet on the outbound, how can I do this?

[manju.cisco]

Pls add "mls qos trust cos" command to Fa0/1.

[siddiqirf]

Thanks its working now.

[manju.cisco]

Hi siddiqirf,

Pls let us know how it started working......so that we can understand it better

Thanks,

Pls rate useful post and mark topic as answered

[siddiqirf]

The packets where always being marked. I didnt need the "mls qos trust cos" command only "mls qos cos 3"

The problem was in the SPAN mirroring interface, which wasnt reading Vlan headers. I had to tweak the windows machine to allow Vlan headers on its NIC card.

[Talha Ansari]

May we know as what tweak was done on the windows machine?

Were you using Wireshark or any other packet capture tool?