QOS COS

Unanswered Question
Mar 19th, 2009
User Badges:

I want to make sure i have this correct:


lets say a 3560 switch here:

mls qos is enabled, nothing else.


packet comes in at cos 5.. it will get rewritten to 0. The reason it is 0 is because the mls qos cos 0 command which is default. If i change this command to mls qos cos 1 then all packets would be cos 1. Correct?


Adding to above scenario. If i do mls qos trust cos.. all cos packets coming in at 5 will remain at 5. All packets coming in unmarked will get changed to cos 1. Is this correct?


Building on that. If i now do mls qos override. ALL Packets will get changed to cos 1.


Am i wrong in any of my above understanding?

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Loading.
Jon Marshall Wed, 03/25/2009 - 17:09
User Badges:
  • Super Blue, 32500 points or more
  • Hall of Fame,

    Founding Member

  • Cisco Designated VIP,

    2017 LAN, WAN

Mike


"The reason it is 0 is because the mls qos cos 0 command which is default"


Correct.


"If i change this command to mls qos cos 1 then all packets would be cos 1"


Yes, correct again. By using this command you have changed default value of a port to be Cos 1. So any untagged packets will have their value set to Cos 1.


"Building on that. If i now do mls qos override. ALL Packets will get changed to cos 1"


Yes, correct again.


Your understanding is spot on.


Jon




greg.loria Tue, 04/21/2009 - 01:45
User Badges:

Hi Jon, are these the same with dscp?


We are having trouble with our present setup:


We have two 4500 switches, A and B that are connected by a trunk link. The packet leaves Switch A with a mark of QoS 5 but the value returns to default after passing through the link. Why do you think this issue occurs even though qos trust dscp is configured?


Thanks.

Actions

This Discussion