CCIE Pursuit Blog

May 28, 2009

Core Knowledge Question of the Day: 28 May 2009

Which markings are trusted by default on the interface when you configure the following on a Cisco 3560 switch:

SW1(config)#int f0/1
SW1(config-if)#mls qos trust

Highlight for answer: If no keyword is specified when the command is entered, then DSCP markings are trusted by default when the ‘mls qos trust’ interface-level command is configured.


  1. well i think when u put this command u trust layer 2 markings the cos which is coming on that port for example if ip phone is connected on that port it will mark voice traffic with cos=5 and the switch will trust that value and give voice traffic priority without reclassification and marking ,thats all i know hope it helps

    Comment by skoko — May 31, 2009 @ 4:01 pm | Reply

  2. sry i read about it i think i should say a more detailed view
    mls qos trust has many options incase we trust cos the switch will use the incoming cos to get internal dscp value with cos to dscp map and if we put
    mls qos trust device cisco phone this case the port will only trust cos if a cisco phone is attached and port learns about this using cdp
    other option for mls qos trust dscp which trust dscp valune on ingress and doesnt change it and its is used as the internal dscp and the egress dscp incase we didnt remark in the middle ,also there is option mls qos trust cos dscp pass through which means pass the dscp without any change in it

    Comment by skoko — May 31, 2009 @ 5:41 pm | Reply

RSS feed for comments on this post. TrackBack URI

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

Create a free website or blog at

%d bloggers like this: