mls qos trust dscp is required at access port?

[syjeon]

Hi,

I wonder if we still need to configure 'mls qos trust dscp' at switch access port. the switch is kind of layer 2 function. it currently not enabled 'mls qos' by global command.

I would like to trust dscp value when the packet is passing above L2 switch access port. but it's not configured 'mls qos' and 'mls qus trust dscp'.

[Vinayaka Raman]

you can  also think this way..

Let's say there is an ip phone connected to L2 switch access port..you need to trust the COS value within L2 domain and DSCP or IP precedence value on L3 domain..generally LAN segment will be of larger bandwidth (gig links) and may not suffer congestion..so even if you do not trust COS, it may not lead to trouble over the trunks..however it is best practise to trust COS on L2 domain..

So trusting dscp on access port will ensure the precedence or dscp will be preserved until it reach the destinaton and will be used by layer 3 hops..but it needs to trusted end to end...

there are many experts here, and i may seek some corrections

[syjeon]

Hi, I got your point.

actually, TP device will connect to access port. the diagram is like below.

TP device --- Layer 2(mls qos trust dscp) --- Layer 3( mls qos trust dscp) -- Layer 2(not mls qos trust dscp) --- Router --- WAN

we set and classified TP traffic accodingly on first layer 2 switch.  and it's configured 'mls qos trust dscp) till 2nd switch.

I wonder if 2nd layer 2 switch is still need 'mls qos trust dscp' this is switch what I quired as above.

the configuration likes below.

interface GigabitEthernet1/0/13

switchport access vlan 60

switchport mode access

speed 1000

duplex full

no mdix auto

end

[Vinayaka Raman]

please take a look at

https://supportforums.cisco.com/thread/341950