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QoS 3750 switch port trust



We have QoS configured throughout the company, but the standard config we have applied across the 3750 switches only includes the below:

int f1/0/1

sw acc vlan 501

sw acc voice vla 601

priority-queue out   <<<<<<<


We have IP phones (not cisco) attached that are marking with EF, and the PC is an untrusted end device (so needs to be by default marked as zero).

Is the above enough to trust VOIP DSCP EF without resetting it to DSCP 0, or do I also need to add a trust line (i.e.: mls qos trust dscp)?



2 Replies 2

Joseph W. Doherty
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If you both want to not trust an attached PC (vlan 501?) but want to trust a VoIP phone (vlan 601), you could configure the port to use a vlan based policy, then not trust anything on vlan 501, and trust typical VoIP markings on vlan 601.

Or, you might have port policy that accepts just VoIP markings but with a rate-limiter for those markings (about 128 Kbps for bearer and maybe about 32 Kbps for signaling).


Hi Phil,

you can use somthing like this

we using this config with non cisco phone and works fine.

interface FastEthernet0/4

description DATA+VOICE

switchport trunk native vlan 501 (your data vlan)

  switchport mode trunk

switchport voice vlan 601(voice vlan )

srr-queue bandwidth share 1 30 35 5

priority-queue out

mls qos trust device cisco-phone

mls qos trust cos

hope this will help


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