Cisco Miscellany

interface FastEthernet2/0/1
 switchport trunk encapsulation dot1q
 switchport trunk native vlan 100
 switchport mode trunk
 switchport voice vlan 2
 srr-queue bandwidth share 10 10 60 20
 srr-queue bandwidth shape 10 0 0 0
 mls qos trust cos
 auto qos voip trust
 spanning-tree portfast trunk

What does this mean?

Interface (port) running at 100MBs of identity Switch 2 / Stack 0 ?? / Port 1 has the following characteristics:

It is a trunk and its encapsulation is 802.1Q. Its native to VLAN 100 but will accept traffic from other VLANS too. It is configured to handle traffic from VLAN 2 (i.e. VOIP devices) differently that other traffic. This is shown with the bandwidth shaping and bandwidth sharing.

Each interface has 4 queues (this is known as egress queuing). You can specify what share of the bandwidth by issuing it a ratio of the total bandwidth. So srr-queue bandwidth share 10 10 60 20 would assign 60% of the bandwidth to queue 3.

The shaping command works differently as it denotes a percentage. Queue 1 in the output above will only be able to use 10% of the bandwidth.

The lines containing QoS relate to prioritising the VOIP traffic. The COS identifier (a value originating from the header of frames) is used to identify VOIP traffic which is then given priority over data frames.


It looks as though the VOIP traffic uses queue 1 because it is shaped and allows for "smoother" traffic flow.

Useful links:

https://supportforums.cisco.com/thread/165677