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David Kondicz


Hi all,

i need help with QOS in our new network. We have connected 2 cities together with 700Mbit leased line. On each side we have Catalyst 2960S switches and between them is TRUNK for VLAN 10 and Vlan 20.

Vlan 10 is for IPTV (fixed 400 Mb/s for CATV)

Vlan 20 is for Internet (rest).

Sometimes is happening that Vlan 20 takes more than 400 Mb/s for a few seconds and in this situation we have problems with CATV.

Is there any way to make a guaranteed bandwidth 410 Mb/s for CAT - VLAN 10  on this swithces?

Or is there any way to solve this situation with this devices?

Thanx for all!




Hi David,

You can use police for rate limiting your network traffic.

Something like this

ip access-list extended ACL_VLAN10

permit ip any any

class-map match-all ACL_VLAN10

match access-group name ACL_VLAN10

policy-map POLICY_VLAN10

class CLASS_VLAN 10

   police 8000000 8000 exceed-action drop (

Here 8k is the burst bandwidth if vlan 10 consume its allocated bandwidth)

interface xxx

service-policy input POLICY_VLAN10

attached a qos document ,hope this will help you.

Please rate this helps.


Joseph W. Doherty
Hall of Fame Expert


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One simple approach would be to police VLAN 20 traffic at 300 Mbps.  However, this would preclude VLAN 20 from using bandwidth not being used by VLAN 10, and it might still interfere with VLAN 10 if it has a short burst that needs more than 400 Mbps.  A better approach . . .

Is the 700 Mbps using a gig Ethernet interface?  If so, first you want to "shape" for 700 Mbps, and then prioritize your traffic so that your CATV always obtains the bandwidth it needs.

To "shape"a 2960-S gig por for 700 Mbps, use the interface command "srr-queue bandwidth limit 70".  NB: as the port limiter is inexact, you might need to use a lower value.

The 2960S supports 4 hardware egress queues.  To enable them, you need to activate QoS using the global command "mls qos".

With the 4 egress queues active, you need to "map" VLAN 10 traffic into one queue and VLAN 20 traffic into another queue.  Once that's done, you'll also need proportion the 700 Mbps bandwidth between the two VLANs so that VLAN 10 is guaranteed at least 4/7%.  (NB: As video tends to be bursty you may also need to increase buffering allocation for VLAN 10 and/or provide it slightly more bandwidth.)