3750 QoS on uplink port only

Answered Question
Mar 23rd, 2010

All,

We're bringing a location over into our corporate environment and they're going to be using Avaya phones. The user workstations will be connected into the phone and the phone will be connected into a Dell switch. The Dell is uplinked to the 3750 on port g4/0/26. I've changed the native vlan on the Dell to 95 and I set the native on the 3750 to 95. The phones come over VLAN 10. Everything works as expected to this point.

I now need to set up QoS on the 3750. Can I just create class-maps that match the subnet and ports to assign EF for the phone subnet, or do I need to do something with L2 CoS also? This will actually be the first time that I've set up a L2 QoS config.

Thanks,

John

Correct Answer by Collin Clark about 6 years 11 months ago

I assume you're running at least 100MB so I doubt you'll need to prioritize. If you're looking something quick and dirty, you can use AutoQoS.

mls qos trust means that the port will trust the markings that come through on the packet. It's useful for when the phone marks the traffic. Here's an example (from a 4500) on setting the priority~

interface FastEthernet2/5
...

...

auto qos voip trust
tx-queue 3
   bandwidth percent 33
   priority high
   shape percent 33
service-policy output autoqos-voip-policy

The QoS Campus SRND is excellent and covers LAN QoS and covers everything in depth.

http://www.cisco.com/en/US/partner/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoSDesign.html

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Collin Clark Tue, 03/23/2010 - 06:47

HI John-

The phones should be tagging the packets EF already. On the 3750 you can trust the markings and they will remain intact. Are you looking to prioritize on the uplink(s)?

John Blakley Tue, 03/23/2010 - 06:59

Hi Collin,

I was going to prioritize on the uplink if needed. The topology is like:

Floor 4 - Dell Switch - Avaya phone switch - Connects to Floor 5

Floor 5 - Cisco 3750

Floor 2 - Dell Switch connects to floor 5

The users on Fl 2 will use phones that have to connect to floor 4 through the Cisco. I've got the vlans configured for every switch. There won't be any traffic going outside of this building from the VoIP side (nothing traverses the wan link). So, I'm not sure how important prioritization would be since it's not leaving the location.

Oh, and by priority, do you mean with the "mls qos trust" command?

Thanks,

John

Correct Answer
Collin Clark Tue, 03/23/2010 - 07:23

I assume you're running at least 100MB so I doubt you'll need to prioritize. If you're looking something quick and dirty, you can use AutoQoS.

mls qos trust means that the port will trust the markings that come through on the packet. It's useful for when the phone marks the traffic. Here's an example (from a 4500) on setting the priority~

interface FastEthernet2/5
...

...

auto qos voip trust
tx-queue 3
   bandwidth percent 33
   priority high
   shape percent 33
service-policy output autoqos-voip-policy

The QoS Campus SRND is excellent and covers LAN QoS and covers everything in depth.

http://www.cisco.com/en/US/partner/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoSDesign.html

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