QOS question for a cisco 3560x

[john.wright]

We have a small site that has an Avaya voice switch connected to a c3560x switch.

The avaya tech told us to set this on our ports to which the phone and the desktop are connected.

interface GigabitEthernet0/11

description jack 62 viewing area 131

switchport mode access

switchport voice vlan 252

no logging event link-status

speed 1000

duplex full

no snmp trap link-status

mls qos trust cos

spanning-tree portfast

I issued this command on the switch. And I am wondering what it means.

sh mls qos vlan 252

Vlan252

QoS is disabled. When QoS is enabled, following settings will be applied

[nkarpysh]

Hi,

First of all you need "mls qos" command to be applied globally for it to work (though configuring mls qos trust cos on interface Gi0/11 you should have seen warning about it and possibly applied).

Other thing is that port based QoS and Vlan-based are different things. If you applied QoS on port bases - you need to watch it there as VLAN qos will work if port is assigned with "mls qos vlan-based" settings.

Hope this helps,

Nik

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

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In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

The Avaya tech left much unsaid.  Your 3560X will accept L2 CoS or L3 ToS, and pass them along while QoS is disabled (the default).  However, the 3560X won't provide any special treatment to your VoIP, or other marked, frames/packets either.

Once you enable QoS, by default, ports will erase not trusted received L2 CoS or L3 ToS, until the port (or VLAN) is configured to trust or accept them.  The port configuration command given to you is one way to keep the switch from not erasing the CoS when QoS is enabled.

Once you enable QoS, there's usually more involved to correctly treat VoIP packets then just trusting a L2 CoS or L3 ToS on the original ingress port.  For example, L2 CoS is only carried in VLAN tagged frames.  How will/should the L2 CoS be treated beyond its original ingress port?  Are you going to support L2 CoS end-to-end or will there be transitions to/from L3 ToS?  Does it make sense to use L2 CoS at all or just use L3 ToS instead?  How exactly is the Avaya phone going to mark the VoIP bearer frames and packets and the VoIP signally frames and packets?

With your switches not enabled for QoS, they will behave one way, which may or may not be adequate to support your VoIP deployment.  Once you enable QoS, their behavior changes, and the QoS default settings still may or may not be adequate to support your VoIP deployment.  (NB: it's possible that just activation of QoS, with its default settings, can make things worst.)  QoS default settings can be configured to meet your actual QoS needs, but this can be very complex and difficult to maintain.  To bridge the gap between default settings and needing to customize every QoS related setting, many modern Cisco devices support AutoQoS.  AutoQoS provides a "smarter" default configuration; it can also be customized.

Without know much, much more about your network, can't suggest what you should do, but hopefully I've conveyed there's more to supporting VoIP than an individual 3650X port setting configuration.  Besides what the Avaya tech didn't say, what I do see on the port configuration gives me some concern.  For example, it appears the data VLAN may use VLAN 1.  I see a user edge gig port hard coded for speed and duplex.  I don't see PQ set on this port.

[john.wright]

Joseph

Thanks for your reply.

I have little or no knowledge of qos so I was just trying to find out if what we were doing on the switch had any affect on voip traffic.

I did not mention in my first post that we are not routing Voip out the WAN. We have future plans to do that but for now all the traffic goes out a trunk line to the carrier.

If I there is no mls qos global command set on the switch, which there is not, then these settings do nothing? If I understand correctly from your forth paragraph our qos settings are not in factor on our lan because we do not have mls qos set globally.

"How will/should the L2 CoS be treated beyond its original ingress port?"

This is really what I want to know. If there is no voip over WAN what does qos really do for voip traffic on a LAN as I have it configed right now?

"Are you going to support L2 CoS end-to-end or will there be transitions to/from L3 ToS?  Does it make sense to use L2 CoS at all or just use L3 ToS instead?"

Right now we do L3 ToS for four sites via an old Nortel system. These four sites do not use IP phones. The voice traffic has a seperate lan switch and a seperate ethernet connection on the router. The router then routes voip traffic via vendor provided ToS settings between the four sites. These four sites are the only sites that currently have a dial plan with 4 digit dialing.

The other 8 sites are currently not routing Voip over the WAN. Though some of them have an Avaya switch like I mentioned in the original post with Avaya IP phones they all route out the providers trunk and the users have to dial 9 digits to call the other sites. 

"How exactly is the Avaya phone going to mark the VoIP bearer frames and packets and the VoIP signally frames and packets?"

I don't have an answer for this yet. But we are still a few years out before we have a totally intergrated Voip and data network.

Your last paragraph comments

Yes the data is on vlan 1.

The avaya tech told us to hard code the speed and duplex as you see it.

What is PQ?

Thanks for your helpful comments.

John

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

"If I there is no mls qos global command set on the switch, which there is not, then these settings do nothing?"

Correct.

"If there is no voip over WAN what does qos really do for voip traffic on a LAN as I have it configed right now?"

Without mls QoS activation, as above, nothing.  With mls QoS activation, depends on markings of frame/packet and QoS configuration.  Ideally, you want to give 1st priority to VoIP bear traffic and insure VoIP signally traffic has enough bandwidth.

"The avaya tech told us to hard code the speed and duplex as you see it."

I believe autonegotiation is a required part of the gig standard, and if it is, it would be interesting why the Avaya tech told you to do it.

"What is PQ?"

Priority Queue - a feature that gives absolute priority to one of the 3560's four egress queues - normally used for real-time traffic, such as VoIP bearer.