LAN QoS Advice

[Carlos Aguinaldo]

Hello Team,

We are about to migrate our Avaya phone system to Cisco 9.1 in on of our locations. Most of our switches there are old (3750 stacks w/ IPServices running 12.2(25) code). All phones will be replaced with a 8841 IP phone which will connect to our CUCM cluster via our MPLS. The site will have its own VG.

Currently, MLS QoS is used in the switch infrastructure to mark traffic from the Avaya phones. Sample access port (VLAN 120 is voice and VLAN 1 for data).

interface FastEthernet1/0/3
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,120
switchport mode trunk
switchport nonegotiate
srr-queue bandwidth share 10 10 60 20
srr-queue bandwidth shape 10 0 0 0
priority-queue out
mls qos trust cos

Cos-dscp map:
cos: 0 1 2 3 4 5 6 7
--------------------------------
dscp: 0 8 16 26 32 46 46 56

The question, once migrated to the Cisco phone system, should I switch to MQC instead or retain the MLS config? Or, should I use AutoQoS?

I know that the switches' code versions are quite old, but I believe they do support MQC.

Thanks in advance.

[Joseph W. Doherty · Accepted solution]

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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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Posting

If your MLS config is working fine for you, it likely will work for your Cisco phones too.  For Cisco phones, you might consider switching your trust to DSCP rather than CoS.

Unless your service needs match the AutoQoS model, enabling it would probably be inadvisable.

BTW, where did you see MQC for 3750s?

[Carlos Aguinaldo]

Thanks Joseph. Is there really a significant impact if I don't switch to DSCP?

I referred to the following for MQC on 3750s.

http://www.cisco.com/c/en/us/support/docs/switches/catalyst-3750-series-switches/91862-cat3750-qos-config.html#concept22

[Joseph W. Doherty · Accepted solution]

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 wha2tsoever (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

Is there really a significant impact if I don't switch to DSCP?

No, it's just DSCP doesn't rely on a VLAN header tag being present.  Generally a better choice, when you can use it.  (Traditionally, L2 only switches couldn't example L3 packet header info.)

Ah, ok, about 3750 MQC.  That's for defining ingress service policies, when you want to do more than just trust an ingress marking.  Doesn't work with egress on those platforms.  Also, a limited feature set compared to most routers.

So, yes, stick with MLS.

[Carlos Aguinaldo]

Thanks Joseph. Last question though, if I'm not mistaken, all Cisco Phones mark voice traffic at BOTH L2 (RTP as CoS 5 and signalling as CoS 3) and L3 (RTP as DSCP 46 and signalling DSCP 24), correct?

[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 wha2tsoever (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

I'm not 100% certain, but I believe that's the default.  I also believe you can reconfigure for other markings.  For example, many will also mark VoIP signalling with CoS/DSCP 5/EF (not that I'm recommending that).

[Carlos Aguinaldo]

Just went through the link I shared and it seems that outbound policing is not supported on the 3750s. So I might just stick with MLS. What do you think?