VoIP config on switches with no phones connected

[lcaruso]

Hi,

This particular switch has all ports identically configured but only  has three ip phones connected. I've been asked to find ways to speed up  the existing network as was wondering about this.

Does having the following configuration degrade performance for ports that do not have phones in any way?

Does the priority queue only affected marked voice packets? And if there are no voice packets, then does that delay data packets since it must first check the markings?

Thanks.

mls qos map cos-dscp 0 8 16 26 34 46 48 56

mls qos queue-set output 1 threshold 2 400 400 100 400

mls qos queue-set output 1 buffers 15 45 20 20

mls qos

(all ports identical config)

interface FastEthernet0/1

switchport access vlan 50

switchport mode access

switchport nonegotiate

switchport voice vlan 101

priority-queue out

mls qos trust cos

no mdix auto

spanning-tree portfast

[Reza Sharifi · Accepted solution]

Does  having the following configuration degrade performance for ports that do  not have phones in any way?  - See more at:  https://supportforums.cisco.com/thread/2202800?tstart=0#sthash.LEouTtJc.dpuf

Does  having the following configuration degrade performance for ports that do  not have phones in any way?  - See more at:  https://supportforums.cisco.com/thread/2202800?tstart=0#sthash.LEouTtJc.dpuf

Does  having the following configuration degrade performance for ports that do  not have phones in any way?  - See more at:  https://supportforums.cisco.com/thread/2202800?tstart=0#sthash.LEouTtJc.dpuf

Does  having the following configuration degrade performance for ports that do  not have phones in any way?  - See more at:  https://supportforums.cisco.com/thread/2202800?tstart=0#sthash.LEouTtJc.dpuf

No, it doesn't degrade the performance since the none voice packet use default cos (0).

But if you only have voice connected to 3 ports why have all the extra configs on all the pther ports.  So, on the ports that you don't have any phone connected to remove below configs

switchport voice vlan 101

priority-queue out

mls qos trust cos

Also 

also priority-queue out command is an egress priority queue and usually applies to uplinks and not ports connected to hosts.

HTH

ority-queue out

Does  having the following configuration degrade performance for ports that do  not have phones in any way? - See more at:  https://supportforums.cisco.com/thread/2202800?tstart=0#sthash.LEouTtJc.dpuf

Does  having the following configuration degrade performance for ports that do  not have phones in any way? - See more at:  https://supportforums.cisco.com/thread/2202800?tstart=0#sthash.LEouTtJc.dpuf

[lcaruso]

About it affecting performance, if the priority queue is bound to an egress trunk port, and the markings give data default cos 0, and that is only allocated 15% of the port's available buffers, it seems to potential to degrade data performance is present but only if the interface commands (especially priority-queue out) are left in place.

So removing those interface commands in the case where no phone is present makes a great deal of sense.

Thanks.

[Wilson Bonilla · Accepted solution]

Hi.

This switch is QoS enabled, that means that queues memory allocation is modified, If your switch is pure data flow, and has minimal or nothing voice traffic, you shouldn't be using QoS.

Queues assinged to queue-set1 are limited the following way:

Queue 1 has only 15% of the total interface resources.

Queue 2 as 45%

Queue 3 and 4 has 20% each.

Take at look at the output of show interfaces summary, if you notice ODQ (output drops) it's most likely due to bad qos implementation.

Also verify if qos is really enabled, "show mls qos" can tell you that.

Does having the following configuration degrade performance for ports that do not have phones in any way?

YES!!! Image if everything is pure data flow, most likely by default data traffic is marked with a DSCP value of 0. If so data traffic is mapped to queue 1, and guess what queue 1 only takes advantage of 15% of total interface resources.

Does the priority queue only affected marked voice packets?

It will affected only traffic associated to the priority queue, by default in fixed units priority queue is 1 threshold 1.

And if there are no voice packets, then does that delay data packets since it must first check the markings?

Priority queue is serve first until empty. markings are done during queueing and scheduling and yes it could add delay, if the buffer for non-priority queues are full before the priority queue gets served then the switch will start dropping packets, causing at the same time retransmissions, packet loss, general performance issues and then things start going wrong...

Regards.

Wilson B.

Does  the priority queue only affected marked voice packets? And if there are  no voice packets, then does that delay data packets since it must first  check the markings?

- See more at: https://supportforums.cisco.com/message/3871458#3871458

[lcaruso]

Thanks much for your reply.  A lot of good information there.

If a switch only has 3 out of 48 active ports VoIP, would you enable QoS on the switch then in a LAN setting?

Can you point me to a good link that explains all of these settings and/or QoS setup in general?

[lcaruso]

Take at  look at the output of show interfaces summary, if you notice ODQ (output  drops) it's most likely due to bad qos implementation.  - See more at:  https://supportforums.cisco.com/message/3871788#3871788

Take at  look at the output of show interfaces summary, if you notice ODQ (output  drops) it's most likely due to bad qos implementation.  - See more at:  https://supportforums.cisco.com/message/3871788#3871788

Take at look at the output of show interfaces summary, if you notice ODQ  (output drops) it's most likely due to bad qos implementation. 

I just checked all the switches at this site. They all have QoS implemented and the only one that doesn't have output drops is the one that doesn't have any phones connected.

Seems like you may have something there.

[Wilson Bonilla]

Hello again.

Unfortunately Catalyst QoS can't be explained in general, it differs from platform to platform, from supervisor to supervisor, from linecard to linecard and even IOS makes changes to the way how it's configured, The best I can advise is to check the configuration guides at cisco.com everytime you have a question about qos.

The tittle Cisco Catalyst QoS: Quality of Service in Campus Networks explains a bit of everything; classification, marking and policing, scheduling and queueing, shaping and sharing, weighted round robin and shaped round robin) .....

Regards.

Wilson B.