2

I'm looking to implement QoS for VoIP traffic using DSCP tags: EF & AF31.

LLQ for VoIP:

ciscoasa(config)# class-map cm_voip
ciscoasa(config-cmap)# match dscp ef
ciscoasa(config-cmap)# match dscp af31
ciscoasa(config)# policy-map pm_voip
ciscoasa(config-pmap)# class cm_voip
ciscoasa(config-pmap-c)# priority
ciscoasa(config-pmap-c)# service-policy pm_voip global

Police inbound traffic (non-VoIP):

ciscoasa(config)# class-map cm_data_inbound
ciscoasa(config-cmap)# no match dscp ef
ciscoasa(config-cmap)# no match dscp af31
ciscoasa(config)# policy-map pm_data_inbound
ciscoasa(config-pmap)# class cm_data_inbound
ciscoasa(config-pmap-c)# police input cir 98
ciscoasa(config-pmap-c)# service-policy pm_data_inbound interface outside

Shape outbound traffic (non-VoIP):

ciscoasa(config)# class-map cm_data_outbound
ciscoasa(config-cmap)# no match dscp ef
ciscoasa(config-cmap)# no match dscp af31
ciscoasa(config)# policy-map pm_data_outbound
ciscoasa(config-pmap)# class cm_data_outbound
ciscoasa(config-pmap-c)# shape output average 98
ciscoasa(config-pmap-c)# service-policy pm_data_outbound interface outside

Will this essentially reserve 2% of the physical interface's bandwidth for VoIP traffic?

-Thank you

2

Usually, you want to police the priority queue (VoIP). Give it a guaranteed minimum bandwidth, and police everything above that bandwidth. Not policing the priority queue lets the priority traffic end up in non-priority queues, too, and that part of the traffic could get stepped on by non-priority traffic. That causes problems with call quality.

If you are using the outbound interface a line speed, then you shouldn't shape on it. If you are using a sub-rate service, then you should shape to something less than your services rate. How much lower depends on your packet size. VoIP uses very small packets, so the packet overhead is large. If you have a lot of VoIP traffic, then you want a larger difference between the shape rate and the service rate.

What you really want to do is to have a comprehensive, consistent QoS policy across your network. Mark traffic as close to the source as possible. Preferably, on the access switch, but usually do not trust host markings. Most traffic should be left at BE, but you want voice and video to be priority, and you want things like server backups to be treated the worst.

I noticed that you are trying to include AF31 in the VoIP, but that is a mistake. AF31 is control traffic, and it should be treated as such.

Below is a sample that works on Cisco routers. You need to adjust queue sizes and shaping rates for your bandwidth service level:

class-map match-any VOICE
  match ip dscp cs4 cs5 ef
class-map match-any VIDEO
  match ip dscp af41 af42 af43
class-map match-any CONTROL
  match ip dscp  cs3 af31 af32 af33 cs6 cs7
class-map match-any BUSINESS
  match ip dscp cs2 af21 af22 af23
class-map match-any BULK
 match ip dscp cs1 af11 af12 af13
!
policy-map QUEUING-POLICY
  class VOICE
    priority percent 20
    police cir percent 20 conform-action transmit exceed-action drop
  class VIDEO
    bandwidth remaining percent 15
    police cir percent 15 conform-action transmit exceed-action drop
  class CONTROL
    bandwidth remaining percent 10
    queue-limit 2822
    random-detect dscp-based
    random-detect dscp 56 1410 1411
    random-detect dscp 48 1410 1411
    random-detect dscp 24 1057 1058
    random-detect dscp 26 705 1057
    random-detect dscp 28 564 1057
    random-detect dscp 30 423 1057
  class BUSINESS
    bandwidth remaining percent 20
    queue-limit 5640
    random-detect dscp-based
    random-detect dscp 16 2819 2820
    random-detect dscp 18 2115 2820
    random-detect dscp 20 1410 2115
    random-detect dscp 22 705 1410
 class BULK
    bandwidth remaining percent 5
    queue-limit 352
    random-detect dscp-based
    random-detect dscp  8 175 176
    random-detect dscp 10 132 176
    random-detect dscp 12 88 132
    random-detect dscp 14 44  88
 class class-default
    bandwidth remaining percent 50
    queue-limit 8192
    random-detect dscp-based
    random-detect dscp 0 2048 4096
!
policy-map SHAPING-POLICY
  class class-default
    shape average <RATE> <BC>
    service-policy QUEUING-POLICY
!

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