QoS DSCP 48

[tedauction]

Hello, I notice via the command 'sh mls qos int x/x/ statistics' that I have DSCP 48 marked traffic passing via my switch.

My question is why would this traffic get placed in queue 2 as per 'mls qos srr-queue output dscp-map queue 2 threshold 3 48 5'.

I thought DSCP 46 and above would be the priority traffic ?

Also, what is generating this DSCP 48 traffic ? is 48 the default tag that Cisco VoIP phones use. I always thought that was DSCP 46

Thanks for any help.

mls qos map policed-dscp 0 24 26 46 to 8
mls qos map cos-dscp 0 8 16 24 40 46 48 56
mls qos srr-queue output cos-map queue 1 threshold 3 5
mls qos srr-queue output cos-map queue 2 threshold 1 2 4
mls qos srr-queue output cos-map queue 2 threshold 2 3
mls qos srr-queue output cos-map queue 2 threshold 3 6 7
mls qos srr-queue output cos-map queue 3 threshold 3 0
mls qos srr-queue output cos-map queue 4 threshold 3 1
mls qos srr-queue output dscp-map queue 1 threshold 3 46
mls qos srr-queue output dscp-map queue 2 threshold 1 16 18 20 22 25 32 34 36
mls qos srr-queue output dscp-map queue 2 threshold 1 38
mls qos srr-queue output dscp-map queue 2 threshold 2 24 26
mls qos srr-queue output dscp-map queue 2 threshold 3 48 56
mls qos srr-queue output dscp-map queue 3 threshold 3 0
mls qos srr-queue output dscp-map queue 4 threshold 1 8
mls qos srr-queue output dscp-map queue 4 threshold 3 10 12 14
mls qos queue-set output 1 threshold 2 70 80 100 100
mls qos queue-set output 1 threshold 4 40 100 100 100
mls qos

[Mark Malone · Accepted solution]

DSCP 48 is control traffic CS6 for voice usually so it shouldn't be in the priority queue , looking at my switches running mls its the same , queue 2

!
mls qos map cos-dscp 0 8 16 24 32 46 48 56
mls qos srr-queue output cos-map queue 1 threshold 3 5
mls qos srr-queue output cos-map queue 2 threshold 3 3 6 7
mls qos srr-queue output cos-map queue 3 threshold 3 2 4
mls qos srr-queue output cos-map queue 4 threshold 2 1
mls qos srr-queue output cos-map queue 4 threshold 3 0
mls qos srr-queue output dscp-map queue 1 threshold 3 40 41 42 43 44 45 46 47
mls qos srr-queue output dscp-map queue 2 threshold 3 24 25 26 27 28 29 30 31
mls qos srr-queue output dscp-map queue 2 threshold 3 48 49 50 51 52 53 54 55
mls qos srr-queue output dscp-map queue 2 threshold 3 56 57 58 59 60 61 62 63
mls qos srr-queue output dscp-map queue 3 threshold 3 16 17 18 19 20 21 22 23
mls qos srr-queue output dscp-map queue 3 threshold 3 32 33 34 35 36 37 38 39
mls qos srr-queue output dscp-map queue 4 threshold 1 8
mls qos srr-queue output dscp-map queue 4 threshold 2 9 10 11 12 13 14 15
mls qos srr-queue output dscp-map queue 4 threshold 3 0 1 2 3 4 5 6 7
mls qos queue-set output 1 threshold 1 138 138 92 138
mls qos queue-set output 1 threshold 2 138 138 92 400
mls qos queue-set output 1 threshold 3 36 77 100 318
mls qos queue-set output 1 threshold 4 20 50 67 400
mls qos queue-set output 2 threshold 1 149 149 100 149
mls qos queue-set output 2 threshold 2 118 118 100 235
mls qos queue-set output 2 threshold 3 41 68 100 272
mls qos queue-set output 2 threshold 4 42 72 100 242
mls qos queue-set output 1 buffers 10 10 26 54

[Joseph W. Doherty]

My question is why would this traffic get placed in queue 2 as per 'mls qos srr-queue output dscp-map queue 2 threshold 3 48 5'.

I thought DSCP 46 and above would be the priority traffic ?

How traffic with different ToS markings is treated is up to your QoS policy.  Under the old IPPrec recommendations, higher values got "better" treatment; also IPPrec 6 was recommended for network control traffic and IPPrec 7 was recommended for network issues.  Generally, under DSCP recommendations, CS6 and CS7 are used the same (as under the IPPrec recommendations).  (NB: some routing protocols mark their traffic with IPPrec 6, I believe Cisco's BGP does, as do some interactive user protocols, I believe Cisco router's telnet also mark IPPrec 6.)

How and when PQ is used, also, depends on your QoS policy.  Generally, PQ is reserved for traffic that needs the very "best" treatment, with the understanding, PQ can starve other traffic of all its bandwidth.  Generally, VoIP bearer traffic is provided PQ treatment.  IPPrec 6 traffic often doesn't really need PQ treatment.  IPPrec7, though, might also merit PQ treatment.

Also, what is generating this DSCP 48 traffic ? is 48 the default tag that Cisco VoIP phones use. I always thought that was DSCP 46

The only way to know for sure what's the traffic using specific markings is to examine the traffic with those markings.  It's true, various vendor VoIP phones use default QoS markings, but it's also true, often those VoIP phones might be reconfigured.

[Gerard Roy]

Would I leave all this the same if I was plugging in an Avaya phone?
What do the interface commands look like? Can you copy and past a single interface so I can review?

[Mark Malone]

Avaya phone should be marking with EF46 but you should confirm this  , if it is you can use mls qos trust dscp on the access port and the uplink and turn on mls globally with mls qos , the Avaya phone should mark it at teh source and the ports will carry the markings with those settings

interface FastEthernet0/8
 switchport access vlan 156
 switchport mode access
 srr-queue bandwidth share 1 30 35 5
 priority-queue out
 mls qos trust dscp
 spanning-tree portfast
 ip dhcp snooping limit rate 7

[Joseph W. Doherty]

"Would I leave all this the same if I was plugging in an Avaya phone?"

That depends on how the Avaya phones are configured to mark and whether those settings are suitable for your QoS requirements/needs.

As Mark mentions, Avaya will likely mark the VoIP bearer traffic DSCP EF. It's a bit of a guess how Avaya VoIP phones will mark its control traffic, as they often recommend also marking it DSCP EF.

"What do the interface commands look like? Can you copy and past a single interface so I can review?"

That depends on the device and the policy that's being implemented.

Many Cisco devices support an auto-QoS command, that will configure your QoS for Cisco's recommended QoS policy (at least at the time that particular platform and IOS were released).

Cisco has a QoS design guide that offers suggested policies for some of their different devices.