Voice QoS Configuration

[brmmt1]

Hi, I have tried configuring LLQ to prioritise Voice over the WAN. I have done this on some of our Branch Routers and the queuing seems to be working fine. However, I have introduced the same config on our Core Router and I am seeing dropped packets on the Default Class. I have configured a priority queue for Voice Streams and another queue for Signalling traffic. There is then also the Class-Default which all other traffic will be flowing through. 25 Percent of bandwidth is taken by the Priority Queue and 5% for the Signalling Queue. Any ideas why I am seeing dropped packets in the Class-Default?

class-map match-all VOIP

match access-group 170

class-map match-all SIGNAL

match access-group 171

!

!

policy-map LLQ

class VOIP

priority percent 25

set ip precedence 5

class SIGNAL

bandwidth percent 5

set ip precedence 4

class class-default

fair-queue

!

interface FastEthernet0/0

description WAN

bandwidth 10240

ip address 1.2.3.4 255.255.255.254

ip nat inside

ip virtual-reassembly

load-interval 30

duplex full

speed 10

service-policy output LLQ

!

access-list 170 permit udp any any range 16384 31700

access-list 170 permit tcp any any eq 1720

access-list 170 deny ip any any

access-list 171 permit tcp any any eq 67

access-list 171 permit tcp any any eq 68

access-list 171 permit tcp any any eq 389

access-list 171 permit tcp any any eq 8404

access-list 171 permit tcp any any eq 1700

access-list 171 permit tcp any any eq 1701

access-list 171 permit tcp any any eq 1702

access-list 171 permit tcp any any eq 5000

access-list 171 deny ip any any

sh policy-map

Policy Map LLQ

Class VOIP

Strict Priority

Bandwidth 25 (%)

set ip precedence 5

Class SIGNAL

Bandwidth 5 (%) Max Threshold 64 (packets)

set ip precedence 4

Class class-default

Flow based Fair Queueing

Bandwidth 0 (kbps) Max Threshold 64 (packets)

sh policy-map int fa0/0
FastEthernet0/0

Service-policy output: LLQ

Class-map: VOIP (match-all)
322662 packets, 69065163 bytes
30 second offered rate 89000 bps, drop rate 0 bps
Match: access-group 170
Queueing
Strict Priority
Output Queue: Conversation 264
Bandwidth 25 (%)
Bandwidth 2560 (kbps) Burst 64000 (Bytes)
(pkts matched/bytes matched) 135854/29120086
(total drops/bytes drops) 0/0
QoS Set
precedence 5
Packets marked 322662

Class-map: SIGNAL (match-all)
7108 packets, 2699847 bytes
30 second offered rate 2000 bps, drop rate 0 bps
Match: access-group 171
Queueing
Output Queue: Conversation 265
Bandwidth 5 (%)
Bandwidth 512 (kbps)Max Threshold 64 (packets)
(pkts matched/bytes matched) 2497/1004453
(depth/total drops/no-buffer drops) 0/0/0
QoS Set
precedence 4
Packets marked 7109

Class-map: class-default (match-any)
3058039 packets, 2234596119 bytes
30 second offered rate 8735000 bps, drop rate 49000 bps
Match: any
Queueing
Flow Based Fair Queueing
Maximum Number of Hashed Queues 256
(total queued/total drops/no-buffer drops) 26/5709/0

Any help would be greatly appreciated, let me know if you need any more config/output.

Thanks

[stephen.stack]

I think your drop count is not that excessive at 5709 drops total for the default-class. But you have hard coded your interface for 10Mbps and if I read correctly the policy-map interface output for the default class shows a 30 second rate of 8735000 bps = 8.3Mbps

30 second offered rate 8735000 bps, drop rate 49000 bps

It would appear that your maxing out on the default class from time to time which is causing drops in that class. Is this an over subscribed interface?

Regards

Stephen

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[Joseph W. Doherty · Accepted solution]

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Posting

Those drops are likely due to transient congestion.  (Notice how you had 26 packets queued in class-default when you did the show.)

For 10 Mbps, default queue depths can often "safely" be increased.  See if your default-class will accept a larger queue limit.