Re: Ask the Expert: Troubleshooting WAN Links Using QoS - Page 2

ciscomoderator · ‎01-03-2012

Troubleshooting WAN Links Using QoS
with Sarala Akella

Welcome to the Cisco Support Community Ask the Expert conversation. This is an opportunity to learn how to troubleshoot congestion on WAN links by using QoS and buffering best practices to optimize traffic flow. This includes queueing techniques (like WFQ, CBWFQ, or LLQ,) congestion avoidance (like WRED and CAR) as well as policing and traffic shaping mechanisms. Sarala is a customer support engineer at the Cisco Technical Assistance Center. She currently works in the WAN team where she focuses on various WAN related issues along with QoS issues on various interfaces. Sarala has been with Cisco for 11 years and has worked as a software engineer in the Network Software and Systems Technology Group. She holds a master's degree in computer engineering from Santa Clara University and a master's degree in mathematics from Osmania University, India. She also holds CCIE certification (#29921) in Routing and Switching.

Remember to use the rating system to let Sarala know if you have received an adequate response.

Sarala might not be able to answer each question due to the volume expected during this event. Remember that you can continue the conversation on the Network Infrastructure WAN, Routing and Switching discussion forum shortly after the event. This event lasts through January 13, 2012. Visit this forum often to view responses to your questions and the questions of other community members.

Michael Marzol · ‎01-12-2012

Hello Sakella,

That worked perfectly. I may need to tweak the CIR / mincir a bit, but packets are being marked and treated properly.

Thanks!

ymcacisco · ‎01-11-2012

I like so many people have been trying to figure out why my QOS policy doesn't give priority to voice. I have an 1841 router and below is my policy map:

When I look at Strict Priority I have 0\0.

<<< Here is my policy and class map>>>

class-map match-any voice
match access-group 105
match ip dscp ef
!
!
policy-map test
class voice
priority 500
class class-default
policy-map QOS
class class-default
shape average 50000000
service-policy test

<<< policy applied to interface>>>>>

interface FastEthernet0/0.80
encapsulation dot1Q 80
ip address 10.2.17.2 255.255.255.0
ip nat outside
ip virtual-reassembly
no snmp trap link-status
service-policy output QOS

<<>>>

Service-policy output: QOS

Class-map: class-default (match-any)
    266957331 packets, 64135687944 bytes
    5 minute offered rate 3000 bps, drop rate 0 bps
    Match: any
    Traffic Shaping
         Target/Average   Byte   Sustain   Excess    Interval Increment
           Rate           Limit bits/int bits/int (ms)      (bytes)
       50000000/50000000 312500 1250000   1250000   25        156250

      Adapt Queue     Packets   Bytes     Packets   Bytes     Shaping
      Active Depth                         Delayed   Delayed   Active
      -      0         266957344 4006146670 0         0         no

Service-policy : test

      Class-map: voice (match-any)
        49575139 packets, 10644477652 bytes
        5 minute offered rate 0 bps, drop rate 0 bps
        Match: access-group 105
          49546103 packets, 10638278904 bytes
          5 minute rate 0 bps
        Match: ip dscp ef (46)
          29035 packets, 6198530 bytes
          5 minute rate 0 bps
        Queueing
          Strict Priority
          Output Queue: Conversation 264
          Bandwidth 500 (kbps) Burst 12500 (Bytes)
         (pkts matched/bytes matched) 0/0

(total drops/bytes drops) 0/0

      Class-map: class-default (match-any)
        217382198 packets, 53491210234 bytes
        5 minute offered rate 3000 bps, drop rate 0 bps
        Match: any

sakella · ‎01-13-2012

Class-map: voice (match-any)
        49575139 packets, 10644477652 bytes
         5 minute offered rate 0 bps, drop rate 0 bps
         Match: access-group 105
         49546103 packets, 10638278904 bytes
           5 minute rate 0 bps
         Match: ip dscp ef (46)
           29035 packets, 6198530 bytes
           5 minute rate 0 bps
         Queueing
           Strict Priority
           Output Queue: Conversation 264
           Bandwidth 500 (kbps) Burst 12500 (Bytes)
        (pkts matched/bytes matched) 0/0   <<<<<<<<<<<<-show matches only during congestions which when packets get queued

We two packet counters in a class

•1) Packets

Which means the number of packets which match the criteria of the class. This counter increments whether or not the interface is congested.

•2) (pkts matched/bytes matched) 0/0

Which mean the number of packets which match the criteria of the class when the interface was congested. In other words, the interface transmit ring was full, and the driver and the L3 processor system worked together to queue the excess packets in the L3 queues, where the service policy applies. Packets that are process-switched always go through the L3 queuing system and thus increment the "packets matched" counter.

At the time this output was taken there is no congestion as the offered rate was 0 , and hence

(pkts matched/bytes matched) 0/0 is expected .as this counter will only increment for processes switched packets or when there is congestion .

Here is a good link for reference

http://www.cisco.com/en/US/tech/tk543/tk760/technologies_tech_note09186a0080108e2d.shtml

desmond.s · ‎01-12-2012

Hello Sarala,

I have two sites:

Site A 2 T1(3Mbps) Site B

2911----------------------------------------------------------2911

Multilink Multilink

Data Vlan Data Vlan

MGMT Vlan MGMT Vlan

I want to ensure that the data vlan always has the highest priority sending traffic from A to B and B to A, how can I accomplish this?

Thank you!

sakella · ‎01-13-2012

Create a class-map to match Data Vlan Traffic

class-map

match vlan

<<">>

Now create policy-map to mark the traffic

policy-map

class

...mark the traffic as needed

Now Apply the policy on the interfaces connected to 2911

interface

service-policy output

Verify:

You can look at the output "show policy-map interface "

Example:

class-map class-vlan

match vlan 100

policy-map policy-vlan

class class-vlan

<>

interface gi1/1

service-policy output policy-vlan

Support Restrictions to match vlan:

The following restrictions apply to the match vlan command:

•The match vlan command is supported for IEEE 802.1q and Inter-Switch Link (ISL) VLAN encapsulations only.

•As of Cisco IOS Release 12.2(31)SB2, the match vlan command is supported on Cisco 10000 series routers only.

Here is the link:

http://www.cisco.com/en/US/docs/ios/qos/command/reference/qos_m1.html#wp1038903

Another useful link:

http://www.cisco.com/en/US/docs/ios/qos/configuration/guide/qos_on_lac_ps6350_TSD_Products_Configuration_Guide_Chapter.html

Cisco-Spider · ‎01-12-2012

I have a question.

I have an agreement with my ISP for 100mb dedicated bandwidth. Can I test it using any QOS method ?

sakella · ‎01-13-2012

For testing purpose you can have policer for 100 MB which will controll the traffic so that it would not go beyond 100 MB

here is the sample configuration

policy-map LIMIT

class class-default

police 100000000

interface XXX

service-policy out LIMIT

show policy-map int XXX should show the drops if packets go above 100 MBPS.

if you have a QoS policy already then you will be needing to configure 2 level parent-child policy