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QoS on Gigabit WAN interface

Hello Experts,

Need your inputs:

I have a Cisco 3825 runnnit IOS version:

c3825-spservicesk9-mz.124-12c.bin

configured with Gigabit ethernet 0/1 as the WAN interface. The configs are as follows:

class-map match-any Multimedia

match ip dscp ef

class-map match-any Interactive

match ip dscp cs3

match ip dscp af31

match ip dscp af32

match ip dscp af33

class-map match-any MissionCritical

match ip dscp cs4

match ip dscp af41

match ip dscp af42

match ip dscp af43

!

!

policy-map PrimaryQueues

class Multimedia

priority 1024

class MissionCritical

bandwidth 11008

random-detect dscp-based

class Interactive

bandwidth 256

random-detect dscp-based

class class-default

set dscp default

fair-queue

random-detect dscp-based

policy-map PrimaryQOSOUT

class class-default

shape average 16384000

service-policy PrimaryQueues

interface GigabitEthernet0/1

bandwidth 16384

ip address 192.168.93.14 255.255.255.252

ip nbar protocol-discovery

load-interval 30

duplex full

speed 100

media-type rj45

no keepalive

no cdp enable

service-policy output PrimaryQOSOUT

Will the configuration suffice for QoS or since i'm having gigabit ethernet as my WAN interface, I will need to tweak the transmit ring setting to ensure QoS kicks in. I thought the QoS will kick in once the traffic reaches 70% of 16Mb.

Thanks in advance.

3 REPLIES

Re: QoS on Gigabit WAN interface

Hello.

Your configuration looks good and should work. You should not need to change your hardware queue as when you configure the service-policy on the interface the router automatically shortens it. You can check with the command below

R1#show controllers s2/0

……………………………………..

tx_underrun_err=0, tx_soft_underrun_err=0, tx_limited=0(16)

QoS kicks in as soon as the hardware queue is full. At other times with no congestion QoS doesn't do anything as it doesn't need to.

Only other thing I would like to mention is that you haven't given your class-default a bandwidth setting. This means that your class-default won't get the rest of the bandwidth, instead the un-allocated bandwidth will be shared amoungst the other queues. So, one might think that the class-default might get 4MB but you'll find that bandwidth will be shared out so the class-default in times of congestion might only get 1MB.

Simon

Super Bronze

Re: QoS on Gigabit WAN interface

"Only other thing I would like to mention is that you haven't given your class-default a bandwidth setting."

If you refer to the child policy's class-default, it's using FQ for which, on most platforms and most router IOSs, you can't configure bandwidth unless you don't want FQ.

Super Bronze

Re: QoS on Gigabit WAN interface

"Will the configuration suffice for QoS or since i'm having gigabit ethernet as my WAN interface . . ."

Can't say, not enough information.

". . . I will need to tweak the transmit ring setting to ensure QoS kicks in."

You may although don't see any tunning on the gig interface.

"I thought the QoS will kick in once the traffic reaches 70% of 16Mb."

Why do you think that? QoS should kick in when shaper delays packets. When shaper delays packets depends much on Bc and Tc not just bandwidth.

PS:

When working with WAN Ethernet, you might need to set shaper slower than nomimal bandwidth if you need to account for L2 overhead.

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