Re: Puzzling QoS Issue

Another interesting fact - When the policy is applied as shown above, the
problem only occurs when the inbound RX is congested.

So basically, if the service-policy is applied outbound towards the WAN as
shown, and the output utilization of the WAN link (TX) is low, and the
inbound (RX) utilization is low, everything is fine.

In the event that the inbound utilization of the interface (RX) is
significant, and the policy is applied outbound as usual, the policy is
adding the 200-400ms extra delay. If I remove the policy, the extra delay
goes away.

I guess I don't understand why inbound congestion would change how the
outbound queue / shaping works.

input is low, output is low, policy applied: fine
input is high, output is low, policy not applied: expected poor response
times
input is high, output is low, policy is applied: expected poor response
time PLUS an additional 200-400ms of delay

On Fri, Apr 19, 2013 at 5:49 PM, Joe Astorino <joeastorino1982_at_gmail.com>wrote:

> I have a 3945 ISR router connected via a GigabitEthernet link to a service
> provider that is providing 10Mbps WAN access. I wish to use CBWFQ and the
> service provider requires dot1q tagging. As such, I must shape my
> sub-interface and use a hierarchical type QoS policy...no big deal
>
> policy-map WAN-EDGE
> class VOICE
> priority percent 20
> !
> class VIDEO
> bandwidth remaining percent 60
> queue-limit 128 packets
> !
> class APPS_SIGNALING
> set dscp af21
> bandwidth remaining percent 30
> !
> class class-default
> bandwidth remaining percent 10
> !
> !
> policy-map SHAPE-OUT
> class class-default
> shape average 10000000
> service-policy WAN-EDGE
> !
> !
> int gi0/1.2
> encapsulation dot1q 2
> ip address ...
> service-policy output SHAPE-OUT
>
>
> Here is the very strange thing. Even when the TX of this WAN interface is
> barely being used, when and only when the service-policy is applied, the
> response in pings to anything behind this router increase immediately by
> 200-400ms. Immediately after removing the service-policy things return to
> normal.
>
> Investigating the output of "show policy-map interface" reveals a large
> number of output drops in the shaper class-default. So far I have tried
>
> - increasing the queue-limit to many different combinations
> - increasing the burst size
>
> I also have the exact same configuration on another remote site router
> running the same version of IOS with the same setup (10Mbps Ethernet WAN
> link) on the same platform.
>
> I'm really baffled as to what would cause this. Any insight appreciated.
>
>
>
> --
> Regards,
>
> Joe Astorino
> CCIE #24347
> http://astorinonetworks.com
>
> "He not busy being born is busy dying" - Dylan
>

-- 
Regards,
Joe Astorino
CCIE #24347
http://astorinonetworks.com
"He not busy being born is busy dying" - Dylan
Blogs and organic groups at http://www.ccie.net