tx-ring-limit Analysis

souagarw · ‎03-04-2009

Hi,

As per my understanding with tx-ring value is that it is dependent on bandwidth configured on the interface and not to the specific platform nor to the IOS. Please correct if I'm wrong.

Also, can anyone point me to the URL where I can get the default value of tx-ring and its range for different interfaces and fixed systems.

Can there be any situations where tx-ring value can't be configured for interfaces?

Is there any best practice or any guidelines which should be kept in mind while tweaking tx-ring values?

Appreciate your help.

Regards

Sourabh

Joseph W. Doherty · ‎03-04-2009

"Can there be any situations where tx-ring value can't be configured for interfaces? "

Not 100% positive, but the very latest IOS versions might reject the tx-ring command.

"Is there any best practice or any guidelines which should be kept in mind while tweaking tx-ring values? "

When working with real-time traffic, that's software queued with something like LLQ, you often need to tune the value down.

Mohamed Sobair · ‎03-04-2009

Hi,

As you know the router has 2 type of Queues:

The Hardware Queue which is always FIFO, and the Software Queue determined by any Queuing Strategy to hold the packet.

Tx-ring limit defines the number of packet stored on the Hardward Queue before leaves a router.

Its highly recommended on high Speed links to modify the tx-ring limit to the lower value possible in order to improve the performance and minimizes drops.

Have a look at the bellow document:

http://www.cisco.com/application/pdf/paws/6142/txringlimit_6142.pdf

HTH

Mohamed

souagarw · ‎03-13-2009

Thanks for the URL. However still have below questions.

1. I got to know that most of the software based IOS platforms running 12.3 or later code should automatically adjust the tx-ring when the service-policy is applied to the interface. Is this true? Can you share any URL with the specifications to support this?

2. Also are there any general guidelines through which tx-ring value can be recommended or it requires testing before?

3. How to determine tx-value for fixed chassis, for interface, it can be determined by show controllers?

Regards

Sourabh