Auto Tuning Buffers

Problem

You want the router to automatically tune the buffers, based on computed needs of the router.

Solution

Use the buffers tune automatic command to enable the router to auto tune the system buffers:

Router#configure terminal 
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#buffers tune automatic 
Router(config)#end  
Router#

This command was introduce in IOS Version 12.3(14)T, and the router computes the correct buffer parameters regardless if the command is entered or not. Once the buffers tune automatic command is entered, the router buffers will change to the computed values.

Discussion

As we discussed in Recipe 2.3, tuning the router's system buffers can be a tricky endeavor that can result in poor performance if not done correctly. What's more, Cisco recommends against the practice of tuning system buffers without assistance from their technical support representatives.

With the introduction of auto tuning of system buffers, the end user can enable the feature and allow the router to monitor and calculate the correct system parameters. Because the router continues to monitor the buffer parameters over time, you can be assured the buffer parameters will remain properly set, which means there's no need to revisit the settings.

As we mentioned in the Solution section, the router automatically begins calculating the correct buffer parameters based on system requirements, even if the feature isn't immediately enabled. Once enabled, the router will use the computed parameters.

To monitor the parameter changes to the system buffers, use the show buffers tune command:

Router# show buffers tune 

Tuning happened for the pool Small
Tuning happened at 22:43:19
Oldvalues
permanent:50 minfree:20 maxfree:150
Newvalues
permanent:62 minfree:15 maxfree:78
Tuning happened for the pool Middle
Tuning happened at 22:43:19
Oldvalues
permanent:25 minfree:10 maxfree:150
Newvalues
permanent:36 minfree:9 maxfree:45
Router#

This example shows that the router automatically tuned the buffer settings at 22:43. It also shows that the router adjusted the Small and Middle buffers, and includes the old and new values.

The autotuning feature will override the manually set values if necessary. Be sure to remove all manual buffer change statements before enabling the auto tuning feature.

 

See Also

Recipe 2.3.