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Recipe 18.2 Setting the Log Size

18.2.1 Problem

You want to change the size of the router's log.

18.2.2 Solution

You can use the optional size attribute with the logging buffered configuration command to change the size of your router's internal log buffer:

Router#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#logging buffered 16000
Router(config)#end 
Router#

Adjusting the size of the router's logging buffer wipes out all of the current contents of the buffer.

18.2.3 Discussion

The typical default size of a router's logging buffer is 4096 bytes (although some high-end routers will default to a higher value). A buffer of this size can hold approximately 50 log messages before overwriting occurs. 50 messages, although better than no logging, is relatively small and most engineers will want increase their buffer size to store more messages. To check the size of your router's logging buffer, use the show buffer command:

Router>show logging
Syslog logging: enabled (0 messages dropped, 0 messages rate-limited, 0 flushes, 0 
overruns)
    Console logging: level debugging, 653 messages logged
    Monitor logging: level debugging, 65 messages logged
    Buffer logging: level debugging, 1 messages logged
    Logging Exception size (4096 bytes)
    Trap logging: level informational, 657 message lines logged
          
Log Buffer (16000 bytes): 
Router>

As you can see, this router's buffer size is currently set to 16,000 bytes (roughly 16KB).

The router will theoretically accept a wide range of buffer sizes ranging from 4,096 bytes (nothing smaller) to an astronomical 2,147,483,647 bytes (about 2GB). Exercise caution when choosing the size of your logging buffer because it comes out of the router's system memory. A good rule is to set your logging buffer to 16KB for smaller routers. Routers with more than 32MB of memory can safely dedicate 32KB, or even 64KB without problems. To be safe, always check the amount of free memory on your router with the show memory command before increasing your buffer size.

You can also combine the keywords in Recipe 18.1 and Recipe 18.2 into a single configuration command:

Router#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#logging buffered 16000 informational 
Router(config)#end
Router#

In this case, we set the buffer size to 16,000 bytes and the severity level to informational with a single configuration command.

18.2.4 See Also

Recipe 18.1; Recipe 18.2


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