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Recipe 17.15 Setting SNMP Packet Size

17.15.1 Problem

You want to change the default SNMP packet size.

17.15.2 Solution

The following configuration command adjusts the default packet size for all SNMP packets leaving the router:

Router#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#snmp-server packetsize 1480
Router(config)#end
Router#

17.15.3 Discussion

By default, Cisco routers limit their SNMP packet size to 1500 bytes. It is usually not necessary to change this parameter. However, it may be useful to reduce it if your network has an MTU of less than 1500 bytes, to prevent unnecessary fragmentation. The conventional wisdom on UDP packets is that smaller is usually better than larger because of fragmentation.

Conversely, if your network media can accepts a larger MTU than 1500 bytes, increasing your SNMP packet size can improve performance, particularly when transferring large MIB tables.

Note that adjusting the maximum SNMP packet size will affect all types of SNMP packets, including responses to SNMP get or set requests, as well as SNMP traps and SNMP informs. You can set the SNMP packet size to any integer between 484 and 17,940 bytes.


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