You want to change the default SNMP packet size.
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#
By default, Cisco routers limit their SNMP packet size to 1,500 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 1,500 bytes to prevent unnecessary fragmentation.
Conversely, if your network media can accepts a larger MTU than 1,500 bytes, then 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 8,192 bytes.