To avoid the performance problems that can occur when SNMP is used to retrieve the routing table or the ARP table, configure the router as described in either of the following sections: Therefore, any CPU spikes that might occur during SNMP route polling should not affect router performance. This means that the CPU processes non-SNMP requests before it processes SNMP requests. To the CPU scheduler, SNMP is a low-priority process. Therefore, even if your router does not currently exhibit CPU spikes, it might begin to do so as the size of the routing table increases. Note The number of CPU cycles needed to respond to a request for the entire routing table depends on the size of the table (more routes require more CPU cycles). As the size of the routing table increases, the router must take a proportionately longer time, along with higher CPU processing levels, to sort the table entries.

This means that for each SNMP request for routing information, the router must sort entries into the OID order before it builds the response protocol data unit (PDU). However, RFC 1213 requires that SNMP return the routes in lexicographical order, which means they are listed by their OIDs, in the order in which they occur in the OID tree. The router stores the routing table in hash format, which allows the router to quickly and efficiently search the table.

This allows the management station to learn the topology of the entire network. The management station uses this routing information to find other routers and query them about the networks around them. This section provides background information about the issue and how to avoid the problem.Īn SNMP network management station can query a router to learn about other networks. Using SNMP to poll large routing tables and Address Resolution Protocol (ARP) tables can cause performance problems on the Cisco routers. Remember SNMP is low priority on a routers CPU stack, so in theory you will start to drop the SNMP packets and request not traffic.Ĭisco CMTS Universal Broadband Router Series MIB Specifications Guide 12.2SC - Chapter 2, Configuring SNMP and MIB Support - Cisco Systems High CPU Usage When Polling Routing ARP Tables Here is some stuff you can do or look at. Even more so on a Core router that will be doing BGP and have larger routing tables, and large ARP tables in Enterprise LANs.

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