SNMP Simple Network Management Protocol a set of operations that allow us to monitor our networking devices like routers switches servers printers and what ever else you can put in your network. we have today basicly 3 versions of SNMP SNMP Version 1 defined in RFC 1157 SNMPv1 security is based on communities, that are plain-text strings that allow any SNMP-based application that knows the strings to gain access to a device's management information. also there are 3 types of communities read only - you can read information from the agent read write - you can both read and modify information on the agent trap - sent by the agent according to the policy. SNMP Version 2 defined in RFC 3416, RFC 3417, and RFC 3418 called also community-string-based SNMPv2. SNMP Version 3 latest and gratest define standard: RFC 3410, RFC 3411, RFC 3412, RFC 3413, RFC 3414, RFC 3415, RFC 3416, RFC 3417, RFC 3418, and RFC 2576. this is actually the same as SNMPv2 but with Security enhacments, meaning Authentication MD5, or Message Digest 5 with digest 128 bit, and SHA1, or Secure Hash Algorithm 1 with digest 160 bit. Encryption of SNMP data itself also by using privecy with CBC-DES algorithm. SNMP use UDP port 161 for sending and receiving requests (read - write) and 162 for receiving traps from agents. the structure of the SNMP is like a tree where you have OID (object identifier) that are represented by series of integers separated with dots. here is a simle SNMP config ShiranA(config)# snmp-server community shiranrw RW ;(default is private) ShiranA(config)# snmp-server community shiranr RO ;(default is public) ShiranA(config)# snmp-server location my home address ShiranA(config)# snmp-server contact Shiran Guez ShiranA(config)# snmp-server host 192.168.1.1 shiranr ;this is the destinations that the traps will be sent This is a basic config that sets SNMP enable with both read and write communities and trap server destination.
I know this is very brief article but i think it summarizes SNMP best for understanding and also you have good links to the RFC and more information for filling up the gap.