Hello David
The snmp-server community text ro/rw command is indeed all that’s necessary to allow an SNMP manager to retrieve information from the network device or agent, and also to set specific configuration parameters. The ability to retrieve and set depends of course on the ro (read only) or rw (read/write) setting in the command.
The snmp-server host x.x.x.x command serves a different purpose. This command tells the SNMP agent where to send unsolicited messages, specifically traps and informs. Unsolicited messages are those messages sent by an SNMP agent to an SNMP manager without the manager first requesting that information. These messages are used to alert the manager about specific events or conditions that have occurred in the agent device.
If the snmp-server host command is not issued, no unsolicited messages are sent. But as long as the snmp-server community command is set, SNMP information can be retrieved by the SNMP monitor.
According to the Cisco command reference links below, the default value for the SNMP version found within the snmp-server host command is version 1, however, this may depend upon the platform and IOS versions. Using the context-sensitive help in the CLI may inform you of the default value for this on your platform.
The version number specified in this command has to do with the types of traps and informs that will be used. Specifically:
- SNMP version 1 doesn’t use informs, and has a particular format for traps.
- SNMP version 2 introduces informs and changes the format of traps
- SNMP version 3 doesn’t change the format of these messages, but adds security features like authentication and encryption.
What version you configure will change these formats and parameters such that the receiving SNMP server will receive the appropriate types of messages.
So the question is, if you use version 2c on the command, is this backward compatible with an SNMP manager that understands version 1 formats? I haven’t found any documentation making this claim. When you say that “the SNMP server can still communicate with the managed device using v1,” can you clarify what you mean?
Take a look at these Cisco command references for these commands for more info:
I hope this has been helpful!
Laz