Template:FAQ:Agent 22

Normally, the agent will bind to the specified port on all interfaces on the system, and accept request received from any of them. However, if a particular port (or ports) is specified when the agent is first started, then it will only listen for requests on these particular ports:
For example:

                       snmpd 127.0.0.1:161

would listen (on the standard port) on the loopback interface only, and:

                       snmpd 10.0.0.1:6161

would listen on port 6161, on the (internal network) interface with address 10.0.0.1. If you want to listen on both of these interfaces (and no others), provide a list of all the desired addresses:

               snmpd 127.0.0.1:161 10.0.0.1:6161

The AgentX port option ('-x') works in much the same way.