ModSnmp Manual v3.14 - 4.1.3. Socket settings
The following items must be configured for a socket (TCP or UDP) interface:
Host. The host name or IP address of the device(s) (or Modbus bridge/gateway).
Port. The port number that ModSnmp should connect to on the device (or Modbus bridge/gateway).
Local host. You would normally leave this field empty. However, if you are using a computer that has multiple network interfaces, you can enter the host name or IP address of one of the network interfaces to force that interface to be used for the connection to the device.
Local port. You would normally leave this field set to 0, which allows dynamic allocation of the local port to be used for the connection. However, some firewalls or NAT (Network Address Translation) systems may require you to set a specific port.
The same host and port may be used in more than one interface. If this is done, ModSnmp will open a separate socket connection for each interface. This can be useful if you have more than one device on the same host and port, and want to access the devices concurrently.