By default, snmpd listens for incoming SNMP requests on UDP port 161 on all IPv4 addresses. However, it is possible to modify this behavior by specifying one or more listening addresses as arguments to snmpd. A listening address takes the form:
[<transport-specifier>:]<transport-address>
At its simplest, a listening address may consist only of a port number, in which case snmpd listens on that UDP port on all IPv4 interfaces.
Otherwise, the <transport-address> part of the specification is parsed according to the following:
transport-address format
udp (default) | hostname[:port] or IPv4-address[:port] |
tcp | hostname[:port] or IPv4-address[:port] |
unix | pathname |
udp6 or udpv6 or udpipv6 | hostname[:port] or IPv6-address[:port] |
tcp6 or tcpv6 or tcpipv6 | hostname[:port] or IPv6-address[:port] |
Note that <transport-specifier> strings are not case-insensitive so that, for example, "tcp" and "TCP" are equivalent. Here are some examples, along with their interpretation:
127.0.0.1:161
listen on UDP port 161, but only on the loopback interface. This prevents snmpd being queried remotely.
TCP:1161
listen on TCP port 1161 on all IPv4 interfaces.
unix:/tmp/local-agent
listen on the Unix domain socket /tmp/local agent.
/tmp/local-agent
is identical to the previous specification, since the Unix domain is assumed if the first character of the <transport-address> is '/'.
udp6:10161
listen on port 10161 on all IPv6 interfaces.
Note that not all the transport domains listed above will always be available; for instance, hosts with noIPv6 support will not be able to use udp6 transport addresses, and attempts to do so will result in the error "Error opening specified endpoint".