What is an SNMP community?

Short answer

An SNMP community is the name, shared between the device and the NMS in SNMP v1 and v2c, that functions as a password (RFC 1901); the party that knows the same community name can query the device or recognize the trap. It does not provide encryption and is carried in plain text on the network; therefore it is used only on trusted networks. In TR7, it appears in two places. For sending traps, the SNMP Community Name field in the SNMP Settings section is used; if the field is left empty, public is assumed, and when SNMP Version v3 is selected, the field is hidden. On the agent side, the Community Name is entered when SNMPd V2 is turned on in Management Access; SNMPd V1, on the other hand, grants access with the fixed public community. Both communities of the agent grant only read access.

Where It Is Used in TR7

Where	Field / label	What for
Settings → General Settings → Notification Management → SNMP settings	SNMP Community Name (public if empty; visible while SNMP version is v1 or v2c)	The community of the traps sent
Settings → Device Management → Management Access → Edit → SNMP	SNMPd V2 → Community Name (required)	The community to be used in v2c queries
Same form	SNMPd V1	v1 query access with the fixed public community
Same form	SNMP Allowed Networks	Accepting queries only from these networks, even when the sender knows the community

• An example of querying the agent is given in the info text in the form: snmpwalk -v1 -c public $IP:$PORT for v1, and snmpwalk -v2c -c $COMMUNITY_NAME $IP:$PORT .1 for v2c.

Common Misconceptions

• "The community name provides encryption." The community is only a shared name; the traffic is not encrypted. For authentication and encryption, SNMPd v3 is used on the agent side.
• "If the field is empty, no trap is sent." An SNMP Community Name left empty is assumed to be public.
• "The community of SNMPd v1 can be changed." SNMPd v1 uses the fixed public community; for a custom community, SNMPd v2 is turned on. To prevent unwanted access, SNMP Allowed Networks is narrowed or SNMPd v1 is kept off.

How it is done in the documentation

• Notification Management · SNMP Community Name
• Management Access · SNMPd v1
• Management Access · SNMPd v2

Related questions

• What is the difference between SNMP v1, v2c and v3?
• What is the difference between SNMP Trap and the SNMP agent?
• What is SNMP; for what purposes is it used in TR7?