Confira a man page para snmpd.conf -
agentaddress [<transport-specifier>:]<transport-address>[,...]
defines a list of listening addresses, on which to receive incoming
SNMP requests. See the section LISTENING ADDRESSES in the
snmpd(8) manual page for more information about the format of listening address
Então, tente adicionar algo assim ao topo do snmpd.conf:
Ouça as conexões em todas as interfaces (IPv4 e IPv6)
agentAddress udp: 161, udp6: [:: 1]: 161