The Zenoss installation added its own server into the devices list as a default.  However, it is having trouble reading snmp values from itself.  Performing snmpwalk via the Zenoss web interface results in a timeout error.

The snmpwalk command used by Zenoss uses the IPv6 loopback address ::1.  I switched this to the IPv4 equivalent 127.0.0.1 and the snmpwalk worked fine.

It turns out, the snmp agent, net-snmp, only listens to IPv4 addresses by default.  Some changes need to be done to the net-snmp config file.

The following lines need to be added to /etc/snmp/snmpd.conf:

agentaddress udp:161
agentaddress udp6:161

#         sec.name       source          community
com2sec   notConfigUser  default         public
com2sec6  notConfigUser  default         public

Restart snmpd and it should now listen to IPv6 as well.

# service snmpd restart