I have Cacti installed so that I have pretty graphs (CPU/load/memory/disk/network) for all my servers (VPS) in one place. I just enabled full IPv6 on one of them and Cacti stopped working. The problem wasn’t Cacti though, it was the server it was now trying to contact through IPv6.

As I only need SNMP for Cacti, the snmpd.conf file on all my servers is very simple, just:

rocommunity public

However for IPv6 that isn’t enough. On Ubuntu 14.04 (what the server is running) snmpd will only work on IPv4 this way. I quickly found out you can use an agentAddress directive in the snmpd.conf file to enable the daemon to listen on IPv6, but more changes are required if you want to actually return data through IPv6. As it turns out the “rocommunity” directive is apparently also IPv4 only.

The final solution was this:

agentAddress udp:161,udp6:161
rocommunity public
rocommunity6 public

Warning: above configuration will cause snmpd to listen on all network interfaces. Be sure to lock down access to UDP port 161 in your firewall to only authorized hosts. And make sure your firewall supports IPv6.