Oh the joys of overcoming poor software design! You'd have thought that an application like snmpd, which allows you to configure who can access the SNMP information on a server and from which ip-addresses, could be configured as such. Not a bit. That'd be too easy. The default Ubuntu installation screws it up very nicely by launching the snmp daemon with an argument '127.0.0.1' i.e. localhost, which secretly overrides whatever you specify in the snmpd.conf file. You can only access from localhost, even if you used snmpconf to specify access for all. To fix the problem you have to edit the /etc/default/snmpd file and delete the '127.0.0.1' from the end of the line that starts with 'SNMPDOPTS'. Then it works.