log into the Xenserver via SSH, or get a console through XenCenter.

Open up the snmpd.conf file with your favorite text editor, nano, vi etc.

vi /etc/snmp/snmpd.conf

Find the line the following line

com2sec notConfigUser default public

and change the source “default” to the allowed IP ranges and the community “public” to whatever you want your new community string to be.

Example:

com2sec notConfigUser 192.168.1.0/24 privateString

Save, exit and start snmpd

service snmpd start

Add the following line in your iptables config.  It needs to be above the COMMIT line.

-A RH-Firewall-1-INPUT -s 0.0.0.0/0 -m udp -p udp --dport 161 -j ACCEPT

Restart iptables

service iptables restart

You should be good to go.