This should be extremely easy to setup given that I had done this before a few times already.

We are setting up Cacti in the Amazon EC2 cloud to monitor the environment and I'm setting up SNMP on the Linux hosts.
I'm not able to do a snmpwalk from hosts on the same subnet. snmpwalk works locally though. (snmpwalk -v2c public localhost) The snmpd.conf is a new install and out of the box without modification and so the community name is public for testing.
Tested without firewall but no luck.
Ran tcpdump to listen traffic between two hosts. None.
Ran tcpdump to listen traffic between two hosts with nc and I'm able to access the ports! (So firewall/routes is not the issue, I believe)
SELinux is running but nothing is logged on audit.log. Just to make sure, I ran it in permissive mode but no luck there either.
Again to test, I put a "rocommunity public" on the snmpd.conf file and did a service restart. No luck again.
Can someone help?

161 TCP/UDP open in Security Groups?

Thank you for replying.
It looks like traffic was allowed for TCP ports only. Silly me.

Thank you again.

Glad it worked out.