snmpd binds to 127.0.0.1 by default

[Tim Ehlers]

This seems to be a major issue for people trying to setup snmpd in ubuntu. There are hundreds of post in forums and blogs of users confused about this. Many post have users editing and re-editing their snmpd.conf files and dont even realize the daemon is bound to 127.0.0.1 from the default config. Why is this setup to bind to 127.0.0.1 by default?

"
The net-snmp FAQ says "Normally, the agent will bind to the specified port on all interfaces
  on the system, and accept requests received from any of them."

http://net-snmp.sourceforge.net/docs/FAQ.html#How_can_I_listen_on_just_one_particular_interface_

However I see that on my Feisty system the /etc/init.d/snmpd startup script bound snmpd to only the localhost interface:

$ ps -ef|grep snmp
snmp 6591 1 0 04:11 ? 00:00:00 /usr/sbin/snmpd -Lsd -Lf /dev/null -u snmp -I -smux -p /var/run/snmpd.pid 127.0.0.1

$ netstat -natup|grep 161
udp 0 0 127.0.0.1:161 0.0.0.0:*

I can manually launch snmpd without the 127.0.0.1 parameter and then it will not bind to any specific interface:

$ sudo netstat -natup|grep snmpd
udp 0 0 0.0.0.0:161 0.0.0.0:* 7178/snmpd
"