Mongodb not listening on all interface Infrastructure : I have 3 virtual machines ip in a DMZ on a same lan.
one of them is running mongodb . OS : RHEL 

Mongod.conf : I have commented out the bindIP option

But still mongodb is not accpeting connection from other servers on LAN. Telnet is failing from other 2 servers

the netstat output is 

Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 0.0.0.0:27017           0.0.0.0:*               LISTEN      24251/./mongod
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      1508/sshd
tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN      1621/master
tcp6       0      0 :::22                   :::*                    LISTEN      1508/sshd
tcp6       0      0 ::1:25                  :::*                    LISTEN      1621/master


i m guessing the foreign address for 27017 port should also look like ":::*" 
I m not able to catch the problem here.Please help!
If you have firewall running, allow connections on port 27017, MongoDB default port.

Not sure which RHEL version you are running so below commands might change. 

1. Any connections can connect to MongoDB on port 27017

iptables -A INPUT -p tcp --dport 27017 -j ACCEPT


2. Only certain IP can connect to MongoDB on port 27017

iptables -A INPUT -s &lt;ip-address&gt; -p tcp --destination-port 27017 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -d &lt;ip-address&gt; -p tcp --source-port 27017 -m state --state ESTABLISHED -j ACCEPT


For Eg:

    iptables -A INPUT -s 192.168.6.100 -p tcp --destination-port 27017 -m state --state NEW,ESTABLISHED -j ACCEPT
    iptables -A OUTPUT -d 192.168.6.101 -p tcp --source-port 27017 -m state --state ESTABLISHED -j ACCEPT


Also i personally believe commenting bind option is not a good idea.

Instead you can use below in /etc/Mongod.conf :

# Listen to local and LAN interfaces.
bind_ip = 127.0.0.1,x.x.x.x, x.x.x.x


and then 

service mongod restart