How to: Allow telnet and ssh through iptables under Linux

by on November 1, 2007 · 5 comments· LAST UPDATED November 1, 2007

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Q. I run both RHEL / CentOS Linux server and by default firewall blocked out everything including telnet / ssh access. How do I allow telnet - port 23 and ssh port 22 thought Linux iptables firewall ?

A.By default firewall rules stored at /etc/sysconfig/iptables location / file under CentOS / RHEL. All you have to do is modify this file to add rules to open port 22 or 23.

Login as the root user.

Open /etc/sysconfig/iptables file, enter:
# vi /etc/sysconfig/iptables
Find line that read as follows:
COMMIT
To open port 22 (ssh), enter (before COMMIT line):

-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT

To open port 23 (telnet), enter (before COMMIT line):

-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 23 -j ACCEPT

Save and close the file. Restart the firewall:
# /etc/init.d/iptables restart

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{ 5 comments… read them below or add one }

1 X-Modius November 27, 2007 at 8:55 pm

To get fancy with iptables and block repeated failed connection attempts, check out this article:

http://www.itwire.com/content/view/13841/53

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2 Shiva May 24, 2008 at 7:42 am

send me code of linux firewall in C.

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3 nixCraft May 24, 2008 at 3:48 pm
4 Liju June 1, 2008 at 4:15 pm

Hi,

I don’t think this is not a good idea to allow telnet access nowaday.nobody is using telnet on linux box. Disable this service first

Also it is not a good idea to allow ssh access to everyone over the net
# Permitt SSH access to my ip and my network
/sbin/iptables -A INPUT -s 8.23.2.11 -p tcp –dport ssh -j ACCEPT
/sbin/iptables -A INPUT -s 4.3.8.0/24 -p tcp –dport ssh -j ACCEPT

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5 V.Balaviswanathan June 18, 2009 at 9:11 am

Thanks for the info, How do I use iptables in squid to block messanger or chat tools? Could any one help me please

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