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I'm trying to link my new laptop running 11.10 to my old laptop running 8.04 through my router using SSH.

This question is asked and answered on ubuntuforums here:

http://ubuntuforums.org/showthread.php?t=1648965

I thought it would be helpful to have a more definitive answer here.

Note: I needed to first install openssh-server on the laptop I was trying to connect to and open up the SSH port in my firewall using firestarter.

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can you please tell us what is not "definitive" enough about slooow's answer on that thread? Otherwise your question seems to ambiguous. –  d_inevitable Mar 25 '12 at 18:25
    
@d_inevitable For one, it's not the only answer and it's not otherwise indicated as the correct one. It's the one I would have chosen, but this is why I thought it'd be useful to migrate this question. It might also help to include general directions, or a helpful link, on configuring SSH between two local machines. –  klenwell Mar 25 '12 at 18:43
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2 Answers 2

up vote 13 down vote accepted

You can restrict access to your ssh server in many ways.

IMO the most important is to use ssh keys and disable password authentication.

See the following wiki pages for details

https://help.ubuntu.com/community/SSH/OpenSSH/Keys

https://help.ubuntu.com/community/SSH/OpenSSH/Configuring#Disable_Password_Authentication

You can restrict access to a specific subnet in several ways. I will assume your ssh server is on subnet 192.168.0.0/16 with an ip address of 192.168.0.10 , adjust accordingly ;)

Router

One line of defense is to use a router. Be sure to disable UPnP and do not allow port forwarding.

SSH configuration

You can set several options in /etc/ssh/sshd_config. One is the listen address. If You set a listen address on your subnet. A private ip address is not routable over the internet.

http://compnetworking.about.com/od/workingwithipaddresses/f/privateipaddr.htm

ListenAddress 192.168.0.10

You can also use the AllowUsers

AllowUsers you@192.168.0.0/16

Somewhat related, you can also change the port

Port 1234

See http://manpages.ubuntu.com/manpages/precise/man5/sshd_config.5.html

TCP wrapper

As outlined on the forums post, you can use TCP Wrapper . TCP wrapper uses 2 files, /etc/hosts.allow and /etc/hosts.deny

Edit /etc/hosts.allow and add your subnet

sshd : 192.168.0.

Edit /etc/hosts.deny , and deny all

ALL : ALL

See also http://ubuntu-tutorials.com/2007/09/02/network-security-with-tcpwrappers-hostsallow-and-hostsdeny/

Firewall

Last you can firewall your server. You can use iptables, ufw, or gufw.

iptables

sudo iptables -I INPUT -p tcp --dport 22 -s 192.168.0.0/16 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 22 -j REJECT

Please do not use DROP in iptables, see http://www.chiark.greenend.org.uk/~peterb/network/drop-vs-reject

ufw

sudo ufw allow from 192.168.0.0/16 to any port 22

gufw has a graphical interface

GUFW

See https://help.ubuntu.com/community/UFW

https://help.ubuntu.com/community/IptablesHowTo

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Some networks use 10.0.0.0 as IP address, in that case substitute 192.168.0.0/24 for 10.0.0.0/8 to allow for the range 10.0.0.0-10.255.255.255. If you want to allow a single IP only, use something like 192.168.1.2/32. A very verbose explanation can be found on [serverfault.com/q/49765/51929](How does Subnetting Work?) –  Lekensteyn Apr 1 '12 at 8:32
    
Please do not use DROP in iptables - See chiark.greenend.org.uk/~peterb/network/drop-vs-reject –  bodhi.zazen Mar 3 at 16:46
    
That page does not mention spoofed IPs as a possible reason to use DROP over REJECT. This answer on Sec.SE explains why it is not really relevant though (the source packets are larger than the returned packets). –  Lekensteyn Mar 3 at 17:35
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ssh(secure shell) is used to access and transfer data securely(used RSA_KEYS pair). You can access data using ssh in two ways 1. Command line 2. using file browser

Command Line: For this you don't need to install anything. First task is log-in into other computer.

ssh other_computer_username@other_computer_ip

This command will ask for a password which is the other computer's password(for specific user-name). You have just logged in to other computer's shell. Think this terminal is like your computer shell terminal. You can do everything using shell to other computer that can you do in your computer

File browser: You need to install openssh-server

sudo apt-get install openssh-server

To log-in go to file->connectToServer

enter image description here

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Command line directions were the first thing I tried. I was able to ping my other computer at its LAN IP. But when I try to SSH, it hangs. So I assume I have to configure my other computer to allow SSH access first. –  klenwell Mar 25 '12 at 18:51
    
make sure that your router does not block 22 port or ssh –  shantanu Mar 25 '12 at 19:42
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