Installing and configuring SSH on Linux

Posted on 2000-02-29
Last Modified: 2010-03-18
Does anybody know how to install and configure SSH and be able to enable it through the firewall(Linux running ipchains)?

Question by:samcumar
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Expert Comment

ID: 2572813
Sure, somebody knows. But you should explain what exactly you want to do. And at what point you have stopped.

Questions for you for start:
1) do you want to install ssh on firewall machine or on one behind it;
2) where do you need to connect using ssh (select all that apply):
  a) to firewall from inside;
  b) to firewall from outside;
  c) to internal from outside;
  d) from inside mashine to outside server;
  e) from firewall to outside server;
  f) from firewall to inside server.
3) what version of Linux you are running;
4) are you ready to use ./configure;make;make install or you want to get everything precompiled?

Expert Comment

ID: 2573579
I guess, as long as you do ACCEPT TCP port 22, the default port for SSH.

Author Comment

ID: 2574634
These are the Answers to your question:-

1) I want to install ssh on my firewall and also on my webserver

2) The options that I choose are (b), (c) & (f)

3) (i) The firewall is running RedHat 5.2 but I upgraded the kernel to 2.2.12.
(ii) The webserver is running redhat 5.2 kernel ver 2.0.36 but I will be upgrading it to redhat 6.2 very soon.

(4) This is where I'm confused at the moment and I couldn't understand fully the README file for SSH.
What do I need to do here?

Thanks in advance for your help.

Expert Comment

ID: 2575476
Are you just asking how to ssh to a machine behind the firewall?

Accepted Solution

monas earned 100 total points
ID: 2575488
OK, question #5 is what version of ssh you trying to install.

Assuming  you installing 1.2.27 - then installation instructions are not in file README, but in file INSTALL. At the very begining of the file are three lines:

make install

these are the commands you need to invoke (all of them will require some time to complete and produce lot of output). Yes - there are lots of options for configure, but default set produces secure and reasonable configuration. Go with default. And if you will want to change something - you will be able rerun from the very begining.

When make install will complete - you will have software installed. To check that, you need to start ssh daemon (sshd), and then invoke "ssh localhost". [If] you succeed - you will arange sshd to start on every reboot of computer authomagically.

Do all this on internal server. When you are done with local installation you will be ready for enabling option (f). Assuming you have working configuration for your web connections from outside on your firewall check out /etc/ipchains.rules. There should be lines with 80:80 in them - double those and substitute 80:80 with 22:22 - as jyu_88 said - ssh works on port 22, and this way you will allow connections to it. Then run "/usr/bin/ipchains-restore < /etc/ipchains.rules"

When you'll find this working - add rules on firewall to
b) accept connections from everythere to port 22 on firewall;
d) if you don't do masquerading from internal network for all protocols - you should add rule to masquerade 22 port from your internal server to outside

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Author Comment

ID: 2578587
Thanks Monas,

The version of ssh I downloaded is 2.0.13. So I have to look at the README file then.

I shall try out on this Saturday. I will let you know if it works or not.

Thanks for your help.

Expert Comment

ID: 2578721
SSH2 with protocol 2.0 version above has license problem if you donot limit it to personal/home use. For free one, you have to stick to SSH1 with protocol version 1.50 and package version 1.2.27 (then you need to compile with RSAref instead of RSA, also you need to patch RSAref and ssh according to CERT warning)

Author Comment

ID: 2578854
Thanks for the update.
LVL 40

Expert Comment

ID: 2583260
You might also take a look at the new Universal SSH ( I know that it is/will be free for educational institutes and the current beta if free for all use.

Author Comment

ID: 2610549
Thanks for the answer Monas, it worked. Though I struggled it finally worked.

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