UNIX for Dummies Questions & Answers

Have -
-3 HP Proliant G4P servers - Debian (wheezy)
-3 RaspPI's - Raspian
-Unmanaged switch that all 6 can ssh into each other with via eth0
-Router (w wifi and 5 ports) - on eth1 of the three G4p's of protocol dhcp

Want:
To let the six servers, in my basement run, since the HPs are loud, and get into my 6 server network via a laptop/tablet that's OS independent (Win, Chrome, Linux) via ssh or see the full windowx remote desktop of any of the 6 servers via the comforts of anywhere in my house through only a mere Laptop/tablet with a wifi connection?

Googling of course spins my head (I'm a data science guy not network eng) and I wonder what I need to do.

Openvpn seems to come up on many google searches....what's this about? Wrong approach?

fwiw, this is a home-based-research-lab I'm setting up (Hadoop, R, etc).

All advice, FAQ's, blogs, links to sites with great 101's on this matter are appreciated

Have a great weekend all!

This shouldn't be too hard: Do you want to access the command line on these servers or do you need graphics too?

A commandline access is easily done: install the ssh-server on your servers (if it isn't already there) and simply use "ssh" (the client) from your laptop. If you happen to have no OS but only this patch job from Redmond on your laptop install some ssh client like "putty", which you can download freely from the net. Exchange ssh-keys and you can even set up passwordless logins.

If you need graphics you will need X-Windows. This is a graphical client-server system and you will need sone X-Server on your laptop (easy if it is any kind of Unix/Linux, otherwise a bit more complicated). The rest will be easy too. For a short introduction to X-Windows concepts terminology read this post.

I hope this helps.

bakunin

Thanks for the reply.

I'm trying to setup something like this:



Since the HP's have Internet dhcp on eth1, can a laptop that's configured to dhcp find another device on that same wifi network. The laptop (runs Win/Linux) but only wifi????

I'm stuck here.

I can connect the laptop to the switch and give it a static ethernet IP and then ssh into any of the 6 servers, but when I go wifi w the laptop I am at a loss....

I'd like to ssh into any of the 6 servers wirelessly from the laptop. And if possible get into the 6 servers like that Windows Remote Desktop tool does (ie I want to run startx on all 6 servers and see that GUI off my wirelessly connected laptop)? Sorry for sounding sooo clueless, I know a little re networking, but not much

---------- Post updated at 09:57 PM ---------- Previous update was at 09:04 PM ----------

update, I was able to connect the laptop to the three HP servers by finding out what their IP was, that the router assigned them using:

Code:

/sbin/ifconfig

woohoo. 1 down, 1 left to go.

Thinking Remmina might work?
http://remmina.sourceforge.net/links.shtml

There are a couple of issues and i am not sure if i manage to answer them all right now (RL demanding my attention), so stay tuned for more tomorrow:

1. Your network setup

Please refrain from posting photos, they are using an awful lot of bandwidth. I have redrawn your picture using ASCII graphics using vi:

Code:

  Switch                 WLAN-Router
    ---                    ---
     |  +--------------+    |
     |--| ProLiant 1   |----|
     |  +--------------+    |
     |  +--------------+    |
     |--| ProLiant 2   |----|            +--------------+
     |  +--------------+    |------------| Laptop       |
     |  +--------------+    |            +--------------+
     |--| ProLiant 3   |----|
     |  +--------------+    |
     |  +--------------+   ---
     |--| Rasberry 1   |    
     |  +--------------+    
     |  +--------------+    
     |--| Rasberry 2   |    
     |  +--------------+    
     |  +--------------+
     |--| Rasberry 3   |
     |  +--------------+
    ---

You have two separate ethernets: one which connects all the servers and one which connects all the ProLiants with the Laptop. While this is possible, it is not desirable at all for your cause.

Such a setup, with a separate "admin LAN" to access the systems is sometimes used in very big installations (data centers) to make it easier to create firewall-rules to limit the physical connection to the admin LAN. You use that to restrict access only to a select number designated client systems, so that even knowing the password would not help a prospective hacker as long as he hasn't access to such a system (the admins workplace) too.

A serious drawback of this setup is that access to the Rasberry systems is only possible via one of the ProLiants, so you will have to enable IP-forwarding on at least one of them or connect the Rasberries to the WLAN router.

In short: this is not a good idea and i think you could make life easier for you. Consider the following:

Code:

                                Switch
                                  ---
                  WLAN-Router      |
                     ---           |  +--------------+
                      |            |--| ProLiant 1   |
                      |------------|  +--------------+
   +--------------+   |            |  +--------------+
   | Laptop       |---|            |--| ProLiant 2   |
   +--------------+   |            |  +--------------+
                     ---           |  +--------------+
                                   |--| ProLiant 3   |
                                   |  +--------------+
                                   |  +--------------+
                                   |--| Rasberry 1   |
                                   |  +--------------+
                                   |  +--------------+
                                   |--| Rasberry 2   |
                                   |  +--------------+
                                   |  +--------------+
                                   |--| Rasberry 3   |
                                   |  +--------------+
                                  ---

This way you need access only to the WLAN-Router to access your whole network and you do not need to activate IP-forwarding (which creates problems all of its own).

You may notice that i haven't made any distinction between WLAN and cable-bound Ethernet: the reason is that there is no difference. For networking a WLAN connection is just "another sort of cable", so to say and above the level of cabling it doesn't matter.

Notice also, that eth1 on the ProLiants is not used any more. You do not need it.

2. DHCP

DHCP (Dynamic Host Configuration Protocol) is a way to assign IP hosts with addresses and was invented to deal with a scarcity of IP addresses. Normally, every IP host will have an address. If you have more and more hosts sharing the same network range IP addresses will eventually become scarce. DHCP was invented, so that this problem could be somewhat alleviated. Not all the systems are permanently active, therefore you do not need as many addresses as you have hosts, but only so many as you have active hosts. One system would do the bookkeeping and give out "leases" with IP addresses when a host starts and collect these addresses when the host shuts down. A host would not be guaranteed to get the same address again if it reconnects.

It is possible to run a network with servers using DHCP if you use some sort of dynamic DNS, so that the IP addresses are dynamic while the DNS names of the servers are static. This is sometimes done (again: in big data centers with hundreds(thousands of servers), but would add a lot of configuration effort to your setup. AND you do not need it at all.

My suggestion is to give static IP addresses to all the servers. Then construct a common /etc/hosts and distribute this among the systems to have name resolution. This is not as elegant as setting up a DNS server, but it is done in seconds instead of hours and the drawbacks for six servers and one client (the laptop) are zero.

You can activate DHCP for your laptop or not, it doesn't matter. If you want to access the Internet at the same time from the laptop you will have to configure it this way:

- use an outside DNS server (to resolve names in the internet)
- put the file "/etc/hosts" with your local systems on it.
- let take "/etc/hosts" take precedence by setting "local, bind4" in "/etc/netsvc.conf"

Now, if you use a name, first the file "/etc/hosts" is queried for it, only then the DNS is asked. Because the DNS would not know about your servers this is as it should be.

a possible "/etc/hosts" could look like:

Code:

# Suppose the internal network to be 192.168.128/8
# Layout:  1-50 Infrastructure
#          51-99 Servers
#          100-  Clients

# ------------------------------------------------------------- Infrastructure
192.168.128.1      router router.mynetwork.org
# 192.168.128.2      printer1 printer1.mynetwork.org      # activate if you have a printer

# ------------------------------------------------------------- Servers
192.168.128.51      proliant1 proliant1.mynetwork.org
192.168.128.52      proliant2 proliant1.mynetwork.org
192.168.128.53      proliant3 proliant1.mynetwork.org
192.168.128.54      rasberry1 rasberry1.mynetwork.org
192.168.128.55      rasberry2 rasberry2.mynetwork.org
192.168.128.56      rasberry3 rasberry3.mynetwork.org

# ------------------------------------------------------------- Clients
# This only if you want to use static IPs for the laptop too
# 192.168.128.100     mylaptop mylaptop.mynetwork.org

So far, stay tuned for more. If you have questions, feel free to ask.

I hope this helps.

bakunin

It's OK to post photos when you post the image to your album and then post the internal bbcode for the image.

One big problem is posting an image from an external site, and then when the link is down or the image is removed from the image server, the link is then broken in the forums.

Images are ok when you need to post them, but make sure you upload the image to your image album on our site; and then post the BBCODE to the image.

Posting images based on links to external sites is not good; because when the external site changes, the image is lost and our links for future users are then broken.

Thanks.

bakunin - Thanks so much for your advice! It was quite elegant! I love that /etc/hosts file on all the servers!

Re pictures, I will look into how to do that Neo. I usually post to forums using Photobucket as my host, then I merely just put in a hard link to the .jpg using a tag: [lmg]url.jpg[lmg] /*replace the l for i*/ This is easy using my mobile.

---------- Post updated at 11:34 PM ---------- Previous update was at 10:25 PM ----------

Wow, just installed NoMachine on the Win and Linux machines. With all that great networking advice above from bakunin and a easy to use desktop share client to wrap it all together (NoMachine), I am thinking my questions are solved!!! Way to go Unix.com. Another amazing experience here. Time to get that Hadoop cluster up and running with some R and have a field day...

If anyone is interestes, NoMachine, free, uses SSH, and easy as pie to setup:
https://www.nomachine.com/

Neo - I was able to edit my image above to be hosted here, thanks for the tip, looks pretty easy to do also! Thanks for your work/commitment here!