[K12OSN] LTSP on same network as Windows

Sat Aug 21 20:28:58 UTC 2004

Jeff Kinz wrote:

>On Sat, Aug 21, 2004 at 08:31:40AM -0400, Yancey B. Jones wrote:
>  
>
>>I am going to be setting up a Linux terminal server for a charter school
>>here in Cincinnati. The idea has been extremely well received by the school
>>administrator. We will already have a DHCP, DNS, and Internet gateway in
>>place before setting up the terminal server so is there any reason that I
>>shouldn't set up the Linux terminal server on the same network and use my
>>existing DHCP and DNS servers? I will also want to give students/teachers
>>access to their files whether they log into a Windows box or Linux terminal
>>- any HOWTO's for this come to mind?
>>    
>>
>
>
>TC's (Thin Clients) use a lot of bandwidth between themselves and their
>respective LTSP server.
>
>You should definitely think about having your TC's on a separate LAN
>segment with their server.  The server can act as a gateway to the rest
>of the LAN by giving it two NIC's.
>
>This will reduce the load on the rest of your LAN by moving all the TC
>specific traffic off of it onto this separate network segment.
>
>
>This will also eliminate the confusion between your LTSP server trying
>to act as DHCP server for your TC's at the same time your original
>DHCP server is trying to do the same thing.
>
>Since the k12ltsp distro is setup to have the LTSP server be the dhcp
>server for the TC's this will make your life easier as well.
>
>  
>

Depends.  "Layer 8" might end up getting in the way.  If his district is 
anything like mine, there is exactly *one* DHCP server allowed on any 
school's LAN.  Fortunately, in my case, I control it.  :-)  However, it 
did put me in a similar situation of running a K12LTSP server on the 
same LAN as the Windows LAN.  Turns out that, on a switched network, the 
bandwidth issue raised above is not a problem.  Remember that switched 
networks allow point-to-point communications, so the Windows boxes will 
never see all that X11 traffic between the thin clients and the server.  
This has been my experience.  Just make sure that your client NICs and 
your switches support autonegotiating to 100Mb/FullDuplex (virtually all 
do these days), and don't lock down any of those ports to 100/Full--let 
them autonegotiate normally (virtually always the default).  It's a lot 
easier, believe me.

Here's how to do it.

Build your server with a single NIC (needs to be Gig-E).  If your 
motherboard comes w/ two NICs, pick the Gig-E one.  CAUTION:  Do *NOT* 
connect this server to the network yet; you will hose the entire LAN 
(you'll find out why here in a minute).  Install K12LTSP as you normally 
would, making sure that eth0 is the Gig-E NIC.  So far, so good.  Go 
through your reboot procedure, make your non-root userID like you always 
should, and then turn off DHCP on the K12LTSP server.  How do we do 
this, you ask?  Here's how.

  microman at multimedia:~$ su root
  Password:
  root at multimedia:/home/microman# /sbin/service dhcpd stop
  root at multimedia:/home/microman# chkconfig --level 2345 dhcpd off
  root at multimedia:/home/microman# exit
  microman at multimedia:~$

Now that you've turned off that DHCP server, go ahead and connect your 
new K12LTSP server to the LAN.  If you had hooked up your server 
beforehand, you'd have had a DHCP server giving out possibly incorrect 
IP addresses for your school's IP subnet to the Windows boxes!  For 
example, my schools run 10.x.x.x addresses.  Handing out 192.168's 
(K12LTSP's default) to the Windows boxen on the LAN would not be 
received well.  I made that mistake once w/ a DHCP server about four 
years ago.  Took down nearly the entire office.  Oops.

Of course, now we have to tweak the existing DHCP server to hand out the 
TFTP boot and the NFS pivot-root directories.  How, you ask?  Well, on 
my LANs, we use Cisco routers as the DHCP servers, and here is the 
config I use here at home:

ip dhcp excluded-address 192.168.0.0 192.168.0.10
ip dhcp excluded-address 192.168.0.250 192.168.0.255
!
ip dhcp pool InsideAddresses
   network 192.168.0.0 255.255.255.0
   bootfile lts/vmlinuz-2.4.18-ltsp
   next-server 192.168.0.254
   default-router 192.168.0.1
   dns-server 192.168.0.254 198.6.1.3
   domain-name cmosnetworks.com
   option 17 ascii "192.168.0.254:/opt/ltsp/i386"
!

These same parameters need to go on your DHCP server, whatever it is.  
"Option 17", BTW, is the DHCP option (I had to specify the raw option 
number) in which you tell your thin clients your NFS path, a.k.a. your 
"root" path.

--TP
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