[K12OSN] Two subnets

Thu Jan 11 12:02:05 UTC 2007

This is how I used to do x86, PPC, and UltraSPARC clients off of one
server.  It's certainly doable, but there are several things that you
get to modify:

/etc/dhcpd.conf
/etc/hosts
Some stuff under /opt/ltsp/

For /etc/dhcpd.conf, just copy 'n' paste your existing 192.168.0.0/24
scope, thus creating two scopes.  Wherever you see 192.168.0, replace it
with 192.168.1.  dhcpd is smart enough to know to hand out
192.168.1.0/24 addresses only on the interface in that subnet (I'm
assuming you'll use 192.168.1.254 for your server's new NIC).  Also,
make sure that you have a "next-server" setting in each of your DHCP
scopes that points to the appropriate NIC (192.168.0.254 for the
original scope, and 192.168.1.254 for the second, new scope).  That's
how your clients will know where to TFTP-boot from.

For /etc/hosts, you get to essentially replicate everything in there, in
a way that you avoid name/address resolution conflicts.  You know all
those entries that look like this?

192.168.0.9     ws009.ltsp      ws009

Well, you'll need to make 254 more entries to account for the clients on
the new (192.168.1.x) NIC.  But you can't have two "ws009.ltsp" entries
pointing to different addresses?  What do do?

My solution was to tweak the names so that my /etc/hosts has entries
like this:

192.168.0.009     ws0009.ltsp      ws0009

192.168.1.009     ws1009.ltsp      ws1009

192.168.2.009     ws2009.ltsp      ws2009

In my case, I simply added a digit to the hostname, specifically, the
third octet of the IP address.  A simple little script will generate
this for you:

****** CUT HERE ******
rm mynewetchosts.txt
for octet3 in `seq 0 2`
do
  for octet4 in `seq -w 1 254`
  do
    echo '192.168.'$a.$b'   ws'$a$b'.ltsp   ws'$a$b >> mynewetchosts.txt
  done
done
****** CUT HERE ******

Then, after backing up your original /etc/hosts (/etc/hosts.bak,
perhaps?), just copy this mynewetchosts.txt over to /etc/hosts.

Finally, we deal with /opt/ltsp/.  In my case, since my clients are
different CPU architectures, I needed /opt/ltsp/i386 (comes with
K12LTSP), /opt/ltsp/ppc, and /opt/ltsp/sparc.  Each of these
subdirectories served a different subnet.  Well, since all of your
clients are x86, then you get to have more than one "i386" directory
tree.  Why?  Yes, the binaries are the same, but you need to tell your
clients which IP address to talk to.  Just copy your entire
/opt/ltsp/i386 directory over to, say, /opt/ltsp/i386-1.  Head on into
this new /opt/ltsp/i386-1, and tweak lts.conf such that wherever you see
"192.168.0", you replace it with "192.168.1".  There should be only a
couple of spots, and, IIRC, the critical one is the "SERVER" variable.

Note that, in your second DHCP scope in /etc/dhcpd.conf, you will need
to tweak "option root-path" to point to /opt/ltsp/i386-1.  In my
/etc/dhcpd, I've got three scopes, one pointing to /opt/ltsp/i386, one
pointing to /opt/ltsp/ppc, and one pointing to /opt/ltsp/sparc.  The
reason you have to do that is because this is the directory that your
LTSP clients use to do the pivot-root.  In your case, each of your
/opt/ltsp/i386 and /opt/ltsp/i386-1 will be pointing to a different IP
address (NIC) on your LTSP server.

Once you're done, you should be able to turn up your second NIC, bounce
dhcpd, and have clients netbooting on your other subnet.

HTH,

--TP
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Michael Blinn wrote:
>  I have ~50 clients I'd like to split into two subnets, each on their
> own separate switches going into a separate gig NIC on the server. Out
> of the box, k12ltsp 5.0.0 likes to run on 192.168.0.0/24 right? What
> do I need to change in order to have a working LTSP configuration
> (complete with dhcp, tftp etc) on 192.168.1.0/24 in addition to the
> 192.168.0.0/24 ?
>
> If I can safely set both GB NICs on the same subnet, but separate
> switches, please let me know, however my initial thought is that the
> broadcasts will slow the system down by transversing switches via the
> server's NICs.
>
> -Michael Blinn
>
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