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Re: [K12OSN] Network Bandwith

Ok, I was making several assumptions that I perhaps should not have been
making.  Namely:

- There is an existing network consisting of Macintosh and/or Windows PCs,
  file servers, networked printers, and an internet gateway.
- The desire is to integrate an K12LTSP install into that network without
  disturbing it.

I've mainly been experimenting with K12LTSP at home, and from the few
installs that I've done, it appears to default to using two nics in the
LTSP server.  One for your LTSP network and one for the existing network.
This makes sense, and seems the most likely initial configuration for a
school starting to experiment with the K12LTSP project.

In this configuration you'd actually have two seperate networks connected
by a router (in this case, the K12LTSP server).  The K12LTSP server does
NAT for the terminals and acts as a gateway to the rest of your network.

It is definately true that the terminal network will have a great deal of
traffic.  Just the overhead from X is considerable.  Add to that the
additional bandwidth required for the applications, sound, NFS swap, TFTP,
etc., and you can quickly saturate an inexpensive 100 mbit ethernet
switch.  If you anticipate having lots of terminals off of a single large
server and you've got the money, go for a high end managed 100 mbit switch
with a gigabit uplink for your server(s).  Such a switch can easily cost
10 times or more what something like a Linksys 24-port 10/100 unmanaged
switch costs, but it can also actually provide a full 200 mbit/s of
throughput (100 mbit full duplex) to every port on the switch

However, in such an environment as I've described above, the bulk of the
network traffic for the K12LTSP install is limited to the terminal LAN and
does not cross over to the pre-existing network.  In this scenario they
are seperate physical networks that are joined by the K12LTSP server.

Now, some traffic obviously would cross over to the existing network.
Any internet traffic would be one example.  Printing to networked printers
on the pre-existing network would be another.  Your non-terminal users are
likely to want to share files with the terminal users, which is yet
another source of traffic on your pre-existing network.  Still, this
traffic should not be a major impact.

By default the K12LTSP server assigns IP addresses in the (IIRC) range of
192.168.0.x via DHCP to the terminals.  This is a non-routed IP range.
In order for the LTSP terminals to talk to the pre-existing network (or
any other networks attached to the pre-existing network, e.g., the
internet) the server (which is actually acting as a router in this
scenario because it's joining two physically seperate networks) has to be
doing NAT.

It was not my intent with my original message to suggest that there would
be little to no impact on a pre-existing network regardless of
configuration.  In fact, if you run the terminals on the existing network
without physically seperating the terminals off on their own network
(which is certainly possible), then there would be a significant impact on
the existing network.  However, from what limited experience I've had with
the default configuration of a fresh K12LTSP install (in which the
terminals are physically seperated from the pre-existing network), it
appears that the pre-existing network should not be significantly


On Fri, 8 Nov 2002, Steve Wright wrote:

> jeffr odeon net wrote:
> >Also, the default K12LTSP install uses the server as a NAT/gateway for the
> >clients to get to the rest of your network.  In this scenario you seperate
> >your terminal traffic from the rest of your lan, so the impact on your
> >existing network can really be pretty minimal.
> >
> It looks like it doesn't it..  8-)
> remember, there are no applications running on the terminals..
>  everything runs on the server.  The server simply "paints up" the
> terminal window to complete the illusion.  8-)
> Therefore, from the terminals, there is no NAT involved.  The only
> traffic on the terminal LAN is X (unless you have network printers etc..)
> If you have win boxes, you will have to turn NAT on so they can get to
> the 'Net.
> see..  8-)
> /steve
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