OT-hijacked. . .Re: [K12OSN] Solving the bandwidth bottleneck

Les Mikesell les at futuresource.com
Thu May 12 12:55:05 UTC 2005

On Thu, 2005-05-12 at 05:15, David Whitmer wrote:
> I'm still trying to wrap my head around the
> differences between setting up a VLAN vs. just using
> multiple subnets on the same physical network.

Conceptually, separate VLANs act like physically separate
networks.  An extra tag is added to each packet to identify
it's VLAN and switches can either restrict access per port
to a single VLAN or permit everything on ports configured as
trunks.  Some equipment (routers and computers) can be configured
to connect to VLAN trunks and appear like they have as many
separate interfaces as you have configured VLANS.  You don't
need this but it is a cheap way to make a small router appear
to have as many interfaces as you have switch ports if you
need to keep a lot of different things isolated or route among
many unrelated subnets.  

> Is the primary difference that with a true VLAN you'd
> be using higher-end switches that are smart enough to
> prevent traffic from different VLANs from colliding
> with each other?  Is it possible to set up VLANs using
> consumer-grade network switches?

You need 'managed' switches which tend to cost at least twice
as much as unmanaged, but most manufacturers make them - you
don't need the super expensive Ciscos. 

In your case, though, I'm not sure I see any advantage of having
a private side at all since you really don't want to isolate
anything and the VLANs will end up sharing traffic on the same
wire anyway.   Why can't you convert the k12ltsp to a single NIC
model, giving out a chunk of your public range in DHCP and pointing
the default gateway to your real router?  That way thin clients will
still work from anywhere, you can add more k12ltsp servers and get
some load-balancing as mentioned in some other recent posts, and
you can use the same dhcp for boxes other than thin clients (having
to do static configuration on laptops that are used is several places
is painful).  If you care about the IP assignment to identify specific
machines, you can tie the DHCP address to the ethernet MAC address
in the DHCP configuration.  The only thing you'll lose is the
'full-auto' setup of the k12ltsp box since you'll have to tweak the
dhcp config to do what you want and you have to be sure you have enough
public addresses available.

  Les Mikesell
   les at futuresource.com

More information about the K12OSN mailing list