[VLAN] VLANs and Network Emulation

[Ben Greear]

Hazelsnitzel wrote:
> Greetings,
> 
> My task leader wants to use a 24-port Cisco Catalyst 2950 in conjunction 
> with a Linux box to emulate multiple low-speed links, but I am too much 
> of a novice at networking and VLANs to know whether his idea is feasible.
> 
> We currently emulate a single low-speed link by interposing a Linux box 
> with two NICs between the endpoints on the link.  We use the Linux box 
> as a bridge and use Linux traffic control (i.e., tc HTB or TBF) and 
> "Netem" to emulate link characteristics. Eleven Linux boxes would be 
> required to emulate 11 low-speed links.  My task leader's idea is to use 
> a single "one-armed" Linux box and the 24-port 2950 to emulate up to 11 
> links.
> 
> The intranet in our lab uses OSPF and we are not allowed to increase the 
> number of router advertisements, so we can't use the Linux box as a 
> router.  However, if this constraint were removed, I assume (#1) that we 
> still couldn't use the Linux box as a router because both endpoints of 
> each link are always in the same subnet.  Is this assumption correct?
> 
> I also assume (#2) that we can't use the Linux box as a bridge.  I 
> assume that if the traffic emanating from the bridge were simply 
> returned to it on a trunked link, it would only forward frames to the 
> destination if the source and destination MAC addresses were in the same 
> VLAN.
> 
> I would like to know if my two assumptions are correct and whether 
> anyone has a suggestion about how to solve this problem.  Could it be 
> done by developing some custom forwarding software?   If so, what would 
> be required?

It can be done.  We offer a product based on VLANs and our (non-open-source)
network emulation tool.
I'm not sure if netem can be used in bridge mode though...

Here's a link to our 48-port network emulator product sheet (we offer other
quantities of ports as well):
http://www.candelatech.com/lanforge_v3/ct970_product.html

The diagram shows one LANforge machine and one bridge machine, but we can
now do all of this in a single machine for a more efficient use of hardware.

If you are interested in more information related specifically to LANforge,
please contact me directly (greearb at candelatech.com).

Thanks,
Ben


> 
> Thanks,
> 
> Bob
> 
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-- 
Ben Greear <greearb at candelatech.com>
Candela Technologies Inc  http://www.candelatech.com