Is it possible to have a Switch acting as a Hub?

[jmguzmanc]

We require to have several computers listening to (unicast) packets from a server, while seeing each other.

Initialy we tried by using SPAN sessions, but only one destination por is allowed. Now we are trying with RSPAN, but it doesn't seem to work.

- Is there some way to have several ports, listening unicast traffic from one port? Some special config at FIB level?

- Under this scenario, is possible to keep all ports switching? (computers also require see each other)

My basic solution is to use a hub, but they are hard to find devices, today..

Any help will be appreciated.

Thanks

JM

[scottmac]

NO. Switches is switches, hubs is hubs.

That means:

Hubs are baiscally a multi-port repeater .... every bit coming in is concurrently clocked out every other port.

Switches are basically multi-port bridges. Unicast frames are only sent out the destination port. The only exceptions ae multicast (includes broadcast) frames and "flooded" frames (when the switch/bridge doesn't have an entry for the destination MAC, it's flooded out every port.

Floods are different then broadcasts or multicasts in that the destination MAC address remains the same and is sent out every port .... a broadcast frame is all "ff" (all ones) and a multicast frame has a specific multicast MAC address.

Again, the bottom line: No, you can't normally make a switch look like a hub ... they operate at different levels of the OSI model, they are different, they are designed to be different.

There used to be a bug that when you overloaded a Cisco switch it would flood all frames (essentially go into "Hub Mode." I'm sure that's been fixed by now.

Good Luck

Scott

[jmguzmanc]

Thanks Scott.

I am going to buy a hub...

Regards

JM

[Richard Gallagher · Accepted solution]

Well it depends on the switch you are using. With a cat6500 and the latest 12.2SX you can disable mac-address learning per vlan, hence you should get unicast flooding across that vlan.

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/122sx/cmdref/i1.htm#wp1873107

This might help you achieve what you want.

HTH, Rich