Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Cisco Employee

Can I create a 'virtual hub' on one single VLAN?

In a network of Cat6k switches trunked together, can I effectively disable switching on a particular VLAN, so that all packets on that VLAN, regardless of destination MAC address, get flooded to the whole VLAN? I want to maintain proper switching function on my other VLANs, but create a 'virtual' hub on this one particular VLAN. Is it possible, and if so, how? Thanks.

4 REPLIES
Cisco Employee

Re: Can I create a 'virtual hub' on one single VLAN?

You can. Check the following page

http://cio.cisco.com/univercd/cc/td/doc/product/lan/cat6000/sw_6_3/cmd_ref/setsn_su.htm#35754

But be aware that network meltdowns can occur due to Loops with STP disabled

New Member

Re: Can I create a 'virtual hub' on one single VLAN?

No you can't. disabling SPT will not make this happen. connect a hub to the switch and connect the users to that hub.

what are you trying to achieve anyway ?

Cisco Employee

Re: Can I create a 'virtual hub' on one single VLAN?

We have a team of engineers developing software for the 6kNAM blade (RMON/Network Analyzer). Each engineer prototypes code on his own blade in his own switch. We only have one Gigabit traffic generator (Smart Bits). I wanted to set it up such that any test traffic generated by the SmartBits gets to ALL switches, so each developer can see if his code handles it. Gigabit hubs can be expensive, and we already have the switches. So I figured we could create a special 'Test' VLAN that does not get routed anywhere outside our lab, but gets flooded to all the switches in the lab. Other VLANs must be switched/routed normally. It's not a typical scenario, that's for sure.

New Member

Re: Can I create a 'virtual hub' on one single VLAN?

Basicly what you need to do is prevent the 6K from learning addresses on the ports and you will have a switch that will flood all packets for unlearned MAC addresses.

If you creat a "test" VLAN then creat a filter using the command:

set cam {static | permanent} filter {unicast_mac} vlan

Do this for ALL the MAC address of the devices attached in the "test" VLAN. Since the switch can no longer learn the mac addresses for the devices it must FLOOD any packet with that destination out all ports in the VLAN giving you a "virtual HUB".

Hope this helps.

186
Views
0
Helpful
4
Replies
CreatePlease to create content