Broadcast filtering

Unanswered Question
Oct 12th, 2008

I am trying to set up a classroom network for a computer science class I am involved with. I wish to set up a closed environment within the school district network, so students can practice managing their own DHCP/DNS and not worry about effecting the performance of the district network. Currently I have a Cat2960-24-S and no router. Can I make this classroom environment work on a minimal budget?

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Giuseppe Larosa Sun, 10/12/2008 - 11:36

Hello Tim,

use different Vlans to partition the lab among students so that they don't disturb each other.

This is fine for testing DHCP and probably also to make a basic DNS test.

Let the vlans without a L3 routing service to the real school network to be sure they cannot be seen as rogue DHCP servers or rogue DNS servers causing problems.

Hope to help


timkunce0 Sun, 10/12/2008 - 11:41

Okay, would they be able to get out to the internet? I would like the students to be able to create something along the lines of a small office with DHCP, exchange, and possibly vpn (that would depend on the cooperation I would get from the school's IT people.)

Giuseppe Larosa Sun, 10/12/2008 - 12:15

Hello Jon,

no problem:

your post provides details about config that can help

Have a nice week

Best Regards


Jon Marshall Sun, 10/12/2008 - 11:44


It's not clear from your post as to whether this 2960 switch will be dedicated to the students or whether they will share it with other school users ?

The 2960 is a L2 switch only so it won't route. However a L2 switch will still support multiple L2 vlans and broadcasts are contained within a vlan. So you can select a group of ports for the students and allocate them all to a dedicated vlan ie.

2960(config)# vlan 10

2960(config-if)# name students

2960(config)# int range fa0/4 - 10

2960(config-if)# switchport access vlan 10

The above config would create a new vlan 10 and allocate ports fa0/4 - 10 into vlan 10.


timkunce0 Sun, 10/12/2008 - 12:02

The 2960 would just be for the students, I've been doing some research online. If I put that switch behind a 850 series router, would that allow me to set up my simulated work environment with internet access?

Giuseppe Larosa Sun, 10/12/2008 - 12:23

Hello Tim,

the answer is yes but be aware that if the 850 will perform inter vlan routing the different student groups may interact or disturb each other.

I don't know if an 850 can support VRFs but they could be helpful in isolating each group.

Or you can give internet access to a group a time

Hope to help


timkunce0 Sun, 10/12/2008 - 12:39

Thanks everyone for your help. You're answered all my questions fully.


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