Cisco 2950 dual Vlans

[mark.cooper]

I have 2 Cisco 2950 switches one for each network in my office. One switch is full the other only has 8 ports used. Since both swithches are 24 port I though I might be able to split the switch on the underused network and allocate 12 ports on it to the other busy network.

I assume I have to create 2 Vlans on the switch, but can I assign 1 vlan with the same IP as the other switch and simply patch them together.

[jrahm]

If you don't care about them being in the same broadcast domain, just patch them together, verify the trunk comes up, and leave all the interfaces in one vlan. Layer 3 segmentation doesn't require that layer 2 is segmented also.

[mark.cooper]

need to keep the two networks separtate

[ankurbhasin]

You cannot have same ip address for same vlan on 2 different switch if you want to connect the switch together because it will give duplicate ip address error message. yes you can have same subnet assigned for same vlan on 2 different switch.

If you are planning not to connect the 2 switches together and 2 switche will be isolated then you can play with same ip address on 2 switches.

HTH

Ankur

[jrahm]

You can keep the networks separate at layer 3 without separating the layer 2 infrastructure. If you want to keep them isolated completely, define vlan x and vlan y in both switches, and configure each port to be in one or the other:

int range fa0/1 - 12

switchport access vlan x

int range fa0/13 - 24

switchport access vlan y

Define each switch IP under int vlan x/y, depending on where you will manage it from. They can be in the same subnet, but cannot be the same IP.

[mark.cooper]

OK guys thanks for the help I think I got it now will play in the morning let you know how I get on

[sebastian.wiegand]

Hi Mark,

first of all i have a question.... Why do u need ip adresses on your switch? just to manage them?

If so here is my suggestion...

u should assign 3 vlans not 2... make one of them your management vlan and assing an ip addresses from a diffent subnet than your nodes. Then configure a trunk between the two switches. Remember to make your management vlan the native vlan (switchport trunk native vlan ).

Next u assign each port to the appropriate vlan and your done.

If u manage the switches via console port, forget about ip adresses... u dont need one. just make two vlans and assign the ports (dont forget the trunk).

Regards,

Sebastian

[hanwucisco]

Hi, I think the info you provided here is not enough for us to help you.

Whether or not vlans are need depends on the traffics, full ports may not be necessarily busy....

you'd better analyses your traffics then make a dicision.

[s.cui]

On a related note.. what if he wanted to route between the two VLANs. How would he accomplish that? Can he do it from within the switches or will he need a full fledged router to do it?

[Richard Burts]

If he wants to route between the VLANs he must get the traffic to a layer 3 interface. Since the 2950 is a layer 2 switch he can not route between the VLANs on the switch.

I am not clear what you mean when you say a full fledged router and whether you would include a layer 3 switch in that category. As long as the traffic gets to a layer 3 interface, then traffic can be routed between VLANs. It could be on a "router" or on a layer 3 switch.

HTH

Rick

[s.cui]

I guess what I meant by full fledged router, is having a totally separate piece of hardware like say a 1700 or something to route between the two.

If he has say a 2950G with EMI could he do it then? If a switch is layer 3 capable, can you employ ACLs just like you could a normal router?

[Richard Burts]

It would require a separate piece of hardware to route between VLANs. The separate hardware could be a router like a 1700 or it could be a layer 3 switch. As long as the separate device is layer 3 capable it can route between VLANs.

It would not change this question whether the 2950 had the standard image or the enhanced image. The 2950 is a layer 2 switch and can not route. With the enhanced image you get things like more security, advanced QOS, and high availability. But the enhanced image does not turn it into a layer 3 device.

HTH

Rick