VLAN Help on 3Com 3250 and 4200 switches 2

[ITSurvivor]

Hi all, could someone help in how you would go about setting up VLAN using 1 3250 and 3 4200 switches. We had a consultant that left and never finished the job, so I am delegated to putting this VLAN together.

Each 4200 will be assign to a department, ie, Corporate-VLAN1, QALab-VLAN2, EngLab-VLAN3. I guess I will use the 3250 as the core switch.

Right now all 4 switches are hooked up as 1 VLAN using cat 5 cables on the 49 and 50 port.

Do I need a DHCP server for each VLAN and connected directly into one of the VLAN switch port?

I have read the 3Com documentation but that didn't really help and I also have search the Internet without much success.

Thank you all for your help.

 

[IRudebwoy]

No, you don't need a DHCP server connected in each VLAN. If your 3250 is the core you should enable the DHCP helper and enter the IP Address of the main DHCP server. If you VLAN'd the switches and config'd your DHCP server correctly the clients should get their addresses without a hitch.

Have Fun!

 

[ITSurvivor]

Thanks IRudebwoy for your reply.

If I enter the IP address of the DHCP server in the DHCP helper but the DHCP server is connected to one of the 4200 switch, is that's OK? Or should the DHCP server be connected to one of the port on the core switch?

Once I connect all the 4200 switches to the 3250, should I remove the daisy chain connection that is currently hooked up on port 49 and 50?

Sorry these questions are simple but I am trying to grasp the idea of how all these things work.

Thanks,

Richard

 

[globalchicken]

No thats fine. you can have your DHCP server connected to the 4200s but like cowboy said, you need the ip-helper address on every vlan interface except the vlan that the dhcp server is connected to. Logically it works like this: The PC will broadcast the vlan looking for an ip address from the dhcp server. Well the purpose of vlans are to segment traffic and control broadcasts. A device such as a L3 switch and a router will not forward broadcasts unless specified. The ip helper address will give the broadcasts looking for DHCP services a unicast address to point their requests to. Are doing Layer 3 switching or intervlan routing?

 

[IRudebwoy]

It should be alright if you have routing properly set up on the 3250. I don't think it matters where your DHCP server is plugged in. It just needs to be able to communicate with all VLANs (IP segments) it serves.

Yes, I would remove the connections on ports 49 & 50 but you will lose the gigabit uplinks. When in doubt, keep it simple.

Have fun!

 

[ITSurvivor]

Thank for the reply globalchicken. Now I understand a little more than I did before on how VLAN works.

On your question, I had to research it before I can answer you. We will be doing Layer 3 switching with the 3250 switch.

Is it difficult to configure VLAN with a Layer 3 switch?

Thanks,

Richard

 

[globalchicken]

No its not. I actually prefer that method over the traditional router on a stick.

Its quite simple..

example

Note: This is a config example from cisco.

Interface vlan 1
ip add x.x.x.x 255.255.0.0
ip helper-address (address of DHcP server)

This specifies that your vlan 1 interface has this ip and subnet mask and all pcs in this vlan will use int vlan 1 as default gateway.

interface vlan 2
ip add x.x.x.x 255.255.0.0
ip helper-address (address of DHcp server)

This is the config on the same switch using vlan 2. All ports in vlan 2 will use int vlan 2 as a default gateway. Now all routing between vlans is done on the switch using these 2 vlan interfaces to route between them.

Just ensure that you have your switches connected properly. If you have a switch dedicated for that vlan then ensure the uplinks from the core/distribution switch are in the same vlan of your access layer switch.

 

[ITSurvivor]

Thank you globalchicken and IRudebwoy for your time and great answers.

Globalchicken, sorry to be so dumb, but what do you mean by " If you have a switch dedicated for that vlan then ensure the uplinks from the core/distribution switch are in the same vlan of your access layer switch"?

And hopefully last question, where should the connection from our Firewall Trust Zone be connected to, the core switch?

Thank you both very much.

Richard

 

[globalchicken]

I was talking about this...

If you are designing 1 switch per vlan for your use, then you have no need for trunking. Just put the switchports in the correct vlan on both switches.

Then you can put your interface vlans on your L3 switch along with your ip helper address specifying the DHCP server address.

I did happen to put in 2 links from each layer2 switch to your core and if you are expecting high loads of traffic you could consider an etherchannel combining the 2 links and use them for load balancing. If this situation is not doable, then you could also consider configuring uplinkfast because your second link will be blocking as to not induce loops. Uplinkfast will allow your L2 link to converge faster and not wait 50 seconds for STP to converge.

 

[globalchicken]

For Firewall, consider adding an additional vlan on your L3 switch for internal connectivity and putting the firewall in a switchport that is associated with the new vlan. That way all traffic is segmented going to and from the firewall.

 

[ITSurvivor]

Thank you very much for all your help globalchicken. I feel more educated and ready to start this task. You and IRudebwoy have been most helpful.

Thanks,

Richard

 

[globalchicken]

NP I have actually never even configured a 3Com switch but its all theory, configurations just differ from vendor to vendor. If you could when you are completed with this project, could I see the output of your equivalent show run? I am curious to see the command set that is necessary...Thanks much

 

[ITSurvivor]

I certainly do that globalchicken.

Thanks,

Richard