Internet access and multiple VLANs - Advice!!

March 30, 2010 at 21:03:08
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Hi guys, I need a bit of advice. I have a client with a flat network with all devices on VLAN1 (192.168.0.0/24). Currently internet access is acquired by all clients having their default gateway set to 192.168.0.15, which is the LAN interface of a Cisco 2800 router. I am implementing a new network core consisting of 2 x L3 switches with multiple VLANs. The Cisco router will retain its IP address on VLAN1 but all clients and servers will be moved to separate VLANs on the network core. My question is how can I retain internet access via the router in VLAN1 when all clients will now have their default gateway set to the appropriate IP interface on the network core? I have a Visio diagram which I can send if anyone can offer assistance as I'm a bit stuck.

Thanks!!


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#1
March 31, 2010 at 08:29:06
You could post your diagram on an online photo site like photobucket and then paste the link in a response.

Typical setup in a multiple VLAN environment uses the default, VLAN 1 as the management VLAN.

You would use your management VLAN and it's associated subnet to address all network appliances. This VLAN is used for no other purposes (ie: client IP's etc).

You already have your gateway, the 2800 router, configured with a "management VLAN" IP adress (192.168.0.15) on the internal interface. From what you write, it looks like you have everything setup and working with regard to accessing the internet.

The simplest scenario would be to assign those two switches IP's in the same VLAN
example:

Switch1:
IP: 192.168.0.20
SM: 255.255.255.0
DG: 192.168.0.15

Switch 2:
IP: 192.168.0.21
SM: 255.255.255.0
DG: 192.168.0.15

Once you have your management VLAN and all appliances connected to it, communicating properly you can begin creating your new VLAN's.

Each VLAN will be a unique subnet and will have it's own gateway IP associated with it. You will then need to create routes from the new VLAN's to the management VLAN in order to provide them with external connectivity.

Example:

VLAN 2 = 192.168.2.0/24
SM: 255.255.255.0
DG: 192.168.2.250

VLAN 3 = 192.168.3.0/24
SM: 255.255.255.0
DG: 192.168.3.250

VLAN 4 = 192.168.4.0/24
SM: 255.255.255.0
DG: 192.168.4.250

We use .250 as our default gateway for every subnet here where I work so I used that in this example. You can set whatever standard you wish.

You'll also notice I made the VLAN tag match the subnet. It's a handy idea that makes things easier to remember. If I were you, before I did anything else, I'd change VLAN 1 to 192.168.1.0/24


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#2
March 31, 2010 at 08:38:39
How many pcs/servers do you have?

You only mention one class c subnet so I have to question why you are appling enterprise criteria to such a small network.

Do you also understand you only need a layer 2 managed switch to do vlans? Layer 3 is more expensive since it also includes ip routing.


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