intervlan routing same as vlan trunking

Unanswered Question
Jun 20th, 2008

Hey Guys, got a silly question here.

I'm trying to work out a few vlans and to route each other on a centralised L3 switch.Do I need to configured vlan trunking in order to make the intervlan work?I had a couple of L2 switches which are connecting back to this L3 core switch.I'm trying to make the config simple as posibble.

I have this problem too.
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hennigan Fri, 06/20/2008 - 20:48

The inter-VLAN routing will take place on the layer 3 switch. You'll create VLAN interfaces there and assign IP addresses to the VLAN interfaces, route between them. The VLAN interfaces and routing protocols will configure pretty much the same as any IP-enabled interface and routing protocol on an IOS router.

To extend the VLANs to the L2 switches, you'll want physical interfaces on the L3 switch configured as L2 trunks containing the VLANs you want to extend to the L2 switches. Then on the L2 switches and for hosts on the L3 switch, you can configure access ports in the various VLANs as desired.

If you're familiar with "router-on-a-stick" configurations, think of the L3 switch as a giant router on a stick.

Richard Burts Sat, 06/21/2008 - 08:36

I might suggest a slightly different approach than Jay. First lets consider whether each layer 2 switch will have just a single VLAN configured on it or will have multiple VLANs configured on it. In the case where the layer 2 switch has just a single VLAN on it, then you do not need trunking from the layer 2 switch to the layer 3 switch. But if there are multiple VLANs on the layer 2 switch then I completely agree with Jay that you need trunks connecting the layer 2 switch to the layer 3 switch.



hennigan Sun, 06/22/2008 - 14:59

Rick is 100% correct. If all of the devices on any given L2 switch are in the same VLAN (and preferably in the same subnet -- secondary IP addresses get ugly fast), then no trunking is needed.


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