VLAN vs Layer 3 Routing protocol

Unanswered Question
Jan 11th, 2009

I am confused in my network design. basically what we have is:

6 Cat Switches 3560E 1 per floor

2 Cat Switches 6509 (core switches).

The design is currently as the following:

each one of the 3560 switches configured with 3 VLANs.

And those VLANs goes to the core switch via EIGRP routing and not by using VLAN Trunking.

From what I understand is this is not optimal solution because the core switch (6509) will have to process packets in software bases. because the floor switches are announcing their VLANs as EIGRP routes.

Is this the best possible way to design the network? or do you recommend that I use VLAN trunks between the core switch and the floor switches?


I have this problem too.
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mahmoodmkl Sun, 01/11/2009 - 22:29


With these number of i would recommend to go for trunk links with transparent mode on the switches.



Jon Marshall Mon, 01/12/2009 - 12:30


"From what I understand is this is not optimal solution because the core switch (6509) will have to process packets in software bases."

This is not correct. 6500 switches and 3560 switch are L3 switches which mean they can route in hardware. Your 6500 switches will need to form EIGRP neighborships with the 3560 switches and this will not all be done in hardware but the forwarding of packets will be done in hardware. And a 6500 switch can very easily cope with 6 3560 EIGRP neigbors.

By using L3 links between your 6500 and 3560 switches you are using a routed access-layer and there is nothing wrong with this. You are removing the need to run STP across the access-layer links.

Either way ie. L2 or L3 uplinks is valid and neither could be considered non-optimal. If what you have works stick with it.


Roberto Salazar Mon, 01/12/2009 - 13:56

I agree with Jon, the packets are always hardware switched on cat6k, with a few exceptions which is outside the realm of this discussion. I would like to add that separating each floor at layer 3 is a better idea, in my opinion, that it also isolate each floor's/vlan's STP. If there is an issue with one floor's STP, the issue with STP would remain in that floor. Troubleshooting a routing issue for one segment is much easier than troubleshooting a L2 loop that has spread througout the network.


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