VLAN design

[adventurem]

I am currently working on a large corporate network replacing its legacy equipment with new Cisco devices. I am debating on what the best design would be for laying out the VLANs. In the past Cisco has recommended using end to end VLANs which seems outdated. Currently their network consists of hubs with large broadcast domains.

The newer designs seem to push creating a single VLAN per switch, but there seems to be little documentation on best practices or recommended designs. The goal is to use 4500 series switches at the access layer and a pair of 6509s at the core/distribution. IP telephony will also be used in this network.

I am simply looking for your opinion or links to any material that may be helpful.

Thanks in advance

[a.awan]

There are differing opinions and unfortunately the correct answer is 'it depends'. However, i will give you my opinion and that will be to have a separate VLAN per access switch or access switch block. By access switch block i mean any cascaded switches that you might have to place in an IDF. I tend to avoid L2 links between the Core switches thus removing any loops and thereby possibly avoiding any STP related issues in the future. It also is easier to troubleshoot for the support staff and with newer features coming out (like GLBP) load balancing is also easier to implement.

Most of the times you will get a requirement in which case you have to span a VLAN across multiple switches and end up having a L2 link between the cores. In such cases my personal approach is to keep this both physically and logically separate from the L3 link (just a personal preference). You will still be avoiding loops for all your other VLANs becasue of the L3 link. You have to make sure that you only allow the exceptional VLAN(s) on the L2 link (can be a trunk if required).

One thing you should work out before finalizing the design is a VLAN allocation standard and stick with it. Consider things like Data VLANs, Management VLAN(s), Voice VLANs, any VLANs required for point to point links acting as L3 links, etc.

Hope this helps.