Switched L3 VS Conventional Router

[HEATH FREEL]

We have a network that currently uses a 7200 router for connectivity to the WAN. In the same network we have a 4500 Catalyst that has full L3 capabilities but is used for primarily for backbone switching. We are migrating to a MPLS network (etherent service) and the question has come us as to weather or not we should continue to use the 7206 for the WAN connection or go directly into the 4500.

Do the L3 switches have limitations as far as routing goes that conventional routers don't?

Can anyone give me reasons why I would pick one over the other?

[michaelhawkins]

There are several architectural and media considerations.

i) it is generally easier to maintain routing simpicity by considering your LAN environment to be a stub hanging off of all of your WAN connections. In particular, it is always easier to maintain a network when you minimize the number of transit networks. Therefore, it is generally easier to grow a WAN when your LAN is not a transit vector.

ii) Your 7200 is able to support many different types of WAN interfaces whereas your 4500 will only do Ethernet.

So if you take points one and two together you will generally reach the conclusion that the 7200 is the better place to terminate your new Ethernet MPLS connection. However, depending on the kind of NPE you have may alter your decision. For example, you might have a NPE400 or even less than that in your 7200. If that is the case, then you won't be able to take a Gigabit connection into your 7200. But your 4500 can. So then it becomes a dollar issue. Can you afford an NPE-G1? If you can, then you can get quite a few more years out your 7200 and you get to keep your network simple and easy to manage because you won't be making your 4500 transit networks.

Hope this helps.

MH

[michaelhawkins]

Oh, and you should also take into account that the 5500 is at Cisco end of life!

The 7200 will probably be following the 5500 into deadness fairly soon too but atleast it isn't dead yet.

If the WAN is expected to grow and the company/outfit is expecting to grow over the next few years then I'd go with the NPE-G1 and get a seriously beefed up 7200 that will take the outfit into the next five years without any capacity issues.

[Richard Burts · Accepted solution]

Heath

There is another aspect to consider about your question. There are services that we take for granted in router code which may not be implemented in L3 switch code. I recently ran into one of those when I realized that NAT was not supported on the particular L3 switch I was looking at. A quick look at the 4500 documentation suggests that it does not support NAT. I do not know how important NAT is to your implementation. But I would think about the kind of things that you are doing on your 7200, and the things that you may need to do in your new environment and check to be sure that those services are supported on the 4500.

HTH

Rick

[HEATH FREEL]

Rick,

Thanks for the reply. I recently did some more research and found the software advisor tool to give me a comparison of the features between a 4500 IOS Enhanced Image and a 7200 IP advanced service image. No comparision, the 7200 has far more features from a L3 perspective. I have decided to stick with the 7200 and probably upgrade the Processor to the 1G.

Heath

[Richard Burts]

Heath

I agree with your decision. And my experience with the 1G has been good.

This was a very good use of the software advisor. I have used it to compare different versions or different feature sets within the same platform. Using it to compare different platforms is not something I have done, but I think is a very good idea.

HTH

Rick