Traditional router vs. layer 3 switch

[Kevin.Chapman]

Under what circumstances do you choose a router over a layer 3 switch and vice versa? I know routers using a store and forward technique, but do layer 3 switches do the same?

[Webmaster]

Every router these days is a store and forward router. Layer 3 switching isn't quite as efficent as routing. Layer 3 switches are simply switches that employ the use of a routing engine. Most routers have this functionality at their core with the exception of some modular routers like Juniper's M-series. I used to have access to an M7i which had a lower end RE-400. You could upgrade the routing engine on that model to a more powerful one.

Here is the deal with Juniper's M-series vs. Cisco's 6500:

The 6500 is ancient. I think something like 10+ old, but they are cheap, and perform pretty well. Definitely the most bang for the buck. However, it isn't the most effecient due the fact it's software (IOS) is monolithic and simply can't do the things Juniper does with JunOS.

It does however beat the Juniper on port density. Even the larger M chassis can't support the number of ports you can load into a 6500 chassis. Combine that with the fact you can basically use a 6500 for everything and the Juniper only shines as a dedicated router.

The 6500 can be used to hold full routing table with interior and exterior routing protocols, as well as layer 2 and layer 3 functionality. Many data centers are re-purposing their old 6500 hardware to be customer facing switches because they can cram 4+ modules of 48 port GE copper ports. The equivalent using 1U switches like 3750s or 4948s would cost more than double.

Try to cram that much stuff into the Juniper M-series. Sure you can do layer 2 on it, but for the price per port, you would be insane to do that. Bottom line, each case is different. There is magic solution and each device will beat the other in different situations.