Cisco router and 3 layer switch

Published on January 14 2014 by dellpe

Question:

I am really really confused with this. It is said that router's are more based on software thus they're slow compared to switches. Switches are more hardware based, and are very fast. Then why not make one device do all of the routing and switching. Why is there such a need for routers? I guess it could be made that you can produce a single unit that does it all...Is all of this marketing strategy of Cisco?

Answer:

Although you would think of making one device to do all routing and switching functions, such a device likely will not be the best at doing both. Switches are faster than routers by virtue of their features being implemented in hardware; hardware switching being faster than software switching. Although some switches are modular, they do not support as many different interfaces as routers do. Routers can connect heterogeneous networks with various interface types and the features to support these different interfaces are implemented in software. All in all you’ll likely end up needing a mixture of both routers and switches to collectively achieve your routing and switching requirements.

The reason we are able to develop fast switching devices is two fold - and I am talking about pure L2 switching right now.

Nothing needs to be modified
Only one type of data is being handled - Ethernet

Even at layer 3 operations, a standard switch handles Ethernet frames

While a router is meant to be able to process frames 'originating | destined' for more than one kind of encapsulation - frame relay, ppp, MPLS etc
Add to that the fact that the router has also got to convert a frame from one format to another, if required

At layer 3, again, a standard switch handles Ethernet frames
A router is also supposed to inspect the frames at a much elaborate manner than a L3 switch, VPN possibly

At layer 3, a standard switch handles Ethernet frames
A router may be required to inspect the frames at a much more deeper level and perform an analysis, 'IDS | IPS' perhaps

7. Coming back to switching again. Standard L3 switches(for example WS-C3750X-48T-L ) would be slower than another series of L2 switches manufactured by Cisco - namely Nexus.

8. The Nexus series is super fast compared to Catalyst, but it is specialized mainly for operations such as data centers & has its own limitations.

9. So, now you have Nexus - super fast, L3 Catalyst - Very fast & L3 Cef enabled Routers - Fast.

10. As can be made out, it is mainly

the kind of data that a device handles,
that dictates the kind of hardware that can be developed for it
That in turn decides the kind of speeds that it can achieve