difference between router & layer 3 switch

Unanswered Question
Jul 17th, 2009

Hi,

Please tell me difference between layer 3 switch & router.

Thanks in advance,

Regards,

suryakant

I have this problem too.
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Richard Burts Fri, 07/17/2009 - 07:58

suryakant

One of the traditional differences was that routers had a wider variety of interfaces for WAN traffic (there are few serial interfaces for switches). Another difference is that there is some functionality that is standard in router implementation but not in layer 3 switch. One example of this is address translation.

As far as general forwarding of IP traffic and support for routing protocols there is very little difference between a router and a layer 3 switch.

HTH

Rick

Jon Marshall Fri, 07/17/2009 - 08:02

Suryakant

In addition to Rick's post one of the main differences between a router and layer3 switch is that the functions of a router are primarily done in software whereas the functions of a L3 switch are primarily done in hardware with dedicated ASIC's.

So L3 switches tend to have much better performance although there are downsides such as the ones Rick pointed out.

Jon

fsebera Fri, 07/17/2009 - 08:07

Hey buddy,

The differences between a router and a switch have become very blurred over the years. As you already know, originally a switch was just a multiport bridge. And a bridge just segmented layer-2 domains. Original switches mainly just added additional number of ports as bridges only had small number of ports.

With the advent of switch VLANs, a router was required to allow different vlans to communicate and in early models, this was slow at best (in reference to todays layer-3 switching).

Now the routing functions have been combined into the same box and this new box is called a layer-3 switch. This new layer-3 device performes the same tasks as the bridge/switch and router combined.

Why you would install a router verses a layer-3 switch depends on your networking environment.

You may consider consulting a networking engineer for additional help.

HTH

Frank

wilson_1234_2 Fri, 07/17/2009 - 12:29

In addition to the great experts above,

The QoS capabilities for Layer 3 traffic management, are much more in depth and granular on a router than with a layer 3 switch.

huangedmc Fri, 07/17/2009 - 21:43

From what I've seen, routers provide better feature sets, such as NetFlow, WCCP, and QoS, while L3 switches provide better forwarding performance.

Some L3 switches also support Netflow, wccp, and QoS, but the support is rather limited.

One exception is the 6500 line, which just supports about everything that routers do.

Joseph W. Doherty Sat, 07/18/2009 - 05:15

"One exception is the 6500 line, which just supports about everything that routers do."

"just ... about" is something not to miss. As feature rich as the 6500 series (or its "router" variant, the 7600 series), and even including some special hardware (e.g. sup32-PISA, FlexWAN, SIP-200/400), generally a software router will sill have additional features.

As others have already noted, most router features are delivered by software (although sometimes with special hardware assist) and most L3 switch's features are mostly supported by hardware with software assist. Dedicated hardware delivers wonderful performance, but often more limited features.

To provide an example of the performance differences, the largest ISR, the 3845, is rated at 500,000 pps, while a 24 port 3560G is rated at 38,700,000 pps, and I believe, costs less.

Sushil Kumar Katre Sun, 07/19/2009 - 20:55

Hi Suryakant,

You have got a great amount of information here on the difference.

I would not write technical difference anymore, but when I started with my CCNA classes, for first few days the only difference between a router and switch (didn't knew there is something called a layer 3 switch during those days), which I knew was -

Router is Circular and Switch is Rectangular :)

When I enetered the lab we were asked to identify routers from a pile of devices, and I remember saying there is no router out theres, because I was looking for a circular device :)

-> Sushil

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