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What is a "Layer 3 Switch"? I essentially understand the OSI model, well maybe I don't and maybe that is why I don't understand. Its just that I don't see how/when/if a "managed switch" becomes a "layer 3 switch". Or, is a "managed switch" automatically a layer 3 switch?

  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide your own answer and accept it. – Ron Maupin Aug 7 '17 at 14:39
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Managed switches are in simple terms switches that can be "managed." Managed means that they can provide information/statistics about their operation and usually that they can be configured. While the vast majority of managed switches can be configured for IP (and this includes all the more capable devices with full feature sets), there are some that can be managed strictly over L2 with proprietary management software but this limits them severely in terms of what advantages they have over a non-managed switch.

A L3 switch is a switch that can perform some or all the functions of a router in addition to being a switch.

This then begs the question, what is the difference between a L3 switch and a router? Technically speaking, a L3 switch is a router. Or put another way, a device which performs L3 functions is a router (this is also why they can call consumer gateway devices "routers"), and a L3 switch performs L3 functions.

So why the distinction? People will point out many things sometimes, but you can always find exceptions to those (whether it is based on features, performance, etc). In my mind it really comes down to one thing.

L3 switches are designed first and foremost to perform L2 functions. Even if they have a full L3 feature set and high L3 performance, the primary motivation behind their design and engineering is L2.

Routers are first and foremost designed to perform L3 functions. Even if they have L2 modules or functionality, the primary motivation behind their design and engineering is L3.

So when it comes to pushing new capabilities, features and/or performance, the focus is often on their primary layer of operation first. An example of this was the Cisco 6500 L3 switch and the 7600 router. While they were both basically the same platform and could use much of the same hardware/modules, the focus was different.

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Layer-3 switches can route, too. Some layer-2 switches are managed so that you can change settings. All layer-3 switches are managed because you need to configure the settings.

Layer-2 switches only switch at layer-2.

Layer-3 switches can switch at layer-2, but they can also route at layer-3. Layer-3 switches don't necessarily have all the features of a router, but some are quite sophisticated.

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  • Now that helps. So are routers a layer 3 device? – Mark Christopher Nov 15 '15 at 4:35
  • Yes, routers are layer-3 devices. Hubs are layer-1, bridges (switches are bridges) are layer-2, and routers are layer-3. – Ron Maupin Nov 15 '15 at 4:50
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layer 3 switch and managed switch and layer 2 switch are different terminologies have some common features and some differences

  1. Layer 2 switch : is the device which can operate in the osi layer 2 and make its own switching decisions based on layer 2 address (MAC address) and may perform basic (QOS ,ACL)
  2. Layer 3 switch : is the device which can operate in the osi layer 3 and make its own switching decisions based on layer 2 address (MAC address) and make its own Layer 3 functions (routing,QOS,ACL and so on) based on Layer 3 address (IP address)
  3. Managed switch : both Layer 2 and Layer 3 must given IP to be managed so it is not necessary for a switch to be layer 3 to be managed , even layer 2 switches can be managed

other impotent question may you ask your self , what is the deference between L3 switch and Router where both operate in the same layer??

  1. Layer 3 switch has some thing called ASIC which enhance switching performance but Router not

  2. by default Router can perform Layer 3 functions more than Layer 3 switch (some dynamic routing like BGP not enable by default on L3 switch may need extra license but not default , route-map , object tracking and so on) but it is also depend on the vendor

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