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Dave avatar Server

Layer 2 Network vs Layer 3 Network

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Dave

I am very new to networking world and forgive me if its a lame question - My question is even though network operate using all 7 layers present in OSI model, often I hear people asking is it layer 2 network or layer 3 IP based network. Why is that? I understand the difference between layer 2 and layer 3 (packet vs frames)

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Michael Hampton avatar
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Michael Hampton
What is the context here?
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Dave avatar
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Dave
My question is even though network operate using all 7 layers present in OSI model, often I hear people asking is it layer 2 network or layer 3 network. Why they ask it is layer 2 network or layer 3 network
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Greg Askew
Plenty of documentation available on the topic: http://tcpipguide.com/free/t_NetworkLayerLayer3.htm
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Dave avatar
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Dave
@Greg Askew As I mentioned - why people ask whether it is IP based network. All networks will have network layer too
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Michael Hampton avatar
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Michael Hampton
You didn't explain the context. Who are these people you keep hearing? Why are they asking that question?
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Tom Yan avatar
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Tom Yan
Many VPN implementations don't even "virtualize" L2. They do not make use of ARP to "resolve" some nexthop / gateway IP to a destination MAC address. That's probably one of the cases in which terms like IP/L3-based/only might be coined.
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Dave avatar
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Dave
@TomYan you mean there is no layer 2. data goes from layer 3 to layer 1 ?
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Dave avatar
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Dave
@MichaelHampton - These people are network specialist. They ask this question to explain the network setup
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Tom Yan avatar
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Tom Yan
@Dave No, the OSI model is nothing but a conceptual reference these days. The statement `network operate using all 7 layers present in OSI model` isn't even precisely true. These days when people say "L2" they are mostly referring to switching / Ethernet frames etc., but in for example virtual network, there's only the VPN implementations themselves and they do NOT work directly on top of a physical layer. You should take a look at the layering of TCP/IP: https://en.m.wikipedia.org/wiki/Internet_protocol_suite
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Tom Yan avatar
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Tom Yan
@Dave In some VPN (e.g. tap mode OpenVPN), an L2 might be virtualized; if you have to fit the implementation to the OSI model, it will then be a bit *analogous* to an L1 (which is even more absurd since it's not physical / hardware at all).
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t3ln3t avatar Server
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t3ln3t

A layer 2 network only cares about the MAC address presented on each port and is a usually a single broadcast domain.

A layer 3 network encompasses the IP configurations as well as the MAC addressing for each node on the network. They often can handle inter-domain routing between vlans and broadcast domains.

The main difference between a layer 2 switch and a layer 3 switch is the routing function. A layer 3 switch is smart enough to route traffic between subnets and vlans without involving a device that functions as a router.

Many smaller networks function just fine using only layer 2 switching. As your network grows and becomes more complex, there will be a need for a layer 3 network. When you have many networks, multiple subnets and over 1024 hosts you will have to implement true layer 3 networking.

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