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Layer 3 switch vs. Layer 2

Last Modified: 2012-05-05
We are looking into moving to VoIP to connect our 3 locations and each of the vendors we have looked at quoted the system with layer 3 POE switches.  Once we negotiate further they have all been willing to drop to layer 2 switches to cut cost. I understand what POE does but need clarification between a layer 2 and 3 switch.  We are a fairly basic network with a T1 based WAN.  We currently are not utilizing VLANS or any advanced configurations on our switches.  Thats not to say we wont in the future but I am trying to determine if layer 3 is something we should be looking at.  In the VoIP process we will be moving to Cisco 2811 or 2821 routers with the voice bundle.
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In a nut shell, layer 3 switches have routing capabilities where layer 2 switches do not.  Did they give you the model numbers of the different switches they are planning on using.  


The model usually quoted is Cisco 3560 POE.  
A layer 3 switch is basically a kind of router that tends to operate at a much faster rate.  Layer 3 comes from the fact that it operates at the internetworking layer which in TCP/IP networks means that it understands IP addressing.  Layer 2 switches work with MAC addresses.  This means that there is no separation of subnets using a layer 2 switch unless you also use VLANs.  Layer 3 switches basically route IP packets.  They are much more expensive than layer 2 switches and are generally used for different needs.  If you only have a single subnet then a layer 2 switch is fine.

Note that becaue layer 3 switches understand the IP protocol, they can also make traffic decisions on the basis of the IP packet, for example prioritising VoIP traffic.


Each of our locations is in it's own subnet linked through the WAN.  But since we have routers doing the routing, do we need layer 3 capability at the switch.  Are there advantages in the VoIP world to doing that?  All of the vendors we have quoted through are willing to drop down to layer 2 switches so I am trying to detemine if they are just trying to sell a more expensive switch or if we can use layer 2.
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What you shouldn't do is use a layer 2 switch to join these subnets unless you are also using VLANs to separate them, otherwise they'll all be present on the same LAN and you may get other issues.

From the sound of your last post it sounds like they are trying to sell you something you do not fully need.  From the sound of your Footprint it is pretty flat.  How many nodes do you have on the full network? how Many items are you looking to replace?
You don't need it, you could use layer 2 switches.

I agree.  You can do what you need with a layer 2 switch.  A layer 2 switch operates identically to a simple network hub, but with better performance, for almost all purposes.
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