Originally Posted by
BillyCarpenter
Now let's talk about routers and the role they play in INTER-VLANS.
Keep in mind that VLANS are at the switch level (layer 2) and they are separate networks that can't communicate with each other. But what if you want to communicate between the different VLANS? In order to do this we need a router. Unlike switches, routers care about IP addresses (layer 3). It's important to keep this in mind before I explain how inter-vlans are possible....
....If we have a PC on VLAN 1 it may have an IP address of 192.168.10.2. On VLAN 2 we may have another PC with the IP address of 192.168.20.2. In other words, PC's on different VLAN can't have the same mask, or subnet. That would kind of defeat the purpose.
Anyway, the PC sends the packet to the switch, the switch looks in it's VLAN table and has no way of sending the packet between 2 different VLANs. What happens next is the packet is sent to the router. Keep in mind that the path between the switch and router is connected by a trunk line thusthe VLAN tag (encapsulation 802.1Q) hasn't been stripped away and is still present. Once the packet reaches the router, it has it's own table that it looks at. This table is a different from the table found at the switch. This table binds the VLAN to an IP Address.
I'll admit that's a little confusing and took me a while to grasp.
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