Now the router wants to send a packet to 192.168.1.1. Now in this example, you have two switches plugged into the back of this internet router. that 4 port switch is already wired to the router's port. Think of the internet router as two devies, a router and a 4 port switch in one box. You can plug additional switches in that back of this internet router. On an internet router that has 4 ports in the back, this internet router is actually a router with a built in switch. Do not confuse a traditional router with that of a consumer based internet router that has many ports on the back of the box. A router wouldnt have more than one NIC that belongs to multiple subnets. So first, generally if a router has more than one NIC, each NIC is on its own subnet. The purpose of the switch is to move packets at a layer 2, unlike the hub which is layer 1 and has no knowledge of MAC addresses. Neither the computer, nor the router really know that the switch is in its way. So as you see, the switch is just in the middle of this path. All other computers will discard the packet.ġ3) target computer will process the packet and send a response back to the router (process is reversed now)ġ4) on the way back the switch has now learned (if #10 was true) about the computer's MAC, switch updates its table. The NIC that has the same MAC address will bring the packet up to the OS. The switch picks up the packetĦ) Switch is a layer two device, doesnt care about the IPħ) switch looks at the packet to inspect the destination MAC.Ĩ) Swich looks at all MAC tables to see if it can knows which port the MAC has been seen.ĩ) if the Switch finds the MAC in its tables, it send the packet on the correct portġ0) if the switch does find the MAC, then it sends the packet on ALL of its portġ1) If #9 is true, the destination computer will receive the packetġ2) if #10 is true, all computers receive the packet. This interface is connected to the switch port. If it doesnt, it performs an ARP request until it gets the answer.ĥ) packet is own its way on that interface. So here is what happens in the scenario where the router needs to send a packet to computer A:ġ) router has a packet that it needs to deliver to 192.168.1.1Ģ) router determines that to get to this host it needs to send the packet on interface 1 (based on the router's routing table)ģ) router checks its arp table to see if it has a MAC address for host 192.168.1.1Ĥ) if router has MAC, it sends the packet on that interface. so if the router needs to send a packet to 192.168.1.1, it knows that that subnet is on the router's first interface, as an example. The router may be connected to more than one switch, but it each switch will be on a different router port and VLAN.
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