The layer 2 address is a physical address.
Layer 2 vs. Layer 3 addressing - Cisco Community
It pertains to the actual hardware interface NIC in the computer. A computer can have any number of layer 3 addresses but it will only have 1 layer 2 address per LAN interface. At layer 3, the data is addressed to the host that the data is destined for. At layer 2 though, the data is addressed to the next hop.
This is handy because you only need to know a host's layer 3 address which can be found out by using DNS for instance but you won't need to know the hardware address and you won't have to bog down the network by sending an ARP request across the internet to find it out. The layer 3 packet addressed to the destination host will be encapsulated within a layer 2 frame addressed to the next hop. When the data gets to the Network layer it will put on the destination IP address. All of this info the network layer datagram, aka packet is passed down to the data link layer where it is taken and placed within a data link frame.
Based on the IP address and the subnet mask , your computer should be able to figure out if the destination IP is a local IP or not. Since this request is broadcast, all machines on the LAN will receive it and examine the contents. If the IP address in the request is their own, they'll reply. On receiving this information, your computer will update it's ARP table to include the new information and will then send out the frame addressed with the destination host's MAC address. The router will look in it's routing table and if it has a route to the destination network, then it will reply with it's own MAC address.
This is only the case if your own computer doesn't know anything about the network topology.
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In most cases, your computer knows the subnet mask and has a default gateway set. Because of this, your own computer can figure out for itself that the packet is not destined for the local network. Instead, your computer will use the MAC address of the default gateway which it will either have in it's ARP table or have to send out an ARP request for as outlined above. When the default gateway router receives the frame it will see that the MAC address matches it's own, so the frame must be for it. The router will un-encapsulate the data link frame and pass the data part up to the network layer.
At the network layer, the router will see that the destination IP address contained in the header of the IP packet does not match it's own remember, the IP address has not been touched at all in this process since your computer created the IP packet. The router will realise that this is a packet that is supposed to be routed. The router will look in it's routing table for the closest match to the destination IP in order to figure out which interface to send the packet out on.
When a match is found, the router will create a new data link frame addressed to the next hop and if the router doesn't know the hardware address for the next hop it will request it using the appropriate means for the technology in question. The data portion of this frame will contain the complete IP packet where the destination IP address remains unchanged and is sent out the appropriate interface.
This process will continue at each router along the way until the information reaches a router connected to the destination network.
2013 MacBook Air WiFi Problems (high latency, dropped connections) [Updated]
It will see that the packet is addressed to a host that's on a directly connected network the closest match you can get for an address, short of the packet being addressed to you. Now then, I did slightly gloss over 1 part in the above explanation and that's the part about the router finding out the hardware address for the next hop. I just didn't want to disturb the flow with entering into that there. In some cases, this will be a hard set value like a frame relay pvc within the configuration of the router.
In some cases, you don't even need a hardware address like any point to point connection, there's only 1 possible host you could send it to , in those cases the router will just create a data link frame appropriate for the connection and it won't even need to be addressed.
- MacBook Air WiFi Problems (high latency, dropped connections) [Updated] | Jeff Geerling.
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This is why the OSI model is good. It's layered so that any layer can change and as long as it takes in information in a standard way the way the layer above wants to send it and spits out information in a standard way the way the layer below wants to receive it , then it's all good. When Frame Relay came along nothing changed with the way you had to address IP packets, all of the changes took place at the data link and physical layers. If some new type of connection comes along in the future, only the data link and physical layers will likely change.
When we go to IPv6, only the network layer should change it probably won't but that's more to do with how the layers tend to blur, but if it were truly layered that would be the case. Anyways, since I feel like doing an example here's one showing the whole process. Your computer has an address of Your default gateway is a router router a which has an address of That router is connected to the The network 2 is also an ethernet network.
Also connected to network 2 is another router router b which has the address for the interface connected to network 2 at least of Router b is also connected to network 3 Router b's interface on network 3 has the address of Now then, your computer on network 1 with an address of We'll assume that none of the info in already cached in an ARP table on any of the machines or routers a big assumption but it's mine to make!
Your computer will create an IP packet addressed to That packet will be sent to the data link layer where it needs a MAC address. Based on the subnet mask, your computer will know that the destination computer isn't on the same local network. Joined Apr 14, Messages Joined Jun 20, Messages Sabi ko ako i-PM niyo hindi ako pa mag p-PM sa inyo.
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Joined May 9, Messages HaDenz Leecher. Joined May 10, Messages Ashtra said: Joined Jan 21, Messages Nice one! Keep on helping sa mga walang MAC! You must log in or register to reply here. Friday at 3: Similar threads T.
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