Router Mac Address's

[808Alaska]

Hi everyone, i just learned that each port on a router has its own mac address, which i dont understand. if someone can clear all of this up for me i would really appreciate it. What i dont understand is why each port of a router has to have its own mac address. I can see the necessity of each physical port having its own IP address but i cant see the mac address. what is it for? Wouldn't it be easier if each router had a mac address just for the router itself and not for each physical port? Or is it for trouble shooting purposes? and im pretty knowledgeable about all this networking stuff so please go into detail if you wish.
Thank you all in advance.

 

[oldskool]

It's because the MAC address operates at the Data Link Layer of the OSI model, and that is how hardware is detected on any given network when data is passed along between devices.

So the reason the router has to have seperate MAC addresses, is because each device connected to that router has IT's own MAC address, so the router will say "hhmmm, this packet (or "frame" when it is described at the Data Link Layer - Layer 2 of the OSI model - the layer that MAC addresses are dealt with), belongs to the device with XX:XX:XX:XX:XX:XX MAC address, and the routher will pass these frames to and fro via using the MAC address through that particular port only with that device.

It's like having a hall pass to use the bathroom in school, and some thug at the door lets you in and out depending on your pass, and through your own door.

 

[808Alaska]

OH ok i get it now. So the MAC addresses are used more so for the hardware detection when sending packets, and the IP address is used for network location. cool, so when layer 3 does its encapsulation of the IP address and send it to layer 2 for the mac address, its for hardware detection which makes total sense being that DHCP dynamically gives out IP addresses so it would need some kind of permanent address to make sure its sending it to the write hardware being that not every networking device has its own static IP address, lol. well thanks for clearing stuff up for me, i really appreciate it.

 

[oldskool]

To take it further, the MAC address is what most devices are concerned with initially. For example, a hub or bridge doesn't concern itself with the Layer 3 part added to the frame because it isn't designed to do that. It is a layer two (Data Link layer device). Routers, and some "intelligent switches" are Layer 3 devices, and operate at Layer 3 obviously, so they look at the layer 3 code, and read the intended IP address, the sending IP address, and other things.

It isn't sent to higher layers on any of the computers en route to the end machine because it isn't intended for them per the field located within the packet regarding destination IP address. But the machine that it IS intended for, says "hmmm, this is MY packet !," and sends it to its 4th, 5th, etc. layers. Once at the 7th layer, it is interfaced with an application such as a web browser.

 

[808Alaska]

Oh ok i c. Thanks for all the info! im planning on taking my CCNA in a little bit. thats why im so curious about this stuff. Are you CCNA certed? you sound like it. lol.

 

[oldskool]

No I'm not. But I have had 4 networking classes in college, so this stuff is pretty recently imprinted in my head.

Suggestion: Before you take any cert tests, you really need to understand this stuff at a much more advanced level than you understand it right now. And I mean no offense to you, but this is a really basic networking concept compared to what you will see on the CCNA testing, so take your time and really study up on it to make it worthwhile when you do take the CCNA.

 

[808Alaska]

oh yeah definitely. Im currently in my first cisco networking class and i have 3 more to take before im gonna even get close to signing up for the exam, i just hope i can take it soon though before they put some IPv6 in thier, lol. well thanks for all your help i really appreciate it.

 

[oldskool]

No problem, mate. Any time.