Many devices will strip off the L2 header before 元 processing, but even if this isn't always the case it doesn't obscure the meaning of the rest of the message. The L2 header doesn't change the content that becomes the L2 payload, it is simply pre-pended or added before the 元 header. The 元 header is not "hidden" by the L2 header. IP wouldn't care or be bothered by the change.Īnd how do routers look up the IP adress, if it is hidden beneath the data link layer? I don't really get it. IP is designed to work without concern for the underlying protocol, so you could replace Ethernet with something else (like Token Ring or Frame Relay) or you could create your own L2 protocol if you wanted. This is one of the reasons that NAT exists.įurther, Ethernet is only one L2 protocol. They must be unique on the local network, but they can be re-used. No, IP address are not necessarily unique.
Why is it even necessary to add the MAC address? The IP address will already uniquely identify it, won't it? The router will adjust the L2 information before it passes the traffic on to the next 元 device. Generally this is the default gateway for most devices, and as you point out, your computer already has the information for your router in your ARP table.
Use mac address for chromecast on router how to#
Since the MAC address is only used within the same L2 network, when you are sending traffic to a different 元 network, all it needs to know is that is on a different 元 network and how to get to that 元 network. Your computer doesn't, nor does it need to do so. Well, but how does it find out it's [MAC address needed for 802.11 data link layer? But what MAC address will be written inside that field between my router and the destination router? I know that my machine contains an ARP table which contains the MAC address of my router. I learned that the 802.11 header as well as the 802.3 header contains a field for Destination MAC addresses. Why is it even necessary to add the MAC address? The IP address will already uniquely identify it, won't it? And how do routers look up the IP address, if it is hidden beneath the data link layer? Well, but how does it find out it's MAC address needed for 802.11 data link layer? No machine on my local network knows it. DNS will find out that the IP address of is 93.184.216.34.
The ICMP echo doesn't contain any application layer or transport layer. Let's say I send a packet to someone not on my local network, e.g. static fixed IP addresses assigned by DHCP servers or for Wireless access points. I know that MAC addresses are used in networks for several things, e.g.
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