switch use MAC?

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Hi,

Why is it that TCP/IP network switches still use MAC addresses, i realsise that DHCP is an issue but can the switch not update its table to reflect that when a ARP is sent.

And why do packets still have to use MAC addresses also.

Regards

Classic.

 

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depends on what context your meaning.

When data is sent across a network how does it get to where it needs to go? how does the computer recieving that data know its from the computer that sent it? Answer MAC addressing. No two MAC addresses are the same so this provides excellent piece of mind for the sender and the reciever.

 

How would the host obtain it's DHCP lease without using MAC addressing?

As far as I understand it, ethernet frames use MAC addresses, not packets. Frames, as the name implies, frame packets so they can be delivered locally. Therefore, packets do not use MAC addresses.
I could be wrong on that though. Hopefully someone more experienced can confirm/deny my understanding of it.

 

Hi,

You are right about the Ethernet Frames with the encapsulation of IP packets, which is what i meant, IP packets using Ethernet frames. (MAC addresses)...first time at forums.

I guess I just wondered why when Data is sent from a host, and all IP addressing is established that the need to use MAC addresses in every Frame is still relevant. Say that all hosts used static IP addresses for example, I'm guessing that you could say some of the Layer 2 information can be omitted.


Classic.

 

Yep frames use MAC adresses.
ARP is used to identify a networks host when only the IP is known.
When a packet arrives at a router, the router examines the IP address put there by the IP protocol layer on the originating computer. The router checks it's routing table. If the network containing the IP address is found, the packet is sent to that network. If the network containing the IP address is not found, then the router sends the packet on a default route, usually up the backbone

 

A Network card operate on Layer 2 of the OSI model, whereas IP operates on layer 3, so network devices cannot essentially read an IP address.
Basically every network card has a mac address (which is a level 2 address), its kind of like a serial number, all are unique, and for instance anything to communicate on a local network the devices have to communicate with either a hub or a switch (or directly).

For info A hub broadcasts all traffic on all ports, whereas a switch is clever, it keeps a switching table that when it receives a packet from a network device it keeps a record of that mac address and which port is uses, so it can send the traffic to the correct port in future, thus saving bandwidth.

Also when two computers communicate they keep a list of IP addresses and mac addresses in the arp, you can type in arp -a in a command prompt to see this.

So basically thats the reason and some of its application, hope thats cleared things up a little.

 

Ethernet works at layer 1 and 2. This is how the data (the actual bits of data being sent) gets to it's destination. IP works at layer 3, which does not have its own way to encode this data onto the wire.