Layer 2 Communication

[navneet_78]

HOw does a frame which has to reach a server on another network find out the destination server's MAC address. What is the process for MAC address lookup .

Does the Source Device has the MAC address of the destination device ( i another network) in its frame header.

[navneet_78]

Also I wanted to know during initial communication between end devices across networks what are the contents of the Layer 2 and layer 3 address?

Awaiting your reply.

[ankurbhasin]

Hi Navneet,

No the server does not have the mac address of the other server in another network.

Now what happen if a server in its network want to contact another server in another network it will request for mac address via sending a arp request and and tht arp entry will be replied by servers default gateway mac address which will be a router or layer 3 switch in most of the cases.

Now the frame will be send out from the server with its source mac adress , its source ip address and destination ip address of the other server and destination mac address of its default gateway.

One the frame reaches the router (default gateway) , router will again send a arp entry for destination ip adress of the remote server and will get a mac address of remote server and will rewrite the frame where the source mac address will be the routers mac address, source ip address of the sending server and destination mac address will be remote servers mac address and destination ip address will be remote servers ip address.

And same way the reply will come back.

So the layer 3 device will rewite the frame where the mac address is changed and incase if theer is any vlan it is rewritten.

HTH, if yes please rate the post.

Ankur

[navneet_78]

Thanx for the Reply Ankur.

Here the Destination MAC address of Host A would be that of the Router's Incoming interface or the Switch's MAC address??

Regards

Navneet

[ankurbhasin]

Hi Navneet,

The destination mac addres of HOST A will be the routers incoming interface address.

As I mentioned in my previous post routers incoming interface ip adress will be the default gateway for your host A right. So when Host A will send an arp request because HOST B is in other network router will reply to HOST A with its mac address.

So Destination MAC address of Host A would be that of the Router's Incoming interface and not the switch mac address.

HTH, if yes please rate the post.

Ankur