Doubt in Routing

Atharva Bet

Hello,
I had a doubt in routing. Everyone says that when a particular router receives a frame, it strips off the Layer 2 Header & Trailer i.e it decapsulates Layer 3 (IP) information, analyses it, or processes it, and then makes a new Layer 2 header. Now the new layer 2 Header should probably have the Mac Address of the next router which is in the way that will receive the frame. And, this process shall go on unless the frame reaches that router in whose LAN that particular Host/Server is present. Kindly correct me if I'm wrong till here.

Now I have 2 doubts actually:

1) What does that router actually analyze/process on the IP information when it strips off the Layer 2 header and trailer? How does that IP information help that router in routing? How does the router know that the next router that it'll send the frame is the right router to send? Does IP information help in all of that?

2) How does the router know the Mac Address of the next router in the line that it'll forward the frame to? Do they use ARP requests for that?

Also, am I digging too deep in contrast to what information I should technically have while preparing for CompTIA Network + considering it an entry-level certification? Is it really necessary to know soo much? Actually, I'm quite curious all the time and I love asking questions. Sometimes I really ask silly doubts too, Sorry for that :)

Thanks.

Ronnie Wong

@Atharva-Bet said in Doubt in Routing:

Hello,
I had a doubt in routing. Everyone says that when a particular router receives a frame, it strips off the Layer 2 Header & Trailer i.e it decapsulates Layer 3 (IP) information, analyses it, or processes it, and then makes a new Layer 2 header. Now the new layer 2 Header should probably have the Mac Address of the next router which is in the way that will receive the frame. And, this process shall go on unless the frame reaches that router in whose LAN that particular Host/Server is present. Kindly correct me if I'm wrong till here.

Now I have 2 doubts actually:

1) What does that router actually analyze/process on the IP information when it strips off the Layer 2 header and trailer? How does that IP information help that router in routing? How does the router know that the next router that it'll send the frame is the right router to send? Does IP information help in all of that?

As data travels along the path it compare the header information to it's down in certain fields. e.g. When a router receives a frame. It will look at the destination MAC address. Does that mac address match the mac on that NIC? If not, the frame is dropped; if it does then the frame is processed and moves up to the Network Layer. The the same thing will happen. It will check the destination IP address in the packet and see if it compares with the IP address configured on the device. If it matches, the packet has reached it's final destination. If it doesn't match, a router will look in the routing table to see if there's a route that matches and forwards it out of the interface towards that network.

2) How does the router know the Mac Address of the next router in the line that it'll forward the frame to? Do they use ARP requests for that?

This all routers are connected in a point-to-point or multipoint topology. That means routers will send ARP requests to its neighbors.

Also, am I digging too deep in contrast to what information I should technically have while preparing for CompTIA Network + considering it an entry-level certification? Is it really necessary to know soo much? Actually, I'm quite curious all the time and I love asking questions. Sometimes I really ask silly doubts too, Sorry for that :)

Thanks.