In the previous post, we learned about L2 (Ethernet) switching. This post is about L3 (IP) routing. This time, we will look into IP routing illustrated in the right figure below.
Again, please take a close look at the network configuration above. In the figure, MAC/IP address values are as follows:
Server/Router | Port | MAC Address | IP Address | |
SVR1 | lan1 | m1 |
1.1.1.10 |
|
SVR3 | lan2 | m3 | 2.1.1.30 | |
R1
|
ge1/1 ge2/1 |
a1 a2 |
1.1.1.1 2.1.1.1 |
IP Routing
1. SVR1 sends ARP Request
Header | Fields | |
Ethernet Header
|
* Destination MAC = FF:FF:FF:FF:FF:FF (broadcasting, so sending to all nods in the same LAN) |
|
ARP Header
|
* Sender MAC = m1, the MAC address of the sender (SVR1) |
2. R1 responds with ARP Reply
Header | Fields | |
Ethernet Header
|
* Destination MAC = m1, the MAC address of SVR1 to which ARP reply is to be delivered |
|
ARP Header
|
* Sender MAC = a1, the MAC address of the sender (R1) |
3. SVR1 sends IP Packet to R1
Header | Fields | |
Ethernet Header
|
* Destination MAC = a1, the MAC address of the receiver (R1) |
|
IP Header
|
* Destination IP = 2.1.1.30, the IP address of the receiver (SVR3) |
4. R1 sends ARP Request
Header | Fields | |
Ethernet Header
|
* Destination MAC = FF:FF:FF:FF:FF:FF (broadcasting: reaching all nodes in the same LAN) |
|
ARP Header
|
* Sender MAC = a2, the MAC address of the sender (R1) |
5. SVR3 responds with ARP Reply
Header | Fields | |
Ethernet Header
|
* Destination MAC = a2, the MAC address of R1 to which ARP reply is to be delivered |
|
ARP Header
|
* Sender MAC = m3, the MAC address of the sender (SVR3) |
6. R1 sends IP Packet to SVR3
Header | Fields | |
Ethernet Header
|
* Destination MAC = m3, the MAC address of receiver (SVR3) |
|
IP Header
|
* Destination IP = 2.1.1.30, the IP address of the receiver (SVR3) |
Summary
All clients/servers (to be referred to as servers below) are connected to other servers through switche(es) and router(s).
|
netmanias! Such a pretty great source to learn about how computer network works. I'm doing bachelor and surprisingly this is the subject which I'm studying this semester. This will definitely help me out in final semester project.
Wow!!. Such a brilliant explanation.
can u pls explain why the Router R1 does not learn the mac of the server 1 and update in the ARP table , but only learns the mac of server 2 in the ARP table ? I.e when S1 sends packet to R1 , the arp table is still empty ( compared to switches which learn both the mac of router and servers)