Hi, at first I would like to thanks to you, because of your continuing interest in computer networking. Today we will do network monitor task by examining a packet traveling. We’ll see how the packets travel through which path. We’ll use a topology in which the packet will travel to another path and packet will not travel to another path.
Network monitor for router default route system of network model
We’ll do all this tasks using the powerful network simulator named cisco packet tracer. This simulation tool is provided by cisco. It is recommended to use cisco packet tracer latest versions. If you don’t have the cisco packet tracer latest version, you can download it from this whilenetworking.com blog. So it can say that, you have downloaded and installed the latest cisco packet tracer. So lets start.
For this topology we’ll use:
Three router and three PC. And draw the topology and implement the IP address in each of the device. Just like the following picture:
If you have problem of drawing the scenario in the packet tracer, then don’t worry, I’ll provide it to you at the end of this post. This packet tracer file is actually provided by cisco for the better knowledge of the students. Generally IP packets between networks are forwarded by routers. And every router has routing table, this routing table can helps a packet to reach its destination by examining the next hop for the destination. If router find that the packet arrived has a destination address, which match its routing table address for the next hope address, then the packet is forwarded by the router to that address. Sometimes there is no matching of the packet about its destination address in the routing table, but still matches the default route with the address of routing table, then the router forward the packet to the default route. If there is no match with the routing table, then the packet is discarded by the router.
So now come to our topology, here is three LAN is indicated.
PC_A has the LAN address: 10.1.1.0/24
PC_B has the LAN address: 10.1.2.0/24
PC_C has the LAN address: 10.1.3.0/24
Router0 has the address of 10.1.2.0/24
Router2 has the route to 10.1.1.0/24
Router0 has no route to 10.1.3.0/24
but has a default route out interface S0/0/1 (toward Router1).
Router1 has no route to 10.1.1.0/24 and no default route. So a ping from PC_A will reach PC_C but the reply will be dropped by Router1.
So lets monitor network in the simulation mode. We’ll try to trace the packet. At first we’ll try the tracing of network monitor between the PC_A and PC_B.
Step a: Enter the simulation mode, which stays at the right bottom of the packet tracer.
Step b: Now place a packet from PC_A and then place it to PC_B.
Step c: Click the auto capture/play
Here you’ll see and can able to do the task of network monitor. Packet will go to the PC_B from PC_A because there is a routing address is located at the router. To see the routing table, click the Inspect tool (magnifying icon) and after that click the router0 or router2. You can be able to see the routing table. If you have a close look at the routing table, you can see that, the destination address is located in the router.
Now come to the packet travelling of PC_A to PC_C. Just try to send a message from PC_A to PC_C. What you’ve seen in the event window? Most probably you’ll see a “Failed” notification. It is because the destination address is not properly assigned. Now in the simulation mode also try to send a packet from PC_A to PC_C. Click the Auto capture/Play. Now monitor network clearly between them. You can see that, the packet travelling from PC_A to PC_C, because Router0 has a default static route. Also for that, the destination network is connected directly with the Router1. The packet which travel to PC_C can’t send a confirmation request to the PC_A because these routes don’t in both directions. If you look at the event window you can see that, the packet which travels to PC_C, can’t travel back to PC_A.
You can download the packet tracer file used here. I’ve uploaded it to google drive. Lets download this:
If you want you can enjoy this video, i’ve made this video for you:
So that’s all for this post. Hope that you’ve realized this packet traveling. And also hope that you can able to monitor network. If you have any kinds of opinion or question please feel free to comment. 🙂