What will You Gain from this guide?
After this guide you should be able to configure a functional network with two routers. We will be using static routes in this guide to route the traffic from one side of the network to the other. In this guide we will be building the topology above step-by-step so don’t worry if you aren’t familiar with the necessary commands or with Packet Tracer.
What you need?
- A PC
- Cisco Packet Tracer
- Some basic knowledge about networks and how they work
- Knowledge of OSI Model
- Basic understanding about subnets
packet tracer preferences
This section is completely optional but recommended. I will quickly be going over my preference settings for Packet Tracer. Load up the program and do the following:
- On the top toolbar click on the word Options
- From there click on preferences
- Match your settings to the ones below and check off any others you might want to try out
setting up the topology
Now we are going to add the routers, switches, PCs, and the correct wires into Packet Tracer.
- On the lower left hand side make sure that network devices is selected (this is the default selection). Below this, make sure that Routers is also selected.
2. Locate the 2911 Router and drag and drop it into the upper left corner (similar to the first picture in the article). Do the same thing but this time place the router to the right of the other one.
3. To the right of Routers is Switches, click on that and drag and drop two 2950T switches into your topology, one under each router.
4. This time click on ‘End Devices’ next to ‘Network Devices’ and drag and drop a PC or Laptop underneath each switch.
Connecting the devices
Your topology should look similar to the one above but, it is still missing the connections between each device. When connecting two devices on the same layer of the OSI Model, it requires a crossover cable. In this case, both of the routers need to be connected with a crossover cable because they are layer 3 devices.
- Start by clicking on the lightning bolt symbol which is the Connections tab
- Click on the solid black line (this is the straight-through cable symbol) and then click on one of your routers. Connect the cable to GigabitEthernet0/1 or g0/1 for short. Connect the other end of the cable to the switch below its g0/1 port. Do the same thing with the other router as well.
- When connecting routers to themselves or switches it is always advised to connect them by the fastest available port. Never connect a gigabit port to a FastEthernet port, it’s a waste of resources and will most likely get you laughed at by others.
- Now grab another straight-through cable and connect it to one your switch’s FastEthernet0/1 or f0/1 port. Connect the other end of the cable to the PC below it in the only available Ethernet port. Do the same thing for the other switch and PC
- This time click on the dotted line cable, not the zigzag line, and connect it to one of the routers’ g0/0 port. The dotted line is the symbol for a crossover cable. Connect the other end to the other router’s g0/0 port.
Configuring a switch
At this point, your topology should look similar to the one at the top of this post. We will be using a Class C IP address for the two separate networks and a Class A address for the point-to-point connection between the routers. For this network to work, we actually do not need to configure the switches. We will get more into switches and VLANS in future tutorials but for now we are just going to configure the routers.
configuring a router
Before this point, I told you to pick and choose which side you wanted to setup and wire first. Now it is important that you only work on the specific side that I tell you to work on. Let’s start with the left most router. We will be using Cisco’s IOS Command Line Interface to configure the routers. This is just the operating system installed on these devices. If at any point you are not sure what to enter after a command you can simply type in a ? and Cisco IOS will tell you what you need to enter.
- Left-click the top left router one time. At this point, we don’t need to worry about any of the modules or config settings. Click on the ‘CLI‘ tab and then press enter.
- This is the User EXEC Mode within Cisco’s IOS. Not a whole lot can be done from here, I have personally never done anything at this privilege level except type in enable or en for short.
- At the bottom of the window you should see:
- After the > type in the following command:
Router>en (Hit the tab key to auto-fill or just press enter)
- At this point you should see:
- This is Privileged EXEC Mode, it is mainly used for troubleshooting the device’s configuration and connection with other devices. We will return back to this after both routers are configured.
- Enter the following command to enter Global Configuration Mode. This is where we will actually configure the router.
- Short hand for this command is just conf t
naming your router, setting a password, and adding a banner
- Now let’s give our router a name. Because we are configuring our left router, let’s keep it simple and name it LeftRTR.
- Now we will set a password on our router. In this case we will just be using cisco as our password to keep things simple. The password screen will appear after you type in en or enable to get into the router. You will see why after examining the following command:
- Only enter one of the following commands
LeftRTR(Config)#enable secret cisco (secret = encrpyted)
LeftRTR(Config)#enable password cisco (password = unencrypted)
- If you chose to enter password instead of secret, your device is obviously less secure. To fix this and encrypt all passwords on the router (past, present, and future) type the following command:
- Remember that you can tab each word in a command to auto populate the rest of the command.
- We can also add a banner that will appear the next time you login to the router. This is where a business or person would set a disclaimer or message warning anyone who should not be there to get out.
LeftRTR(config)#banner motd “Enter Your Message Here”
saving your work
- Now we can save all of our work a couple different ways. The short-hand for the first one is wr and the second is copy run start.
- It is important to note that you can save at any point after Privileged Exec Mode but, if you are in Global Config Mode you need to add do in front of your commands.
LeftRTR(config)#do copy running-config startup-config
Destination filename [startup-config]? *Press Enter*
- Now to exit global config mode and save the other way. If you already saved it is not necessary to save again but it is good information to know. Remember, you only need to save with one of the above methods, I personally use do wr or simply wr.
LeftRTR#copy run start
checking your running-configuration
- Now to check our running-configuration (running does not always mean saved so remember to save often):
You should recognize everything highlighted as commands that we previously entered. The only difference is that after enable secret we can see the encrypted string for cisco.
- Hit space to skip an entire page or enter to skip a line.
- Underneath the interfaces you will find your banner and whatever phrase you entered.
Configuring the interfaces
labeling the interfaces
This section will teach you how to setup the interfaces on the router so that it can communicate with the other router and the switch. As a reminder, the left most network is using the 192.168.1.0/24 IP address range.
- Start by assigning IP addresses to each interface on both routers and the PCs
- Click on the highlighted icon and then click on a blank space to the left of the left router. This is how to add notes to your topology.
- On the topology, assign the following IP addresses to the left router:
- Left PC:
- Right Router:
- Right PC:
ASSIGNING THE IP ADDRESSES
- Open up your left router
- Enter Global Config Mode
- We are going to configure the left network first, not the point-to-point network. Do so by accessing the g0/1 port.
- Assign this port the correct ip address of 192.168.1.1 as well as its subnet mask. The subnet for a /24 network is 255.255.255.0
LeftRTR(config-if)#ip address 192.168.1.1 255.255.255.0
- The ports on the router are down by default so we need to bring the port up after giving it an IP.
- Exit the interface and bring up interface g0/0
- Assign the correct IP and bring the port up
- The subnet mask for a /30 network is 255.255.255.252
- Save your work! Never forget this step. If this was an actual router and it was powered off without saving, you would have to reconfigure everything up to the last save.
- Congratulations! You have successfully configured a router and setup your own network topology on Cisco Packet Tracer.
- We can’t test our point-to-point network because we haven’t configured the other router yet. Remember that a router’s ports are defaulted to down so the link on g0/0 should still be red; however, you should see a green link under your left router’s g0/1 port.
testing your configuration
There a couple ways to test your configuration, in this guide I will be going over just one of those methods. This method is to ping your router from your PC.
- Click on your left PC
- Select the Desktop tab
- Now click on IP Configuration (Not the only method to assign the PC an IP but it is the easiest)
- In the blank next to IP Address enter the PC’s IP: 192.168.1.2
- Click the blank next to Subnet Mask and it should default to 255.255.255.0. If not, enter this in manually
- Your default gateway is the IP for the router and port that the PC is directly connected to. In this case it is the IP for the left router’s g0/1 port 192.168.1.1
- Hit the ‘X’ to the right on the blue bar
- Select the Command Prompt
- type in ‘ipconfig‘
- Verify the highlighted fields
- Type in ping 192.168.1.1
If your ping looks like the picture above congratulations, you have a fully functional network on the left side of your topology. If you receive an error such as destination host unreachable or request timed out, go back and take a look at your configuration. Remember to use the show running-config or show run command to check your configuration.
Now that you have one side of your network up and running, I want you to configure your right router, your PC, and test the network.
- Name your router
- Secure the router with a password and banner
- Configure both interfaces
- Save your work
- Check your work (Show run)
- Set up a static IP on your right PC
- Test your connection(ipconfig and ping)
Things to remember:
- A /24 network and a /30 network have different subnets
- Save and save often
- Always check your work
- Router ports are down by default
- You will only be able to ping from your PC to the router it is directly connected to (Left PC can not ping right router or right PC). This will be the next section of the guide)
setting up static routes
What happens without them?
Now that both sides of the network are setup I want you to try and ping one of your PC’s with the other PC. What error did you get? It should looks something like the image below:
This error is because the right PC and right router do not know about the left side of the network. The PC sends all of its traffic to the default gateway. The router receives the traffic but only knows about the two networks directly connected to it. That is the 10.0.0.0/30 network and the 192.168.2.0/24 network. The router doesn’t know where to send the packet destined for the 192.168.1.0/24 network because it doesn’t know about that network. The router then drops the packet and it does not reach its destination. This is why we get the Destination host unreachable error.
How to configure routes
Static routes are configured within the Global Config Mode of a router. For this example, we will be looking at the left router again.The left router does not know about the right network because routers break up broadcast domains. The right router stops the broadcasts from the right network before they make it to the left router. If we want to talk to the right network, we first have to tell the left router about the other network.
- We do this by entering a single command on each router
- We type this command once for each network that a router can not reach
- The command for the left router should look like this:
Example: LeftRTR(config)#ip route “IP for the network” “subnet” “port that is closest to the other network”
LeftRTR(config)#ip route 192.168.2.0 255.255.255.0 g0/0
Traffic from the left network must exit through port g0/0 in order to reach the right network, this is why we put the exit port at the end of the command. Now save you work and exit the router. Open up your right router and type in the necessary command for this router to reach the left network. What did you come up with? It should look something like:
RightRTR(config)#ip route 192.168.1.0 255.255.255.0 g0/0
testing the network
At this point, your network should be fully functional. click on of your PCs and ping away. Try to ping every device with an IP and they should all work if everything is configured correctly. If you don’t get a reply immediately that’s okay. The first ping or two normally don’t get a reply when you first setup routes and send traffic.
This has been quite a long journey but hopefully you were able to successfully setup your first network using Cisco Packet Tracer. If you have any trouble with a certain topic or can’t troubleshoot your network, be sure to drop a comment and I will try to help you out. If you have any suggestions or updates for this post please feel free to comment or contact me via email.