If you are taking a CCNA course, you will spend a lot of time inside Cisco Packet Tracer. It is a powerful tool, but it is also completely unforgiving. If you make one tiny mistake, your network will fail to ping, and you will be left staring at a screen of red dots.
After helping dozens of students pass their networking labs, here are the top 5 mistakes we see every single week (and how to fix them).
1. Forgetting to "No Shut" the Interface
By default, every physical interface on a Cisco router is administratively down. If you assign an IP address but forget to turn the port on, nothing will work.
Router(config)# interface GigabitEthernet0/0 Router(config-if)# ip address 192.168.1.1 255.255.255.0 Router(config-if)# no shutdown
2. The Default Gateway is Missing
You configured your switch and your router, but you forgot to tell your PC what the default gateway is. In Packet Tracer, click on the PC > Desktop > IP Configuration, and make sure the Default Gateway is set to the router's IP address.
3. Trunk Ports vs. Access Ports
If you are setting up VLANs, you have to tell the switch which ports connect to other switches. A port connected to a PC should be an Access port. A port connected to another switch or router should be a Trunk port.
Switch(config)# interface FastEthernet0/1 Switch(config-if)# switchport mode trunk
4. Routing Loops
If you are configuring OSPF or EIGRP, and your network is slow or dropping packets, you might have a routing loop. Always double-check your network addresses and the wildcard masks in your routing commands.
5. Forgetting to Save the Configuration
You did all the work, the network pings perfectly, and then you close the application. When you open it again, everything is gone. Always run copy running-config startup-config on every single device before you close the lab.
Still Stuck on Your Cisco Lab?
Packet Tracer labs are great for learning, but they can be incredibly frustrating when you are on a deadline. If you are stuck on a VLAN configuration or a routing protocol that won't converge, we can help.
We offer live 1-on-1 Cisco tutoring. You share your screen in Packet Tracer, and we walk through the CLI together until it works. No generic answers — we teach you the actual commands.
💬 Get Cisco Tutoring on WhatsApp