STP will block some ports in order to prevent this. At the time of the first ARP or DHCP request, the switches will start to send broadcast frames again and again because of the loops, which will cause a broadcast storm that slows down the system heavily. This topology has 3 physical loops, and if we don’t use STP, it won’t work as expected. All the connections between switches are trunks. The Layer2 access switches have redundant connections to the Layer3 core switches, and they also have some redundancy. In Room2, the PCs are part of VLAN 10 and 20, and those in Room3 are only in VLAN 30. We suppose that in Room1 there are 13-13 PCs in VLAN 10 and 30, therefore we’ll also need a hub. VLAN 10 and 20 have separate servers in them. We’re using VLANs also, namely VLAN 10, 20 and 30. We can use some Layer2 switches (I used Catalyst 2960s), some Layer3 switches (Catalyst 3560s), a hub, and some PCs and servers. Of course, it’s better to use real devices, when possible. I used Packet Tracer simulation software, which is available for all members of Cisco Networking Academy. Let’s start with the topology of the lab. In this article, I’ll present a lab scenario, along with some theory, which can help you to better understand the logic behind STP. In the CCNA exam, STP and its derivatives are an important topic. It effectively eliminates logical loops, while allowing physical loops to still exist.

Spanning Tree Protocol (or STP for short) was created to solve these kinds of problems. This design, however, has its disadvantages: on physical loops, there can be some unwanted side effects, such as broadcast storms or duplicated frames. In a switched network, redundancy can be achieved by having more switches and more connections between them. It’s the same as having more than one TV so you can watch your favorite show since if we only have one and it gets broken, we cannot watch the show.

Redundancy means using more devices and more conections than we really need. What is the solution? We can use redundancy as an example.

But technology is sometimes under the influence of Murphy’s law: “Anything that can go wrong, will go wrong.” Users expect that they can use its services anytime, anywhere. High availability is a must in any modern network.

Packet tracer labs spanning tree