How to Diagnose Switching Loop with Ax3soft Unicorn

Unicorn tutorials

What is Switching Loop?

A Switching loop or bridge loop occurs in computer networks when there is more than one Layer 2 (OSI model) path between two endpoints (e.g. multiple connections between two network switches or two ports on the same switch connected to each other). The loop creates broadcast storms as broadcasts and multicasts are forwarded by switches out every port, the switch or switches will repeatedly rebroadcast the broadcast messages flooding the network. Since the Layer 2 header does not support a time to live (TTL) value, if a frame is sent into a looped topology, it can loop forever.

A physical topology that contains switching or bridge loops is attractive for redundancy reasons, yet a switched network must not have loops. The solution is to allow physical loops, but create a loop-free logical topology using the spanning tree protocol (STP) on the network switches.

Diagnose Switching Loop

Step1: To diagnose switching loop, let’s launch Unicorn and start a new project. The loop creates broadcast storms, so it is a primary choice to view the Summary tab.

Figure 1: View  broadcast traffic in the  Summary tab

Step2: A network loop in the LAN can bring down your whole network. Many computer in the LAN can not connect target host, so they will send many ARP request packets.

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