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Arista Warrior by Gary A. Donahue

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Chapter 13. Spanning Tree Protocol

Spanning tree protocol (STP) is very important in layer-2 networks, and its impact should be clearly understood when designing or even troubleshooting a network. If you’ve been around Cisco gear for the majority of your networking life, you’ve probably used Per-VLAN Spanning Tree (PVST) or Rapid-PVST (RPVST). In this chapter, I’m going to primarily cover a form of STP that is becoming more common in large data centers: Multiple Spanning Tree (MST).

Data center networks have very different requirements than enterprise networks do. For example, few of the enterprise networking professionals I meet know that many switches have spanning tree limitations. I worked for a client that had Cisco 3750s in the core of a small data center. Things seemed to work alright until they added the 257th VLAN, and that’s when they learned that Cisco 3750s only support STP up to 256 VLANs. Bummer.

I was brought in to help solve the problem, and after my recommendation of, “Buy data center class chassis switches” was ignored, I looked for other options. That’s when I learned about MST.

Arista switches can run a variety of STP types. You can change the type using the spanning-tree mode mode-type command:

SW1(config)#spanning-tree mode ?
  mstp        Multiple spanning tree protocol
  none        Disable spanning tree
  rapid-pvst  Per VLAN rapid spanning tree protocol
  rstp        Rapid spanning tree protocol

Since I’ve covered spanning tree and rapid-PVST in Network Warrior, I’m going to focus mostly ...

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