Chapter 12

Redundant Switched Technologies

The following topics are covered in this chapter:

  • Building a Redundant Switched Topology
  • Recognizing Issues Associated with a Redundant Switched Topology
  • Resolving Redundant Switched Issues with STP
  • Describing 802.1w RSTP
  • Describing 802.1s MSTP
  • Describing LAN Port Channels
  • Verifying LAN Port Channels

Long ago, a company called Digital Equipment Corporation (DEC) was purchased and renamed Compaq. But 30 years before that happened, DEC created the original version of Spanning Tree Protocol, or STP. The IEEE later created its own version of STP called 802.1D. Cisco has moved toward another industry standard in its newer switches called 802.1w, which NX-OS runs by default. It actually can’t even run the older 802.1d legacy protocols, though the new 802.1w RSTP is backward compatible.

We’ll explore both the old and new versions of STP in this chapter, but first, I’d like to define some important STP basics.

Routing protocols like RIP and OSPF have processes for preventing network loops from occurring at the Network layer, but if you have redundant physical links between your switches, these protocols won’t do a thing to stop loops from occurring at the Data Link layer. That’s exactly why Spanning Tree Protocol (STP) was developed—to put an end to loop issues in a layer 2 switched network. It’s also why we’ll be thoroughly exploring the key features of this vital protocol as well as how it works within a switched network in this chapter. ...

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