Content

| Overview

Of all the protocols that network engineers spend time learning about and planning for, the one that is probably overlooked the most is Spanning-Tree Protocol (STP). As routers became popular in the early 1990s, STP faded into the background as a “less-important protocol that just worked". However, with switching technology now in the forefront, STP has once again earned its place as an important consideration in network design.

A poorly planned initial implementation of STP can mean that an inordinate proportion of the configuration, troubleshooting, and maintenance effort on a campus network becomes devoted to STP. This module explains the mechanics of Spanning-Tree Protocol, detailing its loop-prevention function in switched networks. Understanding these mechanics enables a proactive rather than reactive approach to configuring spanning tree on the target switched network.

STP is one of the most technical subjects in LAN switching. The challenge of understanding STP is similar to that of understanding the underlying operation of OSPF or EIGRP in a campus network (timers, packet types, algorithms, and so on). It is essential to gain this understanding. STP serves as a fundamental logical building block in every campus network and it plays a key role in network design and implementation.

This module discusses Layer 2 techniques and technologies designed to optimize network reliability, resiliency, and redundancy within a campus network. In particular, this module explores scaling issues with STP as they pertain to virtual LANs (VLANs) and VLAN Trunking Protocol (VTP).