Using Spanning Tree with VLANs

Using Spanning Tree
with VLANs
THE CCNP EXAM TOPICS COVERED IN THIS
CHAPTER INCLUDE THE FOLLOWING:


Describe LAN segmentation with VLANs.


Describe Spanning Tree (STP), and explain the operation of
common and per-VLAN STP implementations.


Configure Spanning Tree in both Common Spanning Tree
(CST) and per-VLAN modes.


Configure Spanning Tree parameters including: port priority,
VLAN priority, and root bridge selection.


Enable advanced Spanning Tree features such as BPDU
guard, PortFast and UplinkFast and BackboneFast.


Configure Fast EtherChannel and Gigabit EtherChannel on
inter-switch links.

Redundancy is the ability to provide an immediate backup solution
to a fault in the network that might otherwise cause a network or
component service outage. When you’re building a redundant network—
which is a network with redundant power, hardware, links, and other network-critical
components—network loops can occur. The Spanning Tree Protocol (STP) was created to overcome
the problems associated with transparent bridging at layer 2.
Unfortunately, STP is a far from optimal protocol. We can hardly blame the designers for
this—all they had to work with was a forwarding system designed to transmit broadcasts out
of every port, and the option of adding a little intelligence with Bridge Protocol Data Units
(BPDUs). So legacy STP leaves us with suboptimal forwarding paths, unused spare links, and
the possibility (probability, even) of very slow convergence after a network failure.
This chapter extends our coverage of STP by focusing on providing link redundancy by using
STP and the IEEE 802.1D algorithm used to support STP on a per-VLAN basis. The Spanning
Tree Protocol uses timers to make the network stable. You’ll also learn how to manage the different
STP timers to maximize the efficiency of your network, and how to implement specific
additions to STP to decrease convergence times