200 301 ccna study material

200 301 ccna study material.STP has been around for more than 30 years, first coming into use even before the IEEE's development work based on the Ethernet standard proposed by Xerox and other distributors.The IEEE first incorporated the STP standard into IEEE 802.1D back in the 1980s.To this day, Cisco switches continue to use STP.Except for a modification to the default overhead value Except for modifications to the default overhead values, the description of STP in this chapter so far is not much different from the original STP from years ago.Despite this long and surprising lifespan, STP has undergone several major and minor changes over the decades. For example, Cisco has added some proprietary features to improve STP performance. In some ways, the IEEE incorporated or built upon these improvements in subsequent IEEE standards, either as revisions to the 802.1D standard or as add-on standards. It was originally defined in IEEE 802.lw.The last of the three main sections in this chapter briefly discusses the basics of optional features that go beyond the 802.1DSTP concept, including Ethernet channels, fast ports, and BPDU protection.1. Ethernet ChannelsOne of the best ways to reduce STP convergence time is to avoid full convergence. Ethernet Channel provides a way to prevent STP from initiating convergence when just one individual port or cable fails.Between the same pair of switches, multiple (up to 8) parallel lines with equal rates can be combined and bound into a single Ethernet channel. The switch treats the Ethernet channel as a single interface for the frame forwarding process, and the same is true for STP. Therefore, if one link fails, but at least one link state is available (up), STP convergence will not occur at that time. For example, in a network of three common switches, there are two Gigabit Ethernet connections between each pair of switches, as shown in Figure 1-10.Each pair of Ethernet links is configured as an Ethernet channel, and STP treats each Ethernet channel as a single link. That is, both links connected to the same switch must fail in order for the switch to trigger STP convergence. In the absence of an Ethernet channel, if there are multiple parallel links between two switches, STP leaves only one link and blocks all the remaining links. If an Ethernet channel is applied, all parallel link states are available (up) and can work simultaneously, which both reduces the number of times STP must converge and increases the availability of the network.Archie.20 Chapter 1 Defining the Spanning Tree ProtocolWhen a switch decides to perform forwarding and send a frame out of an Ethernet channel, the switch must theoretically take another step:Which physical interface is it going to send it out of? Switches have load-balancing logic that enables it to select an interface for each frame, with the goal of spreading the data transfer load among all available links within that channel. The result is that LAN designs that use Ethernet channels make more scientific use of the bandwidth between switches while reducing the number of times STP must converge.