Summary (3.4)
Class Activity 3.4.1.1: Documentation Tree
Refer to Scaling Networks v6 Labs & Study Guide and the online course to complete this activity.
The employees in your building are having difficulty accessing a web server on the network. You look for the network documentation that the previous network engineer used before he transitioned to a new job; however, you cannot find any network documentation whatsoever.
Therefore, you decide to create your own network record-keeping system. You decide to start at the access layer of your network hierarchy. This is where redundant switches are located, as well as the company servers, printers, and local hosts.
You create a matrix to record your documentation and include access layer switches on the list. You also decide to document switch names, ports in use, cabling connections, root ports, designated ports, and alternate ports.
Problems that can result from a redundant Layer 2 network include broadcast storms, MAC database instability, and duplicate unicast frames. STP is a Layer 2 protocol, which ensures that there is only one logical path between all destinations on the network by intentionally blocking redundant paths that could cause a loop.
STP sends BPDU frames for communication between switches. One switch is elected as the root bridge for each instance of spanning tree. An administrator can control this election by changing the bridge priority. Root bridges can be configured to enable spanning-tree load balancing by a VLAN or by a group of VLANs, depending on the spanning-tree protocol used. STP then assigns a port role to each participating port, using a path cost. The root path cost is equal to the sum of all the port costs along the path to the root bridge. A port cost is automatically assigned to each port; however, it can also be manually configured. Paths with the lowest cost become preferred, and all other redundant paths are blocked.
PVST+ is the default configuration of IEEE 802.1D on Cisco switches. It runs one instance of STP for each VLAN. A newer, faster-converging spanning-tree protocol, RSTP, can be implemented on Cisco switches on a per-VLAN basis in the form of Rapid PVST+. Multiple Spanning Tree (MST) is the Cisco implementation of Multiple Spanning Tree Protocol (MSTP), where one instance of spanning tree runs for a defined group of VLANs. Features such as PortFast and BPDU guard ensure that hosts in the switched environment are provided immediate access to the network without interfering with spanning-tree operation.
Switch stacking allows connection of up to nine Catalyst 3750 switches to be configured and presented to the network as a single entity. STP views the switch stack as a single switch. This additional benefit helps ensure the IEEE recommended maximum diameter of seven switches.