ccna with python

ccna with python.13.2.1 Bridge Protocol Data UnitsFor STP to function, switches must share information about themselves and their connections. They share Bridge Protocol Data Units (BPDUs), which are sent out as multicast frames and are only sent to the Layer 2 switch or bridge that is listening. The switch uses the BPDUs to learn the topology of the network-which switches it is connected to-and to determine if there are Layer 2 loops based on the topology.If a loop is found, the switch will logically disable one or more ports to ensure that there is no loop. Note that the switch does not shut down the port, but simply leaves the port in a special disabled state for user traffic, as discussed in the "Port State" section later in this chapter. By disabling a port, only one path is available between any two devices in the Layer 2 network. If there is a change in the Layer 2 network, such as a link or switch failure, or a new link or switch is added, the switch will share this information, causing the STP algorithm to re-execute, creating a new topology with no loops.BPDUs are sent at an interval of 2 seconds by default, which helps increase the speed of convergence. In the networking world, convergence refers to the time it takes to respond to changes and get the network back to normal. The shorter the time it takes to find and fix a problem, the faster the network will return to normal. By setting the BPDU announcement interval to 2 seconds, information about changes can be shared quickly with all other switches in the network, thereby reducing network outages.BPDUs contain a lot of information that helps switches determine the topology and the loops in it. For example, each bridge has a unique identifier, the bridge ID (switch ID), which usually consists of the switch's priority and MAC address. When a switch advertises a BPDU, it includes its own switch ID in it, letting the receiving switch know which switch it received the topology information from. The next few subsections describe the steps to perform STP in a Layer 2 network.Most bridges and switches use IEEE protocol 802.Id to eliminate loops at IOS Reference Model Layer 2. BPDUs are used toshared information, and they are sent as multicast with a 2-second interval.BPDUs contain the switch ID,which consists of the priority value andThe BPDU contains the switch ID, which consists of the priority value and the MAC address of the switch.13.2.2 Root SwitchThe term Spanning Tree Protocol refers to the process of finding and eliminating loops in a Layer 2 network. the STP algorithm eliminates Layer 3 loops in a similar manner to link-state routing protocols such as Open Shortest Path First (OSPF), but eliminates Layer 2 loops (link-state routing protocols are discussed in Chapters 14 and 19)