ccna without degree

ccna without degree.Path OverheadPath overhead is calculated using the root switch as the reference point, which is effectively the cumulative port overhead from the root switch to the other switches in the topology. When the root switch advertises BPDUs outbound from its interface, the default path overhead in the BPDU frame is 0. The connected switch receives the BPDU and adds that path overhead to the overhead of its inbound port. If the port is a Fast Ethernet port, the path overhead will be calculated like this: 0 (path overhead of the root switch) + 19 (port overhead of the current switch) = 19. The switch advertises BPDUs to other switches, including the latest path overhead in them. As the BPDUs propagate further and further from the root switch, the accumulated path overhead will become higher and higher.Exam Point Don't forget that the path overhead is incremented as BPDUs enter rather than leave the port.Selecting the Root PortIf the switch has multiple paths to the root switch to choose from, it needs to select one of them and thus elect the root port. The switch selects the root port by following the STP steps below. 1. When there are multiple paths to the root switch, select the path with the lowest cumulative path overhead.2. If multiple paths to the root switch have the same cumulative path overhead, the switch selects the neighboring switch with the lowest switch ID (the switch through which the path to the root switch is routed).to the root switch). 3. If multiple paths go through the same neighboring switches, the local port with the lowest priority value will be selected.4. If the ports have the same priority, the physical port with the lowest number will be selected. For example, on a 2960 switch, the lowest numbered physical port is FastEthemet 0/1 or Gigabit 0/1After this election process is complete, one and only one switch will be the root port.Exam Pointers