HSRP - Deployment in Distribution Layer

STP - UplinkFast

STP - spanning-tree root primary command


In Spanning Tree Protocol (STP), the bridge priority determines the root bridge in the network:

[STP how to find the root bridge](/stp-how-to-find-the-root-bridge)

Valid values for bridge priorities are between 0 and 61440, but the value must be in increments of 4096. This is because the VLAN ID is a 12-bit value that can represent up to 4096 VLAN IDs. The Bridge Priority is effectively a 4-bit value and is stored in a 16-bit field along with the VLAN ID:

![stp-bridge-priority-vlan-id.excalidraw](/attachments/excalidraw/stp-bridge-priority-vlan-id.excalidraw.svg)

In the Per-VLAN Spanning Tree Plus (PVST+) variant of STP, which is common on Cisco devices, the 2-byte (16-bit) Priority field in the BPDU is divided into two parts. The most significant 4 bits are for the Priority, and the least significant 12 bits are for the VLAN ID. 

Thus only Bridge priorities incremented in steps of 2^12 (4096) are valid. For instance, a bridge with a set priority of 12288 that is using VLAN 7 will actually have a priority value in the BPDU field of 12288+7 = 12295. That priority value is unique to VLAN 7 since there can be a root bridge for each individual VLAN, and the priorities must be unique.

STP bridge priority values

STP - Max Age vs Message Age

STP - Multiple Spanning Tree (MST)

STP - Multiple types of STP on the same switch

STP - PVST+ and Rapid PVST+ interaction

STP - Per VLAN Spanning Tree plus (PVST+)

STP - RSTP BPDU Flags and their usage

STP - RSTP EdgePort

STP - RSTP Proposal Timer Operation

STP - RSTP convergence process

STP - RSTP port roles

STP - RSTP prerequisites for immediate move to forward state

STP - RSTP proposal-agreement process

STP - RSTP while timer cannot be observed

STP - RSTP while timer

STP - Root Inconsistency State

STP - Root Link Query (RLQ) BPDU

STP - Shortest Path Bridging (SPB)

STP - Time to select root bridge

STP - Topology Change Acknowledgement (TCA)

STP - UDLD and Fiber Links

STP - Understanding MST regional root identifier and proposal-agreement process

STP - UplinkFast and reconvergence

STP - UplinkFast and root port delay timer

STP - bridge priority

STP - connecting one port to another port on the same switch

STP - determining the blocked port using port ID

STP - port identification

STP - port roles

STP - port states

STP - what bridge ID does the MST region use

STP - what is a topology change

STP BPDU Filter

STP BPDU Guard

STP BPDU Types

STP BPDU destination MAC address

STP Cost Calculation Methods

STP Loop Guard

STP Max Age

STP Message Age

STP PortFast

STP Portfast Options

STP Root Bridge selection

STP Root Guard

STP Topology Change (TC) flag

STP Topology Change Timer

STP UDLD and Autonegotiation

STP UDLD

STP changing link cost

STP configuring on EtherChannel

STP configuring portfast

STP contents of a BPDU

STP cost long mode

STP cost short mode

STP determining blocked port using cost

STP direct vs indirect link failure

STP fine tuning the spanning tree protocol

STP how a switch identifies a BPDU

STP how to find the root bridge

STP interface type

STP prio nbr value

STP topology change process

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STP bridge priority values

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