STP - Aging time reduction with a TCN

STP - Aging time return to default

STP - RSTP BPDU Flags and their usage

STP - RSTP while timer cannot be observed

STP - RSTP while timer

STP - Topology Change Acknowledgement (TCA)

STP Topology Change Timer

STP contents of a BPDU

STP topology change process


In an [STP](/spanning-tree-protocol-stp) topology, when a bridge receives a [BPDU](/stp-bpdu-types) with the Topology Change (TC) flag bit set, it reduces its [MAC](/switching-media-access-control-mac-addresses) [address table](/mac-address-table) aging time [from 300 seconds to 15 seconds](/stp-aging-time-reduction-with-a-tcn). This ensures a relatively quick flush of stale information.

According to the official documentation, it is only when a switch receives the TC BPDU from the root that the aging timer for the MAC address table is reduced, and not when it receives a TCN from a downstream switch. The only exception is the switch on which the topology change was detected. In such a case, the age timer of the MAC address table on the originator of the TCN is immediately reduced.

The TC flag plays a vital role in the [STP topology change process](/stp-topology-change-process).


STP Topology Change (TC) flag

STP - MST and PVST+ selecting root port

STP - MST maps groups of VLANs

STP - MST region attributes

STP - MST viewed as a single switch by PVST+

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 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 - Root Inconsistency State

STP - Root Link Query (RLQ) BPDU

STP - Shortest Path Bridging (SPB)

STP - Time to select root bridge

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 - UplinkFast

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 - spanning-tree root primary command

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 Best Practice

STP Portfast Options

STP Root Bridge selection

STP Root Guard

STP UDLD and Autonegotiation

STP UDLD

STP bridge priority values

STP changing link cost

STP configuring on EtherChannel

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

Security - 802.1x with WLC and AAA server

Security - AAA for RESTCONF

Security - Best Practices for Repurposing Network Devices

Security - Cisco AnyConnect Secure Mobility Client

Security - Cisco Secure Client

Security - Cisco VPN Client

Security - Cisco VPN client software

Security - Diffie-Hellman groups

Security - Extensible Authentication Protocol over LAN (EAPOL)

Security - GETVPN

Security - IEEE 802.1X

Security - IOS Usernames and Passwords

Security - IPsec nonce

Security - Kerberos

Security - MAC Authentication Bypass

Security - Network Access Control (NAC)

Security - Next Generation Firewall

Security - Secure Unique Device Identifier (SUDI)

Security - WPA 4-way handshake

Security - WebVPN

Security - accessing VTY from another VRF

Security - assigning privilege levels, syntax and behavior

Security - bogons

Security - broadcast-multicast storm

Security - configuring TACACS from another VRF

Security - privilege levels and command output

Security - privilege levels and enable keyword

Security - public key exchange

Security - root CAs and private keys

Security - spoofing

Security - storm control algorithm

Security IKE policy hash command

Security Trusted Platform Module (TPM)

STP Topology Change (TC) flag

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