Port Roles

Root Port

The root port exists on non-root bridges and is the switch port with the best path to the root bridge.

Designated Port

The designated port exists on root and non-root bridges. For root bridges, all switch ports are designated ports. Only one designated port is allowed per segment. Designated ports are capable of populating the MAC table.

Non-designated Port

The non-designated port is a switch port that is blocked, so it is not forwarding data frames and not populating the MAC address table with source addresses.

Disabled Port

The disabled port is a switch port that is administratively shut down.

STP Port Roles

STP Port Roles

Configure port priority

Verify Port Roles and Priority

STP Port States and BPDU Timers

Port States:

Blocking

The port is a non-designated port and does not participate in frame forwarding. The port receives BPDU frames to determine the location and root ID of the root bridge switch and what port roles each switch port should assume in the final active STP topology.

Listening

STP has determined that the port can participate in frame forwarding according to the BPDU frames that the switch has received thus far. At this point, the switch port is not only receiving BPDU frames, it is also transmitting its own BPDU frames and informing adjacent switches that the switch port is preparing to participate in the active topology.

Learning

The port prepares to participate in frame forwarding and begins to populate the MAC address table.

Forwarding

The port is considered part of the active topology and forwards frames and also sends and receives BPDU frames.

Disabled

The Layer 2 port does not participate in spanning tree and does not forward frames. The disabled state is set when the switch port is administratively disabled.

STP Port States

BPDU Timers

BPDU Roles and Timers

Configure network diameter

PortFast

PortFast is a Cisco technology. When a switch port configured with PortFast is configured as an access port, that port transitions from blocking to forwarding state immediately, bypassing the typical STP listening and learning states.

Cisco Portfast technology

Configure portfast

Verify portfast

STP Convergence

STP Convergence

STP Convergence

Step 1. Electing A Root Bridge Electing a root bridge Step 2. Elect Root Ports Elect a root port step 1 Elect a root port step 2 Elect a root port step 3 Elect a root port step 4 Step 3. Electing Desgnated Ports and Non-Designated Ports Elect port step 1 Elect port step 2 Elect port step 3 Elect port step 4 Elect port step 5 Elect port step 6 Elect port step 7 STP Topology Change STP Topology Change Topology change notification(TCN) messages are flooded out the root port, until it reaches the root bridge. STP Broadcast notification The Root Bridge broadcasts Topology change messages PVST+, RSTP and Rapid-PVST+ Cisco and STP Variants STP Variants PVST+ PVST+ PVST+ Bridge ID PVST+ Bridge ID example Default PVST+ configuration Configure PVST+ Configure PVST+ Configure PVST+ Priority Verify PVST+ RSTP RSTP Characteristics of RSTP RSTP BPDU Edge Ports Edge Ports Link Types Link Types Point-to-point Link Type - Links attaches to switch ports that are operating in full-duplex mode Shared Link Type - This link is attached to a port that is operating in half-duplex mode RSTP Port States and Port Roles RSTP Port States RSTP Port States RSTP Port States RSTP Port Roles Configure Rapid-PVST+ Rapid-PVST+ Topology Rapid-PVST+ Example configuration Rapid-PVST+ verification Design STP for Trouble Avoidance Know where the root is Manual Pruning Layer 3 Switching Layer 3 Switching Troubleshoot STP Operation Troubleshoot a failure PortFast configuration error Network diameter issues Chapter Summary Chapter summary