Planet FGSD-1022P — understanding STP Port States in Network Switches [81/197]

User’s Manual of FGSD-1022 Series

Each port on a switch using STP exists is in one of the following five states:

 Blocking – the port is blocked from forwarding or receiving packets.

 Listening – the port is waiting to receive BPDU packets that may tell the port to go back to the blocking state.

 Learning – the port is adding addresses to its forwarding database, but not yet forwarding packets.

 Forwarding – the port is forwarding packets.

 Disabled – the port only responds to network management messages and must return to the blocking state

first.

A port transitions from one state to another as follows:

 From initialization (switch boot) to blocking.

 From blocking to listening or to disabled.

 From listening to learning or to disabled.

 From learning to forwarding or to disabled.

 From forwarding to disabled.

 From disabled to blocking.

Switch

Blocking

Listening

Learning

Forwarding

Disable

Figure 4-5-1: STP Port State Transitions

You can modify each port state by using management software. When you enable STP, every port on every switch in the

network goes through the blocking state and then transitions through the states of listening and learning at power up. If

properly configured, each port stabilizes to the forwarding or blocking state. No packets (except BPDUs) are forwarded from,

or received by, STP enabled ports until the forwarding state is enabled for that port.