Edge Port Behavior

In ExtremeXOS 11.5 or earlier, Extreme Networks had two edge port implementations: edge port and edge port with safeguard.

The 802.1D-2004 standard has a bridge detection state machine, which introduced a third implementation of edge port behavior. The following list describes the behaviors of the different edge port implementations:

Edge port (ExtremeXOS 11.5 and earlier):
- The port does not send bridge protocol data units (BPDUs).
- The port does not run a state machine.
- If BPDUs are received, the port discards the BPDU and enters the blocking state.
- If subsequent BPDUs are not received, the port remains in the forwarding state.
Edge port with safeguard configured (ExtremeXOS 11.5 and 11.4 only):
- The port sends BPDUs.
- When configured for MSTP (Multiple Spanning Tree Protocol), the port runs a partial state machine.
- If BPDUs are received, the port enters the blocking state.
- If subsequent BPDUs are not received, the port attempts to enter the forwarding state.
Edge port running 802.1D-2004 with safeguard enabled:
- The port sends BPDUs.
- The port runs a state machine.
- If BPDUs are received, the port behaves as a normal RSTP port by entering the forwarding state and participating in RSTP.
- If subsequent BPDUs are not received, the port attempts to become the edge port again.

Edge port with safeguard prevents accidental or deliberate misconfigurations (loops) by having edge ports enter the blocking state upon receiving a BPDU. The 802.1D-2004 standard implements a bridge detection mechanism that causes an edge port to transition to a non-edge port upon receiving a BPDU; however, if the former edge port does not receive any subsequent BPDUs during a pre-determined interval, the port attempts to become an edge port.

If an 802.1D-2004 compliant safeguard port (edge port) connects to an 802.1D-1998 compliant edge port with safeguard configured, the old safeguard port enters the blocking state. Although the new safeguard port becomes a designated port, the link is not complete (and thus no loop is formed) because one side of the link is blocked.

Published March 2020prev | next

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