Configuring Spanning Tree Protocol (STP) and IronSpan Features
December 2005 © Foundry Networks, Inc. 7 - 21
Edge Ports and Edge Port Roles
Foundry’s implementation of 802.1W allows ports that are configured as Edge ports to be present in an 802.1W
topology. (Figure 7.2). Edge ports are ports of a bridge that connect to workstations or computers. Edge ports do
not register any incoming BPDU activities.
Edge ports assume Designated port roles. Port flapping does not cause any topology change events on Edge
ports since 802.1W does not consider Edge ports in the spanning tree calculations.
Figure 7.2 Topology with Edge Ports
However, if any incoming RST BPDU is received from a previously configured Edge port, 802.1W automatically
makes the port as a non-edge port. This is extremely important to ensure a loop free Layer 2 operation since a
non-edge port is part of the active RSTP topology.
The 802.1W protocol can auto-detect an Edge port and a non-edge port. An administrator can also configure a
port to be an Edge port using the CLI. It is recommended that Edge ports are configured explicitly to take
advantage of the Edge port feature, instead of allowing the protocol to auto-detect them.
Point-to-Point Ports
To take advantage of the 802.1W features, ports on an 802.1W topology should be explicitly configured as point-
to-point links using the CLI. Shared media should not be configured as point-to-point links.
NOTE: Configuring shared media or non-point-to-point links as point-to-point links could lead to Layer 2 loops.
The topology in Figure 7.3 is an example of shared media that should not be configured as point-to-point links. In
Figure 7.3, a port on a bridge communicates or is connected to at least two ports.
Port2 Port2
Port3Port3
Port2
Port3
Port5
Edge Port
Port5
Edge Port
Bridge priority = 600
1Switch
Bridge priority = 2000
Switch 3
Bridge priority = 1000
2Switch
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