Spanning Tree Protocol Interaction; Rep Ports; Rep Integrated With Vpls - Cisco ASR 900 Series Configuration Manual
Lan switching
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Spanning Tree Protocol Interaction
load balancing configuration. If you change an edge port to a regular segment port, the existing VLAN load
balancing status does not change. Configuring a new edge port might cause a new topology configuration.
Spanning Tree Protocol Interaction
REP does not interact with STP or with Flex Links but can coexist with both of them. A port that belongs to
a segment is removed from spanning tree control, and STP BPDUs are not accepted or sent from segment
ports. Therefore, STP cannot run on a segment.
To migrate from an STP ring configuration to a REP segment configuration, begin by configuring a single
port in the ring as part of the segment and continue by configuring contiguous ports to minimize the number
of segments. Each segment always contains a blocked port, so multiple segments mean multiple blocked ports
and a potential loss of connectivity. You can configure the edge ports when the segment has been configured
in both directions up to the location of the edge ports.
REP Ports
Ports in REP segments take one of following three roles or states: Failed, Open, or Alternate.
• A port configured as a regular segment port starts as a failed port.
• After neighbor adjacencies are determined, the port transitions to the alternate port state, blocking all
• When a failure occurs in a link, all ports move to the failed state. When the alternate port receives the
A regular segment port converted to an edge port, or an edge port converted to a regular segment port, does
not always result in a topology change. If you convert an edge port into a regular segment port, VLAN load
balancing is not implemented unless it has been configured. For VLAN load balancing, you must configure
two edge ports in the segment.
A segment port that is reconfigured as a spanning tree port restarts according to the spanning tree configuration.
By default, this port is a designated blocking port. If the PortFast BPDU Guard Enhancement feature is
configured or if STP is disabled, the port goes into the forwarding state.
REP Integrated with VPLS
Normally, in a Virtual Private LAN Service (VPLS) network core, all nodes are connected in a full-mesh
topology and each node has connectivity to all other nodes. In the full-mesh topology, there is no need for a
node to retransmit data to another node. In Figure 3, the common ring provides a path where the packet can
be forwarded to another network provider edge (N-PE) router, breaking split horizon model.
REP emulates a common link connection the REP ring supports the VPLS full-mesh model, but maintains
the split horizon properties so the super-loop does not exist. The emulated common link uses the Clustering
over the WAN (CWAN) line card, which is also used for the VPLS uplink. This emulated common link
forwards data from the ring to either the VPLS uplink or to the other side of the ring; blocks data coming from
the VPLS core network; and handles access to pseudowire for Hierarchical-VPLS (H-VPLS) topologies.
LAN Switching Configuration Guide Cisco IOS XE Everest 16.5.1 (Cisco ASR 900 Series)
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VLANs on the interface. Blocked port negotiations occur, and when the segment settles, one blocked
port remains in the alternate role, and all other ports become open ports.
failure notification, the port changes to the open state forwarding all VLANs.
Configuring Resilient Ethernet Protocol
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