Table Of Contents
Spanning Tree Protocol Interaction
REP Integrated with an EVC Port
REP Segments and REP Administrative VLANs
Configuring the REP Administrative VLAN
Guidelines for Configuring the REP Administrative VLAN
Setting the Preemption for VLAN Load-Balancing
Configuring SNMP Traps for REP
Monitoring the REP Configuration
Configuration Examples for REP
Configuring the REP Administrative VLAN: Example
Configuring a REP Interface: Example
Setting the Preemption for VLAN Load-Balancing: Example
Configuring SNMP Traps for REP: Example
Monitoring the REP Configuration: Example
Feature Information for Resilient Ethernet Protocol
Resilient Ethernet Protocol
First Published: January 31, 2008Last Updated: November 20, 2009
Resilient Ethernet Protocol (REP) is a Cisco proprietary protocol that provides an alternative to Spanning Tree Protocol (STP). REP provides a way to control network loops, handle link failures, and improve convergence time. REP controls a group of ports connected in a segment, ensures that the segment does not create any bridging loops, and responds to link failures within the segment. REP provides a basis for constructing more complex networks and supports VLAN load-balancing.
The router supports REP only when the router is running the metro IP access or metro access image.
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for Resilient Ethernet Protocol" section on page 20.
Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Contents
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Information About REP, page 2
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Information About REP
To configure the REP feature, you should understand the following concepts.
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REP Segments
One REP segment is a chain of ports connected to each other and configured with a segment ID. Each segment consists of standard (non-edge) segment ports and two user-configured edge ports. A router can have no more than two ports that belong to the same segment, and each segment port can have only one external neighbor. A segment can go through a shared medium, but on any link only two ports can belong to the same segment. REP is supported only on Layer 2 trunk interfaces.
Figure 1 shows an example of a segment consisting of six ports spread across four switches. Ports E1 and E2 are configured as edge ports. When all ports are operational (as in the segment on the left), a single port is blocked, shown by the diagonal line. When there is a failure in the network, the blocked port returns to the forwarding state to minimize network disruption.
Figure 1 REP Open Segments
The segment shown in Figure 1 is an open segment; there is no connectivity between the two edge ports. The REP segment cannot cause a bridging loop and it is safe to connect the segment edges to any network. All hosts connected to routers inside the segment have two possible connections to the rest of the network through the edge ports, but only one connection is accessible at any time. If a failure occurs on any segment or any port on a REP segment, REP unblocks all ports to ensure that connectivity is available through the other gateway.
The segment shown in Figure 2, with both edge ports located on the same router, is a ring segment. In this configuration, there is connectivity between the edge ports through the segment. With this configuration, you can create a redundant connection between any two routers in the segment.
Figure 2 REP Ring Segment
REP segments have the following characteristics:
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You can construct almost any type of network based on REP segments. REP also supports VLAN load-balancing, controlled by the primary edge port but occurring at any port in the segment.
REP has the following limitations:
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Link Integrity
REP does not use an end-to-end polling mechanism between edge ports to verify link integrity. It implements local link failure detection. When enabled on an interface, the REP Link Status Layer (LSL) detects its REP-aware neighbor and establishes connectivity within the segment. All VLANs are blocked on an interface until it detects the neighbor. After the neighbor is identified, REP determines which neighbor port should become the alternate port and which ports should forward traffic.
Each port in a segment has a unique port ID. The port ID format is similar to that used by the spanning tree algorithm: a port number (unique on the bridge), associated to a MAC address (unique in the network). When a segment port is coming up, its LSL starts sending packets that include the segment ID and the port ID. The port is declared as operational after it performs a three-way handshake with a neighbor in the same segment. A segment port does not become operational under the following conditions:
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Each port creates an adjacency with its immediate neighbor. Once the neighbor adjacencies are created, the ports negotiate to determine one blocked port for the segment, the alternate port. All other ports become unblocked. By default, REP packets are sent to a PortFast Bridge Protocol Data Unit (BPDU) class MAC address. The packets can also be sent to the Cisco multicast address, which at present is used only to send blocked port advertisement (BPA) messages when there is a failure in the segment. The packets are dropped by devices not running REP.
Fast Convergence
Because REP runs on a physical-link basis and not a per-VLAN basis, only one hello message is required for all VLANs, reducing the load on the protocol. We recommend that you create VLANs consistently on all switches in a given segment and configure the same allowed VLANs on the REP trunk ports. To avoid the delay introduced by relaying messages in software, REP also allows some packets to be flooded to a regular multicast address. These messages operate at the hardware flood layer (HFL) and are flooded to the whole network, not just the REP segment. Switches that do not belong to the segment treat the messages as data traffic. You can control flooding of these messages by configuring a dedicated administrative VLAN for the whole domain.
The estimated convergence recovery time is less than 200 ms for the local segment.
VLAN Load-Balancing
One edge port in the REP segment acts as the primary edge port; the other as the secondary edge port. It is the primary edge port that always participates in VLAN load-balancing in the segment. REP VLAN load-balancing is achieved by blocking some VLANs at a configured alternate port and all other VLANs at the primary edge port. When you configure VLAN load-balancing, you can specify the alternate port in one of three ways:
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When the REP segment is complete, all VLANs are blocked. When you configure VLAN load-balancing, it is triggered in one of two ways:
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When VLAN load-balancing is triggered, the primary edge port then sends out a message to alert all interfaces in the segment about the preemption. When the message is received by the secondary edge port, it is reflected into the network to notify the alternate port to block the set of VLANs specified in the message and to notify the primary edge port to block the remaining VLANs.
You can also configure a particular port in the segment to block all VLANs. VLAN load-balancing is initiated only by the primary edge port and is not possible if the segment is not terminated by an edge port on each end. The primary edge port determines the local VLAN load-balancing configuration.
To reconfigure VLAN load-balancing, you reconfigure the primary edge port. When you change the VLAN-load balancing configuration, the primary edge port again waits for the rep preempt segment command or for the configured preempt delay period after a port failure and recovery before executing the new VLAN 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 Spanning Tree Protocol (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 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 means multiple blocked ports and a potential loss of connectivity. When the segment has been configured in both directions up to the location of the edge ports, you then configure the edge ports.
REP Ports
Ports in REP segments take one of three roles or states: Failed, Open, or Alternate.
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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 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 Services (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 could be forwarded to another network provider edge (N-PE) router, breaking the split horizon model.
Figure 3 REP Integrated with VPLS
REP emulates a common link connection that so that the REP ring supports the VPLS full-mesh model, but maintains the split horizon properties so that the super-loop does not exist. The emulated common link uses the Clustering over the WAN (CWAN) linecard, 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; handles access pseudo-wire for H-VPLS topologies.
REP Integrated with an EVC Port
REP can be integrated with an EVC port by using the REP over Ethernet Virtual Circuit (EVC) feature. The REP over EVC feature, intended for use on the Cisco 7600 series router, allows you to configure and manage ports at service level. An EVC port can have multiple service instances. Each service instance corresponds to a unique Event Flow Processor (EFP). By default, REP is disabled on all ports. Using the REP over EVC feature, you can:
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The ports on a Cisco 7600 series router are classified into three different types: switchports, routed ports, and EVC ports. By default, a port is a routed port. REP is not supported on routed ports. You need to configure a port to a switchport or EVC port to configure REP on it. A port that is configured with one or more service instances is called an EVC port.
This feature allows you to configure an EVC port to participate in a REP segment. REP can selectively block or forward data traffic on particular VLANs. For EVC, the VLAN Id refers to the outer tag of the dot1q encapsulation that is configured on a service instance. REP is supported on a bridge-domain service. If the ethernet vlan color-block all command is configured, REP is supported on connect and xconnect services.
For more information about this feature, see the Cisco 7600-ES20 Ethernet Line Card Configuration Guide.
Default REP Configuration
REP is disabled on all interfaces. When enabled, the interface is a regular segment port unless it is configured as an edge port.
When REP is enabled, the sending of segment topology change notices (STCNs) is disabled, all VLANs are blocked, and the administrative VLAN is VLAN 1.
When VLAN load-balancing is enabled, the default is manual preemption with the delay timer disabled. If VLAN load balancing is not configured, the default after manual preemption is to block all VLANs at the primary edge port.
REP Segments and REP Administrative VLANs
A segment is a collection of ports connected one to the other in a chain and configured with a segment ID. To configure REP segments, you should configure the REP administrative VLAN (or use the default VLAN 1) and then add the ports to the segment using interface configuration mode. You should configure two edge ports in the segment, with one of them the primary edge port and the other by default the secondary edge port. A segment has only one primary edge port. If you configure two ports in a segment as the primary edge port, for example ports on different switches, the REP selects one of them to serve as the segment primary edge port. You can also optionally configure where to send segment topology change notices (STCNs) and VLAN load-balancing. For more information about configuring REP Administrative VLANS, see the "Configuring the REP Administrative VLAN" section on page 9.
REP Configuration Guidelines
Follow these guidelines when configuring REP:
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How to Configure REP
This section contains the following tasks:
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Configuring the REP Administrative VLAN
To configure the REP administrative VLAN, complete the following steps:
Guidelines for Configuring the REP Administrative VLAN
To avoid the delay introduced by relaying messages related to link-failure or VLAN-blocking notification during VLAN load-balancing, REP floods packets at the hardware flood layer (HFL) to a regular multicast address. These messages are flooded to the whole network, not just the REP segment. You can control flooding of these messages by configuring an administrative VLAN for the whole domain.
Follow these guidelines when configuring the REP administrative VLAN:
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Configuring REP Interfaces
To enable and configure REP on an interface, complete the following steps:
Prerequisite
For REP operation, you need to enable it on each segment interface and identify the segment ID. This step is required and must be done before other REP configurations. You must also configure a primary and secondary edge port on each segment. All other steps are optional.
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Setting the Preemption for VLAN Load-Balancing
To set the preemption for VLAN load-balancing, complete these steps on the router that has the segment with the primary edge port.
Restrictions
If you do not enter the rep preempt delay seconds interface configuration command on the primary edge port to configure a preemption time delay, the default is to manually trigger VLAN load-balancing on the segment. Use the show rep topology privileged EXEC command to see which port in the segment is the primary edge port.
Prerequisite
Be sure that all other segment configuration has been completed before setting preemption for VLAN load-balancing. When you enter the rep preempt segment segment-id command, a confirmation message appears before the command is executed because preemption for VLAN load-balancing can disrupt the network.
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Configuring SNMP Traps for REP
You can configure the router to send REP-specific traps to notify the SNMP server of link operational status changes and any port role changes. To configure REP traps, complete the following steps:
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Monitoring the REP Configuration
To monitor the REP configuration, complete the following steps:
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Configuration Examples for REP
This section provides the following configuration examples:
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Configuring the REP Administrative VLAN: Example
This example shows how to configure the administrative VLAN as VLAN 100.
Router# configure terminalRouter(config)# rep admin vlan 100Router(config-if)# endConfiguring a REP Interface: Example
This example shows how to configure an interface as the primary edge port for segment 1, to send Spanning Tree Topology Changes Notification (STCNs) to segments 2 through 5, and to configure the alternate port as the port with port ID 0009001818D68700 to block all VLANs after a preemption delay of 60 seconds after a segment port failure and recovery.
Router# configure terminalRouter(config)# interface gigabitethernet0/1Router(config-if)# rep segment 1 edge primaryRouter(config-if)# rep stcn segment 2-5Router(config-if)# rep block port 0009001818D68700 vlan allRouter(config-if)# rep preempt delay 60Router(config-if)# endThis example shows how to configure the VLAN blocking configuration shown in Figure 4. The alternate port is the neighbor with neighbor offset number 4. After manual preemption, VLANs 100-200 are blocked at this port and all other VLANs are blocked at the primary edge port E1 (Gigabit Ethernet port 0/1).
Router# configure terminalRouter(config)# interface gigabitethernet0/1Router(config-if)# rep segment 1 edge primaryRouter(config-if)# rep block port 4 vlan 100-200Router(config-if)# endFigure 4 Example of VLAN Blocking
Setting the Preemption for VLAN Load-Balancing: Example
The following is an example of setting the preemption for VLAN load-balancing on a REP segment.
Router> enable
Router# configure terminal
Router(config)# rep preempt segment 1
Router(config)# end
Configuring SNMP Traps for REP: Example
This example configures the router to send REP traps at a rate of 10 traps per second:
Router> enableRouter# configure terminalRouter(config)# snmp mib rep trap-rate 10Router(config)# endMonitoring the REP Configuration: Example
The following is sample output of the show interface rep detail command. Use the show interface rep detail command on one of the REP interfaces to monitor and verify the REP configuration.
Router# show interface gigabitethernet0/1 rep detailGigabitEthernet0/1 REP enabled Segment-id: 2 (Edge) PortID: 00010019E7144680 Preferred flag: No Operational Link Status: TWO_WAY Current Key: 0002001121A2D5800E4D Port Role: Open Blocked Vlan: <empty> Admin-vlan: 100 Preempt Delay Timer: disabled Load-balancing block port: none Load-balancing block vlan: none STCN Propagate to: none LSL PDU rx: 3322, tx: 1722 HFL PDU rx: 32, tx: 5 BPA TLV rx: 16849, tx: 508 BPA (STCN, LSL) TLV rx: 0, tx: 0 BPA (STCN, HFL) TLV rx: 0, tx: 0 EPA-ELECTION TLV rx: 118, tx: 118 EPA-COMMAND TLV rx: 0, tx: 0 EPA-INFO TLV rx: 4214, tx: 4190Additional References
The following sections provide references related to the Resilient Ethernet Protocol feature.
Related Documents
Cisco IOS commands
LAN Switching commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples.
Flex links
"Configuring Flex Links" chapter of the Catalyst 6500 Release 12.2SXH and Later Software Configuration Guide
Introduction to spanning tree protocols
Spanning Tree PortFast BPDU Guard Enhancement feature
Cisco IOS 7600 series routers
Standards
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
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MIBs
RFCs
No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.
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Technical Assistance
Feature Information for Resilient Ethernet Protocol
Table 1 lists the release history for this feature.
Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note
Table 1 Feature Information for Resilient Ethernet Protocol
Resilient Ethernet Protocol
12.2(44)SE
12.2(33)SRCREP is a Cisco proprietary protocol that provides an alternative to Spanning Tree Protocol (STP); it provides a way to control network loops, handle link failures, and improve convergence time. REP controls a group of ports connected in a segment, ensures that the segment does not create any bridging loops, and responds to link failures within the segment. REP provides a basis for constructing more complex networks and supports VLAN load balancing.
In 12.2(44)SE, this feature was introduced on the Cisco 3750 series router.
In 12.2(33)SRC, support was added for the Cisco 7600 series router and included integration with VPLS core networks.
The following commands were introduced or modified by this feature: rep admin vlan, rep block port, rep preempt delay, rep preempt segment, rep segment, rep stcn, show rep topology.
REP Integration with EVC and VPLS
12.2(33)SRE
REP can be integrated with an EVC and VPLS by using the REP over Ethernet Virtual Circuit (EVC) feature. The REP over EVC feature, intended for use on the Cisco 7600 series router, allows you to configure and manage ports at the service level.
For more information, see the following section:
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For more detailed information, see the Cisco 7600-ES20 Ethernet Line Card Configuration Guide.
No commands were introduced or modified by this feature.
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