Configuring Resilient Ethernet Protocol

Resilient Ethernet Protocol (REP) is a Cisco proprietary protocol that provides an alternative to Spanning Tree Protocol (STP) to control network loops, to respond to link failures, and to 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. Effective with Cisco IOS Release 15.4(1)S, the Cisco ASR 901 supports REP over port-channel.

Understanding Resilient Ethernet Protocol

This section contains the following topics:

Overview

An 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 switch can have only two ports belonging 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.

The following figure 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 network failure, as shown on the right of the diagram, the blocked port returns to the forwarding state to minimize network disruption.

Figure 1. REP Open Segments

The segment shown in the above figure is an open segment; there is no connectivity between the two edge ports. The REP segment cannot cause a bridging loop, and you can safely connect the segment edges to any network. All hosts connected to switches 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 host cannot access its usual gateway because of a failure, REP unblocks all ports to ensure that connectivity is available through the other gateway.

The segment shown in the following figure, with both edge ports located on the same switch, 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 switches in the segment.

Figure 2. REP Ring Segment

REP segments have these characteristics:

  • If all ports in the segment are operational, one port (referred to as the alternate port) is in the blocked state for each VLAN.

  • If VLAN load balancing is configured, two ports in the segment control the blocked state of VLANs.

  • If one or more ports in a segment is not operational, causing a link failure, all ports forward traffic on all VLANs to ensure connectivity.

  • In case of a link failure, the alternate ports are unblocked as quickly as possible. When the failed link comes back up, a logically blocked port per VLAN is selected with minimal disruption to the network.

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.

In access ring topologies, the neighboring switch might not support REP, as shown in the following figure. In this case, you can configure the non-REP facing ports (E1 and E2) as edge no-neighbor ports. These ports inherit all properties of edge ports, and you can configure them the same as any edge port, including configuring them to send STP or REP topology change notices to the aggregation switch. In this case the STP topology change notice (TCN) that is sent is a multiple spanning-tree (MST) STP message.

Figure 3. No-neighbor Topology

Restrictions

  • You must configure each segment port; an incorrect configuration can cause forwarding loops in the networks.
  • REP can manage only a single failed port within the segment; multiple port failures within the REP segment cause loss of network connectivity.
  • You should configure REP only in networks with redundancy. Configuring REP in a network without redundancy causes loss of connectivity.

  • BFD and REP together are not recommended on Cisco ASR 901 Router while sharing the same link.

  • Layer 3 over REP with VLAN load balancing is not recommended on Cisco ASR 901 Router.

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. 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 operational after it performs a three-way handshake with a neighbor in the same segment.

A segment port does not become operational if:

  • No neighbor has the same segment ID.
  • More than one neighbor has the same segment ID.
  • The neighbor does not acknowledge the local port as a peer.

Each port creates an adjacency with its immediate neighbor. After 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 BPDU class MAC address. 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 them 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 on fiber interfaces is less than 200 ms for the local segment with 200 VLANs configured. Convergence for VLAN load balancing is 300 ms or less.

VLAN Load Balancing (VLB)

One edge port in the REP segment acts as the primary edge port; the other as the secondary edge port. The primary edge port always participates in VLAN load balancing in the segment. REP VLAN 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:

  • Enter the port ID of the interface. To identify the port ID of a port in the segment, use the show interface rep detail interface configuration command for the port.

Note
Use rep platform vlb segment command on every Cisco ASR 901 router participating in the REP segment.
  • Enter the neighbor offset number of a port in the segment, which identifies the downstream neighbor port of an edge port. The neighbor offset number range is –256 to +256; a value of 0 is invalid. The primary edge port has an offset number of 1; positive numbers above 1 identify downstream neighbors of the primary edge port. Negative numbers identify the secondary edge port (offset number -1) and its downstream neighbors.

Note
You configure offset numbers on the primary edge port by identifying the downstream position from the primary (or secondary) edge port. Do not enter an offset value of 1 because that is the offset number of the primary edge port.

Neighbor Offset Numbers in a Segment shows neighbor offset numbers for a segment where E1 is the primary edge port and E2 is the secondary edge port. The red numbers inside the ring are numbers offset from the primary edge port; the black numbers outside the ring show the offset numbers from the secondary edge port. Note that you can identify all ports (except the primary edge port) by either a positive offset number (downstream position from the primary edge port) or a negative offset number (downstream position from the secondary edge port). If E2 became the primary edge port, its offset number would then be 1, and E1 would be -1.

  • By entering the preferred keyword to select the port that you previously configured as the preferred alternate port with the rep segment segment-id preferred interface configuration command.
Figure 4. Neighbor Offset Numbers in a Segment

When the REP segment is complete, all VLANs are blocked. When you configure VLAN load balancing, you must also configure triggers in one of two ways:

  • Manually trigger VLAN load balancing at any time by entering the rep preempt segment segment-id privileged EXEC command on the router that has the primary edge port.
  • Configure a preempt delay time by entering the rep preempt delay seconds interface configuration command. After a link failure and recovery, VLAN load balancing begins after the configured preemption time period elapses. Note that the delay timer restarts if another port fails before the time elapses.

Note
When VLAN load balancing is configured, it does not start working until triggered by either manual intervention or a link failure and recovery.

When VLAN load balancing is triggered, the primary edge port sends a message to alert all interfaces in the segment about the preemption. When the secondary port receives the message, 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. Only the primary edge port initiates VLAN load balancing, which 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.

Reconfigure the primary edge port to reconfigure load balancing. When you change the 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 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.


Note
The roles of primary and secondary edge ports is Alt when VLB is enabled. Use show rep topology command to check the roles of primary and secondary edge ports.

Spanning Tree Interaction

REP does not interact with MSTP, but the two can coexist. A port that belongs to a segment is removed from spanning tree control, and STP BPDUs are not accepted or sent from segment ports.

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 is configured in both directions to the edge ports, you then configure the edge ports.

REP Ports

Ports in REP segments are in the Failed, Open, or Alternate states. The various states REP ports go through are as follows:

  • A port configured as a regular segment port starts as a failed port.
  • After the neighbor adjacencies are determined, the port changes to alternate port state, blocking all 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.
  • When a failure occurs in a link, all ports move to the open state. When the alternate port receives the failure notification, it changes to the open state, forwarding all VLANs.

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 reconfigured as a spanning tree port restarts according to the spanning tree configuration. By default, this is a designated blocking port. If PortFast is configured or if STP is disabled, the port goes into the forwarding state.

For instructions on how to configure REP, see Configuring Resilient Ethernet Protocol.

Configuring Resilient Ethernet Protocol

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 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 a service instance with encapsulation corresponding to the REP admin VLAN and associate it to arbitratory bridge domain.


Note
The explicit configuration of EFP gives you the flexibility to choose the bridge domain of your choice.

You should configure two edge ports in the segment, one as 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 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 messages.

This section contains the following topics:

Default REP Configuration

By default, 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 Configuration Guidelines

Follow these guidelines when configuring REP:

  • We recommend that you begin by configuring one port and then configure the contiguous ports to minimize the number of segments and the number of blocked ports.
  • If more than two ports in a segment fail when no external neighbors are configured, one port goes into a forwarding state for the data path to help maintain connectivity during configuration. In the show rep interface command output, the Port Role for this port shows as Fail Logical Open ; the Port Role for the other failed port shows as Fail No Ext Neighbor . When the external neighbors for the failed ports are configured, the ports go through the alternate port state transitions and eventually go to an open state or remain as the alternate port, based on the alternate port election mechanism.
  • REP ports must be Layer 2 ports.
  • Be careful when configuring REP through a Telnet connection. Since REP blocks all VLANs until another REP interface sends a message to unblock the VLAN, you might lose connectivity to the router if you enable REP in a Telnet session that accesses the router through the REP interface.
  • If you connect an STP network to the REP segment, be sure that the connection is at the segment edge. An STP connection that is not at the edge could cause a bridging loop because STP does not run on REP segments. All STP BPDUs are dropped at REP interfaces.
  • You must configure all ports in the segment with the same set of allowed VLANs, or a misconfiguration occurs.
  • REP ports follow these rules:
    • There is no limit to the number of REP ports on a switch; however, only two ports on a switch can belong to the same REP segment.
    • If only one port on a switch is configured in a segment, the port should be an edge port.
    • If two ports on a switch belong to the same segment, they must be both edge ports, both regular segment ports, or one regular port and one edge no-neighbor port. An edge port and regular segment port on a switch cannot belong to the same segment.
    • If two ports on a switch belong to the same segment and one is configured as an edge port and one as a regular segment port (a misconfiguration), the edge port is treated as a regular segment port.
  • REP interfaces come up and remain in a blocked state until notified that it is safe to unblock. You need to be aware of this to avoid sudden connection losses.
  • You should configure service instance with encapsulation corresponding to the REP admin VLAN and associate it to arbitratory Bridge Domain. This explicit configuration of EFP gives you the flexibility to choose the bridge domain of your choice.
  • REP sends all LSL PDUs in untagged frames on the native VLAN. The BPA message sent to the Cisco multicast address is sent on the administration VLAN, which is VLAN 1 by default.

  • You can configure the duration to keep REP interface alive without receiving a hello message from a neighbor using the rep lsl-age-timer value interface configuration command. Valid values range from 120 ms to 10000 ms. When this command is configured, the hello timer is set to the age-timer value divided by three. In normal REP operation, three LSL hellos are sent before the age-timer on the peer switch expires.

  • You should configure the rep platform fast-lsl enable command to support the REP sessions with LSL timers that are less than one second long. This command helps to detect the link failures in copper or microwave ports faster as the link failure detection takes longer time for these ports. Configuring the rep platform fast-lsl enable command helps to get optimal performance for copper or microwave ports. When this command is configured, you can expect only subsecond convergence for REP. The subsecond convergence period is also applicable for normal REP sessions, if fast LSL is configured.

  • REP ports cannot be configured as one of these port types:
    • SPAN destination port
    • Private VLAN
    • Tunnel port
    • Access port
  • There is a maximum of 128 REP segments per router.

Configuring the REP Administrative VLAN

To avoid the delay introduced by relaying messages in software for link-failure or VLAN-blocking notification during 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:

  • If you do not configure an administrative VLAN, the default is VLAN 1.
  • There can be only one administrative VLAN on a router and on a segment. However, this is not enforced by the software.
  • For VLB to work, rep platform vlb has to be configured on every Cisco ASR 901router participating in the segment.

Complete the following steps to configure the REP administrative VLAN:

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Router> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.
Step 2

configure terminal

Example:


Router# configure terminal

Enters global configuration mode.

Step 3

rep admin vlan vlan-id

Example:


Router(config)# rep admin vlan 1

Configures a REP administrative VLAN.

  • vlan-id --Specify the administrative VLAN. The range is 1–4094. The default is VLAN 1.
Step 4

end

Example:


Router(config)# end

Returns to privileged EXEC mode.

Step 5

show interface [interface-id ] rep [detail ]

Example:


Router# show interface gigabitethernet0/1 rep detail

Displays the REP configuration and status for a specified interface.

  • Enter the physical Layer 2 interface or port channel (logical interface) and the optional detail keyword, if desired.
Step 6

copy running-config startup config

Example:


Router# copy running-config startup config

(Optional) Saves your entries in the router startup configuration file.

Configuring REP Interfaces

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 configuration. You must also configure a primary and secondary edge port on each segment. All other steps are optional.

Complete these steps to enable and configure REP on an interface:

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Router> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.
Step 2

configure terminal

Example:


Router# configure terminal

Enters global configuration mode.

Step 3

interface interface-name interface-id

Example:


Router(config)# interface port-channel 1

Specifies the interface, and enters interface configuration mode.

  • Enter the physical Layer 2 interface or port channel ID. The port-channel range is 1 to 8.
Step 4

service instance instance-id ethernet encap dot1q admin-vlan rewrite ingress tag pop 1 symmetric bridge-domain bd-id

Example:


Router(config-if)# service instance 1 ethernet 
encap dot1q 1 rewrite ingress tag pop 1 symmetric bridge-domain 1

Configures ethernet virtual circuit for the administrative VLAN.

Step 5

rep segment segment-id [edge [no-neighbor ] [primary ]] [preferred

Example:


Router(config-if)# rep segment 1 edge preferred

Enables REP on the interface, and identifies a segment number. The segment ID range is from 1 to 1024.

Note 
You must configure two edge ports, including one primary edge port for each segment.

These are the optional keywords:

  • Enter the edge keyword to configure the port as an edge port. Entering edge without the primary keyword configures the port as the secondary edge port. Each segment has only two edge ports.
  • (Optional) Enter the no-neighbor keyword to configure a port with no external REP neighbors as an edge port. The port inherits all properties of edge ports, and you can configure them the same as any edge port.
  • On an edge port, enter the primary keyword to configure the port as the primary edge port, the port on which you can configure VLAN load balancing.
Note 
Although each segment can have only one primary edge port, if you configure edge ports on two different switches and enter the primary keyword on both switches, the configuration is allowed. However, REP selects only one of these ports as the segment primary edge port. You can identify the primary edge port for a segment by entering the show rep topology privileged EXEC command.
  • Enter the preferred keyword to indicate that the port is the preferred alternate port or the preferred port for VLAN load balancing.
Note 
Configuring a port as preferred does not guarantee that it becomes the alternate port; it merely gives it a slight edge among equal contenders. The alternate port is usually a previously failed port.
Step 6

rep lsl-retries number-of-retries

Example:


Router(config-if)# rep lsl-retries 4

Use the rep lsl-retries command to configure the REP link status layer (LSL) number of retries before the REP link is disabled.

Step 7

rep stcn {interface interface-id | segment id-list | stp }

Example:


Router(config-if)# rep stcn segment 2-5

(Optional) Configures the edge port to send segment topology change notices (STCNs).

  • Enter interface interface-id to designate a physical Layer 2 interface or port channel to receive STCNs.
  • Enter segment id-list to identify one or more segments to receive STCNs. The range is from 1–1024.
  • Enter stp to send STCNs to STP networks.
Step 8

rep platform vlb segment segment-id vlan {vlan-list | all }

Example:


Router(config)# rep platform vlb 
segment 1 vlan 100-200

(Optional) Configures the VLAN list which forms the VLB group. This command should be issued on all Cisco ASR 901 routers participating in VLB for a particular segment and should have a matching VLAN list. This VLAN list should also match with the rep block command issued on primary edge port.

  • Enter vlan vlan-list to block a single VLAN or a range of VLANs,
  • Enter vlan all to block all VLANs. This is the default configuration.
Step 9

rep block port {id port-id | neighbor-offset | preferred } vlan {vlan-list | all }

Example:


Router(config-if)# rep block 
port 0009001818D68700 vlan all

(Optional) Configures VLAN load balancing on the primary edge port, identifies the REP alternate port in one of three ways, and configures the VLANs to be blocked on the alternate port.

  • Enter the id port-id to identify the alternate port by port ID. The port ID is automatically generated for each port in the segment. You can view interface port IDs by entering the show interface interface-id rep [detail ] privileged EXEC command.
  • Enter a neighbor-offset number to identify the alternate port as a downstream neighbor from an edge port. The range is from –256 to 256, with negative numbers indicating the downstream neighbor from the secondary edge port. A value of 0 is invalid. Enter -1 to identify the secondary edge port as the alternate port.
Note 
Because you enter this command at the primary edge port (offset number 1), you would never enter an offset value of 1 to identify an alternate port.
  • Enter the preferred keyword to select the regular segment port previously identified as the preferred alternate port for VLAN load balancing.
  • Enter vlan vlan-list to block one VLAN or a range of VLANs.
  • Enter vlan all to block all VLANs.
Note 
Enter this command only on the REP primary edge port.
Step 10

rep preempt delay seconds

Example:


Router(config-if)# rep preempt delay 60

(Optional) Configures a preempt time delay. Use this command if you want VLAN load balancing to automatically trigger after a link failure and recovery. The time delay range is 15 to 300 seconds. The default is manual preemption with no time delay.

Note 
Use this command only on the REP primary edge port.
Step 11

rep lsl-age-timer value

Example:


Router(config-if) rep lsl-age-timer 5000

(Optional) Configure a time (in milliseconds) for which the REP interface remains up without receiving a hello from a neighbor. The range is from 120 to 10000 ms in 40-ms increments; the default is 5000 ms (5 seconds).

Step 12

rep platform fast-lsl enable

Example:


Router(config-if)# rep platform fast-lsl enable

Enables fast Link Status Layer (LSL) configuration to support the REP sessions with LSL timers that are less than one second long. When this command is configured, you can expect only subsecond convergence for REP. The subsecond convergence period is also applicable for normal REP sessions, if fast LSL is configured.

Step 13

end

Example:


Router(config-if)# end

Returns to privileged EXEC mode.

Step 14

show interface [interface-id ] rep [detail ]

Example:


Router# show interface gigabitethernet0/1 rep detail

Verifies the REP interface configuration.

  • Enter the physical Layer 2 interface or port channel (logical interface) and the optional detail keyword, if desired.
Step 15

show rep topology [segment segment-id ] [archive] [detail]

Example:


Router# show rep topology segment 1

Indicates which port in the segment is the primary edge port.

Step 16

copy running-config startup config

Example:


Router# copy running-config startup config

(Optional) Saves your entries in the router startup configuration file.

Configuring REP as Dual Edge No-Neighbor Port

For REP operation, you need to enable it on each segment interface and identify the segment ID.

Effective with Cisco IOS release 15.4.(1)S, you can configure the non-REP switch facing ports on a single device as dual edge no-neighbor ports. These ports inherit all properties of edge ports, and overcome the limitation of not converging quickly during a failure.

Figure 5. Dual Edge No-neighbor Topology

In access ring topologies, the neighboring switch might not support Dual Edge No-neighbor Topology Figure 12-5 . In this case, you can configure the non-REP facing ports (E1 and E2) as edge no-neighbor ports. These ports inherit all properties of edge ports, and you can configure them the same as any edge port, including configuring them to send STP or REP topology change notices to the aggregation switch. In this case the STP topology change notice (TCN) that is sent is a multiple spanning-tree (MST) STP message.

Complete these steps to enable and configure REP as dual edge no-neighbor port:

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Router> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.
Step 2

configure terminal

Example:


Router# configure terminal

Enters global configuration mode.

Step 3

interface interface-id

Example:


Router(config)# interface port-channel 1

Specifies the interface, and enters interface configuration mode.

  • Enter the physical Layer 2 interface or port channel ID. The port-channel range is 1 to 8.
Step 4

rep segment segment-id edge no-neighbor [primary | preferred

Example:


Router(config-if)# rep segment 1 edge no-neighbor preferred

Enables REP on the interface, and identifies a segment number. The segment ID range is from 1 to 1024.

Note 
You must configure two edge ports, including one primary edge port for each segment.

These are the optional keywords:

  • Enter the edge keyword to configure the port as an edge port. Entering edge without the primary keyword configures the port as the secondary edge port. Each segment has only two edge ports.
  • Enter the no-neighbor keyword to configure a port with no external REP neighbors as an edge port. The port inherits all properties of edge ports, and you can configure them the same as any edge port.
  • On an edge port, enter the primary keyword to configure the port as the primary edge port, the port on which you can configure VLAN load balancing.
Note 
Although each segment can have only one primary edge port, if you configure edge ports on two different switches and enter the primary keyword on both switches, the configuration is allowed. However, REP selects only one of these ports as the segment primary edge port. You can identify the primary edge port for a segment by entering the show rep topology privileged EXEC command.
  • Enter the preferred keyword to indicate that the port is the preferred alternate port or the preferred port for VLAN load balancing.
Note 
Configuring a port as preferred does not guarantee that it becomes the alternate port; it merely gives it a slight edge among equal contenders. The alternate port is usually a previously failed port.

What to do next


Note
For configuring REP LSL timer and VLB, see Configuring REP Interfaces.

Cisco ASR 901 Dual Rep Edge No-Neighbor Topology Example

The following configuration example shows a Cisco ASR 901 router running with Dual REP Edge No-Neighbor and two Cisco 7600 series routers running as non-REP devices.


Note
This section provides partial configurations intended to demonstrate a specific feature.
ASR_1

interface GigabitEthernet0/0
service instance 1 ethernet
  encapsulation dot1q 1
  rewrite ingress tag pop 1 symmetric
  bridge-domain 1
 !
 service instance 2 ethernet
  encapsulation dot1q 2
  rewrite ingress tag pop 1 symmetric
  bridge-domain 2
 !
rep segment 1 edge no-neighbor primary
!
interface GigabitEthernet0/1
 service instance 1 ethernet
  encapsulation dot1q 1
  rewrite ingress tag pop 1 symmetric
  bridge-domain 1
 !
 service instance 2 ethernet
  encapsulation dot1q 2
  rewrite ingress tag pop 1 symmetric
  bridge-domain 2
 !
rep segment 1 edge no-neighbor preferred
!
interface Vlan1
ip address 172.18.40.70 255.255.255.128
no ptp enable
!
interface Vlan2
ip address 1.1.1.1 255.255.255.0
no ptp enable
!
interface Vlan3
ip address 2.2.2.2 255.255.255.0
no ptp enable
!
interface Vlan3
ip address 4.4.4.2 255.255.255.0
no ptp enable
!
ip route 3.3.3.0 255.255.255.0 1.1.1.2
ip route 5.5.5.0 255.255.255.0 1.1.1.2
7600_1

interface Port-channel69
switchport
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,2
switchport mode trunk
!
interface GigabitEthernet3/25
switchport
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,2
switchport mode trunk
channel-group 69 mode on
!
interface GigabitEthernet3/26
switchport
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,2
switchport mode trunk
channel-group 69 mode on
!
interface GigabitEthernet3/35
ip address 3.3.3.2 255.255.255.0
!
interface GigabitEthernet3/36
ip address 5.5.5.2 255.255.255.0
!
interface GigabitEthernet5/2
switchport
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,2
switchport mode trunk
!
interface Vlan1
no ip address
!
interface Vlan2
ip address 1.1.1.2 255.255.255.0
!
ip route 2.2.2.0 255.255.255.0 1.1.1.1
ip route 4.4.4.0 255.255.255.0 1.1.1.1
7600_2

interface Port-channel69
switchport
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,2
switchport mode trunk
!
interface GigabitEthernet7/25
switchport
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,2
switchport mode trunk
channel-group 69 mode on
!
interface GigabitEthernet7/26
switchport
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,2
switchport mode trunk
channel-group 69 mode on
!
interface GigabitEthernet5/2
switchport
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,2
switchport mode trunk
!
interface Vlan1
no ip address
!
interface Vlan2
ip address 1.1.1.3 255.255.255.0

Setting up Manual Preemption for VLAN Load Balancing

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. Be sure to complete all other segment configuration before manually preempting VLAN load balancing. When you enter the rep preempt segment segment-id command, a confirmation message appears before the command is executed because preemption can cause network disruption.


Note
Ethernet over Multiprotocol Label Switching (EoMPLS) is supported on the Cisco ASR 901 router for Cisco IOS Release 15.2(2)SNG and later releases.

Complete these steps on the switch that has the segment primary edge port to manually trigger VLAN load balancing on a segment:

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Router> enable

Enables the privileged EXEC mode.

  • Enter your password if prompted.
Step 2

configure terminal

Example:


Router# configure terminal

Enters the global configuration mode.

Step 3

rep preempt segment segment-id

Example:


Router# rep preempt segment 1

Manually triggers VLAN load balancing on the segment.

  • Enter the segment ID.
Note 
You will be asked to confirm the action before the command is executed.
Step 4

end

Example:


Router(config)# end

Returns to the privileged EXEC mode.

Step 5

show rep topology

Example:


Router# show rep topology

Views the REP topology information.

Configuring SNMP Traps for REP

You can configure the switch to send REP-specific traps to notify the SNMP server of link operational status changes and port role changes. Complete these steps to configure REP traps:

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Router> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.
Step 2

configure terminal

Example:


Router# configure terminal

Enters global configuration mode.

Step 3

snmp mib rep trap-rate value

Example:


Router(config)# snmp mib rep trap-rate 500

Enables the router to send REP traps, and sets the number of traps sent per second.

  • Enter the number of traps sent per second. The range is from 0 to 1000. The default is 0 (no limit imposed; a trap is sent at every occurrence).
Note 
To remove the traps, enter the no snmp mib rep trap-rate command.
Step 4

end

Example:


Router(config)# end

Returns to privileged EXEC mode.

Step 5

show running-config

Example:


Router# show running-config

(Optional) Displays the running configuration, which you can use to verify the REP trap configuration.

Step 6

copy running-config startup config

Example:


Router# copy running-config startup config

(Optional) Saves your entries in the router startup configuration file.

Monitoring REP

Complete the following steps to monitor the REP configuration:

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Router> enable

Enables the privileged EXEC mode.

  • Enter your password if prompted.
Step 2

show interface [type number ] rep [ detail ]

Example:


Router# show interface gigabitethernet0/1 rep detail

(Optional) Displays the REP configuration and status for a specified interface.

  • Enter the physical Layer 2 interface or port channel (logical interface) and the optional detail keyword, if desired.
Step 3

show rep topology [segment segment-id ] [archive ] [detail ]

Example:


Router# show rep topology

(Optional) Displays REP topology information for a segment or for all segments, including the primary and secondary edge ports in the segment.

  • Enter the optional keywords and arguments, as desired.

Configuration Examples for REP

This section contains the following examples:

Configuring the REP Administrative VLAN: Example

This example shows how to configure the administrative VLAN as VLAN 100. 


Router# configure terminal
Router(config)# rep admin vlan 100
Router(config-if)# end

Configuring 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 terminal
Router(config)# interface gigabitethernet0/1
Router(config-if)# rep
 segment 1 edge primary
 
Router(config-if)# rep stcn segment 2-5 
Router(config-if)# rep block port 0009001818D68700 vlan all
Router(config-if)# rep preempt delay 60 
Router (config-if)# rep lsl-age-timer 6000 
Router(config-if)# end

This example shows how to configure the same configuration when the interface has no external REP neighbor: 


Router# configure terminal
Router(conf)# interface gigabitethernet0/1
Router(config-if)# rep segment 1 edge no-neighbor primary 
Router(config-if)# rep stcn segment 2-5 
Router(config-if)# rep block port 0009001818D68700 vlan all
Router(config-if)# rep preempt delay 60 
Router(config-if)# rep lsl-age-timer 6000

Example of VLAN Blocking shows how to configure the VLAN blocking configuration. The alternate port is the neighbor with neighbor offset number 4. After manual preemption, VLANs 100 to 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 terminal
Router(config)# interface gigabitethernet0/1
Router(config-if)# rep
 segment 1 edge primary
 
Router(config-if)# rep block port 4 vlan 100-200
Router(config-if)# end
Router(config)# rep platform vlb segment 1 vlan 100-200
Figure 6. Example of VLAN Blocking

Setting up 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# rep preempt segment 1

Router# end

Configuring SNMP Traps for REP: Example

This example shows how to configure the router to send REP traps at a rate of 10 traps per second: 


Router> enable
Router# configure terminal
Router(config)# snmp mib rep trap-rate 10
Router(config)# end

Monitoring 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 detail

GigabitEthernet0/1 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: 4190

Cisco Cisco ASR 901 Topology Example

The following configuration example shows two Cisco Cisco ASR 901 routers and two Cisco 7600 series routers using a REP ring.


Note
This section provides partial configurations intended to demonstrate a specific feature.

ASR_1


interface GigabitEthernet0/0
service instance 1 ethernet
  encapsulation dot1q 1
  rewrite ingress tag pop 1 symmetric
  bridge-domain 1
 !
 service instance 2 ethernet
  encapsulation dot1q 2
  rewrite ingress tag pop 1 symmetric
  bridge-domain 2
 !
rep segment 1
!
interface GigabitEthernet0/1
 service instance 1 ethernet
  encapsulation dot1q 1
  rewrite ingress tag pop 1 symmetric
  bridge-domain 1
 !
 service instance 2 ethernet
  encapsulation dot1q 2
  rewrite ingress tag pop 1 symmetric
  bridge-domain 2
 !
rep segment 1
!
interface GigabitEthernet0/3
 service instance 3 ethernet
  encapsulation dot1q 3
  rewrite ingress tag pop 1 symmetric
  bridge-domain 3
!
interface GigabitEthernet0/4
service instance 4 ethernet
  encapsulation dot1q 4
  rewrite ingress tag pop 1 symmetric
  bridge-domain 4
!
interface Vlan1
ip address 172.18.40.70 255.255.255.128
no ptp enable
!
interface Vlan2
ip address 1.1.1.1 255.255.255.0
no ptp enable
!
interface Vlan3
ip address 2.2.2.2 255.255.255.0
no ptp enable
!
interface Vlan3
ip address 4.4.4.2 255.255.255.0
no ptp enable
!
ip route 3.3.3.0 255.255.255.0 1.1.1.4
ip route 5.5.5.0 255.255.255.0 1.1.1.4

ASR_2


interface GigabitEthernet0/0
service instance 1 ethernet
  encapsulation dot1q 1
  rewrite ingress tag pop 1 symmetric
  bridge-domain 1
 !
 service instance 2 ethernet
  encapsulation dot1q 2
  rewrite ingress tag pop 1 symmetric
  bridge-domain 2
 !
rep segment 1
interface GigabitEthernet0/1
service instance 1 ethernet
  encapsulation dot1q 1
  rewrite ingress tag pop 1 symmetric
  bridge-domain 1
 !
 service instance 2 ethernet
  encapsulation dot1q 2
  rewrite ingress tag pop 1 symmetric
  bridge-domain 2
 !
rep segment 1
!
interface Vlan1
ip address 172.18.44.239 255.255.255.0
no ptp enable
!
interface Vlan2
ip address 1.1.1.2 255.255.255.0
no ptp enable

7600_1


interface Port-channel69
switchport
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,2
switchport mode trunk
!
interface GigabitEthernet3/25
switchport
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,2
switchport mode trunk
channel-group 69 mode on
!
interface GigabitEthernet3/26
switchport
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,2
switchport mode trunk
channel-group 69 mode on
!
interface GigabitEthernet3/35
ip address 3.3.3.2 255.255.255.0
!
interface GigabitEthernet3/36
ip address 5.5.5.2 255.255.255.0
!
interface GigabitEthernet5/2
switchport
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,2
switchport mode trunk
rep segment 1 edge
interface Vlan1
no ip address
!
interface Vlan2
ip address 1.1.1.4 255.255.255.0
!
ip route 2.2.2.0 255.255.255.0 1.1.1.1
ip route 4.4.4.0 255.255.255.0 1.1.1.1

7600_2


interface Port-channel69
switchport
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,2
switchport mode trunk
!
interface GigabitEthernet5/2
switchport
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,2
switchport mode trunk
rep segment 1 edge
!
interface GigabitEthernet7/25
switchport
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,2
switchport mode trunk
channel-group 69 mode on
!
interface GigabitEthernet7/26
switchport
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,2
switchport mode trunk
channel-group 69 mode on
!
interface Vlan1
no ip address
!
interface Vlan2
ip address 1.1.1.3 255.255.255.0