LAN Switching Configuration Guide, Cisco IOS XE Gibraltar 16.10.x
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The Resilient Ethernet Protocol (REP) is a Cisco proprietary protocol that provides an alternative to the Spanning Tree Protocol
(STP). REP provides a way to control network loops, handle link failures, and improve convergence time. It 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 complex networks and supports VLAN load balancing.
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Restrictions for Resilient
Ethernet Protocol
With respect to control frames, REP ALT port will block only tagged (part of Trunk EFP) control frames and not untagged (part
of Untagged EFP) control frames.
You must
configure each segment port; an incorrect configuration can cause forwarding
loops in networks.
REP can manage
only a single failed port within the segment; multiple port failures within the
REP segment causes high loss of network connectivity.
You should
configure REP only in networks with redundancy. Configuring REP in a network
without redundancy causes loss of network connectivity.
Use LSL timers of 520mseconds to avoid REP flaps.
The rate at which the layer 3 packets are punted to Host Q must be
lesser than 1000 packets/second to avoid REP flap. The credit limit for Host Q
is 1000 packets/second.
There is no drop in REP LSL packet in STP Queue.
The recommended
minimum REP LSL timer value is 200 ms.
The REP ports are removed from the topology list during the following situations:
New port is added after the removal of the old port.
Both REP ports are removed.
The port is an Edge or Edge no neighbor port.
It is designed to avoid the traffic loop based on the above behavior to adopt dynamic REP configuration changes.
Information About REP
REP Segments
A REP segment is a chain of ports connected to each other and configured with a segment ID. Each segment consists of standard
(nonedge) 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 Trunk Ethernet Flow Point (EFP) interfaces.
The figure below 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.
The segment shown in the figure above 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 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 on any port on a REP segment, REP unblocks all ports to ensure
that connectivity is available through the other gateway.
The segment shown in the figure below is a ring segment, and it has both edge ports located on the same router. With this
configuration, you can create a redundant connection between any two routers in the segment.
REP segments have the following characteristics:
If all ports in a 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, and cause a link failure, all ports forward traffic on all VLANs to
ensure connectivity.
In case of a link failure, alternate ports are unblocked as quickly as possible. When the failed link is 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, which is controlled
by the primary edge port but can occurring at any port in the segment.
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 the REP LSL 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 up, LSL sends
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:
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. Once the neighbor adjacencies are created, the ports negotiate
to determine one blocked port for the segment, which is 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 on a per-VLAN basis, only one hello message is required for all VLANs,
thus reducing the load on the protocol. We recommend that you create VLANs consistently on all switches in a given segment
and configure VLANs on 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 milliseconds (ms) for the local segment.
VLAN Load Balancing
One edge port in a REP segment acts as the primary edge port and 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 using any one of the following ways:
By entering the port ID of the interface. To identify the port ID of a port in the segment, enter the
show interface rep detail command for the port.
By entering 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 indicate the secondary
edge port (offset number -1) and its downstream neighbors.
Note
You configure offset numbers on the primary edge port by identifying a port’s downstream position from the primary (or secondary)
edge port. You cannot enter an offset value of 1 because 1 is the offset number of the primary edge port .
By entering the
preferred keyword to select the port that you previously configured as the preferred alternate port in the
rep segment preferred command.
When the REP segment is complete, all VLANs are blocked. VLAN load balancing can be triggered in one of the following two
ways:
You can manually trigger VLAN load balancing at any time by entering therep preempt segment segment-id command on the router that has the primary edge port.
You can configure a preempt delay time by entering the
rep preempt delay seconds command. After a link failure and recovery, VLAN load balancing begins after the configured preemption time period elapses.
The delay timer restarts if another port fails before the time has elapsed.
Note
A VLAN load balancing does not start working until triggered by either a manual intervention or a link failure and recovery.
When VLAN load balancing is triggered, the primary edge port sends out a message to alert all interfaces in the segment about
the preemption. When the message is received by the secondary edge port, a message is generated in 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 must 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 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 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 failed state. When the alternate port receives the failure notification,
the port 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 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.
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 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 ports to the segment in interface configuration
mode. You should configure two edge ports in the segment, with one as the primary edge port and the other, by default, as
the secondary edge port. A segment has only one primary edge port. If you configure two ports in a segment as primary edge
ports, for example, ports on different switches, REP selects one of them to serve as the primary edge port. You can also optionally
configure where to send segment STCNs and VLAN load balancing. For more information about configuring REP Administrative VLANs,
see the
Configuring the REP Administrative VLAN section.
REP Configuration
Guidelines
Follow these
guidelines when configuring REP:
We recommend that
you begin by configuring one port and then configure 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 selection mechanism.
REP ports must be
Layer 2 IEEE 802.1Q or Trunk EFP ports.
We recommend that
you configure all trunk ports in the segment with the same set of allowed
VLANs.
Be careful when
configuring REP through a Telnet connection. Because REP blocks all VLANs until
another REP interface sends a message to unblock it. You might lose
connectivity to the router if you enable REP in a Telnet session that accesses
the router through the same interface.
You cannot run
REP and STP on the same segment or interface.
If you connect an
STP network to a 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.
If REP is enabled
on two ports on a router, both ports must be either regular segment ports or
edge ports. REP ports follow these rules:
If only one port on a router
is configured in a segment, the port should be an edge port.
If two ports on a router
belong to the same segment, both ports must be edge ports or must be regular
segment ports.
If two ports on a router
belong to the same segment and one is configured as an edge port and the other
as a regular segment port (a misconfiguration), the edge port is treated as a
regular segment port.
REP interfaces
come up in a blocked state and remain in a blocked state until they are safe to
be unblocked. You need to be aware of this status to avoid sudden connection
losses.
REP ports cannot
be configured as one of the following port types:
Switched Port Analyzer
(SPAN) destination port
Tunnel port
Access port
There can be a
maximum of 22 REP segments per router.
REP Support on a Trunk EFP
Resilient Ethernet Protocol (REP) can be configured on Trunk EFP ports at the interface level on Cisco ASR 903 Series Routers.
Trunk EFP ports can have several bridged VLAN services running on them. VLANs can be set to blocking and forwarding state
on a Trunk EFP port. A user must enable REP on a port. By default, REP is disabled on all ports.
REP Configurable
Timers
In a ring
network topology, the Fast Last Link Status (LSL) process detects a neighboring
port and maintains a connection with it. The timer on a port can be configured
within 200-10000 ms to receive LSL frames. If no LSL frames are received from
200 to10000 ms from the neighboring port, the link between routers is
considered as down. The tear-down operation and action is taken to bring up the
link and restore traffic.
In the ring network topology, REP might fail to converge the traffic
within 50 ms. For example, if the topology is made of copper cable, REP might
fail to converge the traffic due to hardware limitations of the copper
interface. In such a scenario, a remote end can take up to 700 ms to detect
shutdown failure of a local port. The REP LSL is enhanced to achieve higher
timer granularity and faster failure detection on the remote side.
The
figure below shows the delay in failure detection due to hardware limitation of
a Copper interface.
SSO Support for REP Fast Hello
When a router crashes, it takes between 3 to 5 seconds for the router to get into active mode and start sending REP Fast
Hello packets. If the value of the age out timer configured by the
lsl age out timer command is less than 3 seconds, the remote end detects a port failure and reconverges. After reconverging, the router sends
out a BPDU with a special type, length, and, value (TLV) to the connected port. The router learns the port’s local and remote
sequence number so that the subsequent REP three-way link integrity check does not fail. The Stateful Switchover (SSO) support
for REP ensures that a Fast Hello packet can be sent from the router before the LSL interval expires.
REP Edge No-Neighbor Support
In a ring network topology, aggregation nodes do not support REP. A REP segment can be created with no-neighbor ports to
achieve convergence of switches. The figure below shows P1 and P2 as Edge No-Neighbor ports in a ring topology. In this configuration
P1 and P2 can block traffic. If there is a failure on any of the links, all the switches with REP configuration converge.
Since P1 and P2 are not edges, they do not support the following tasks:
Perform VLAN load balancing.
Detect topology changes to other segments and the Spanning Tree Protocol (STP).
Choose the port that can preempt.
Display the complete segment topology.
The Edge No-Neighbor support enables defining a new type of edge that has an internal neighbor. In the figure below, P1 and
P2 are configured as Edge No-Neighbor ports rather than intermediate segment ports. These ports inherit properties of edge
ports and overcome the limitations listed above. Thus, the Edge No-Neighbor port (P1 or P2) can send the Multiple Spanning
Tree (MST) protocol, a Topology Change Notification (TCN), and a REP TCN for another segment towards the aggregation switch.
How to Configure REP
Configuring the REP Administrative VLAN
To avoid the delay introduced by relaying messages that are related to link-failures or VLAN-blocking notifications 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 and 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:
There can be only one administrative VLAN on a router and on a segment. However, this is not enforced by the software.
If you do not configure an administrative VLAN, the default is VLAN 1.
If you want to configure REP on an interface, ensure that the REP administrative VLAN is part of the Trunk EFP encapsulation
list.
SUMMARY STEPS
enable
configure terminal
rep admin vlan vlan-id
end
show interface [interface-id]
rep [detail ]
copy running-config startup -config
DETAILED STEPS
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 2
Configures a REP administrative VLAN.
Specify the administrative VLAN. The range is from 2 to 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 interface or port channel ID.
Step 6
copy running-config startup -config
Example:
Router# copy running-config startup-config
(Optional) Save your entries in the router startup configuration file.
Configuring Trunk EFP on an Interface
Before you begin
For the REP operation, you must configure Trunk EFP on an interface. This task is required and must be done before configuring
REP support on a Trunk EFP.
SUMMARY STEPS
enable
configure terminal
interface type number
service
instance trunk service-instance-idethernet
encapsulation dot1q vlan range
rewrite
ingress tag pop 1 symmetric
bridge-domain from-encapsulation
end
DETAILED STEPS
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 type number
Example:
Router(config)# interface GigabitEthernet 0/0/1
Specifies the interface, and enters interface configuration mode.
Enter the interface ID.
Step 4
service
instance trunk service-instance-idethernet
Example:
Router(config-if)# service instance trunk 1 ethernet
Configures a service instance on an interface and enters service instance configuration mode.
For the REP
operation, you must enable REP on each segment interface and identify the
segment ID. This task 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.
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.
(Optional)
edge —Configures
the port as an edge port. Each segment has only two edge ports. Entering the
edge without
the
primary keyword
configures the port as the secondary edge port.
(Optional)
primary —Configures 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 valid. 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.
(Optional)
preferred —Indicates 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 the port a slight edge over equal contenders. The alternate port
is usually a previously failed port.
Step 5
rep stcn {interface type number|
segment id-list |
stp }
Example:
Router(config-if)# rep stcn segment 2-5
(Optional)
Configures the edge port to send STCNs.
Use the
interface type number
keyword-argument pair to designate a physical interface or port channel to
receive STCNs.
Use the
segment id-list
keyword-argument pair to identify one or more segments to receive STCNs. The
range is from 1 to 1024.
Enter
thestp to send
STCNs to STP networks.
Step 6
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-idkeyword-pair 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 type numberrep [detail ] 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 cannot enter
an offset value of 1 to identify an alternate port.
Enter
thepreferred
keyword to select the regular segment port previously identified as the
preferred alternate port for VLAN load balancing.
Enter
thevlan vlan-list
keyword-argument pair to block one VLAN or a range of VLANs.
Enter
thevlan all keyword
to block all VLANs.
Execute this command multiple times to accommodate the desired
set of VLANs. It works as append VLAN to the existing list instead of replacing
an existing one.
Note
Enter this
command only on the REP primary edge port.
Step 7
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 between15 to 300 seconds. The default is manual preemption with
no time delay.
Note
Use this
command only on the REP primary edge port.
Step 8
end
Example:
Router(config-if-srv)# end
Returns to
privileged EXEC mode.
Step 9
show interface type numberrep [detail ]
Example:
Router# show interface Gigabitethernet0/0/1 rep detail
(Optional)
Verifies the REP interface configuration.
Enter the
interface type and number and the optional
detail
keyword, if desired.
Step 10
copy running-config startup-config
Example:
Router# copy running-config startup-config
(Optional)
Saves your entries in the router startup configuration file.
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 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 command to see which port in the segment is the primary edge port.
Before you begin
Be sure that all other segment configurations have been completed before setting the 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.
SUMMARY STEPS
enable
configure terminal
rep preempt segment segment-id
end
show rep topology
DETAILED STEPS
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 preempt segment segment-id
Example:
Router(config)# 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 privileged EXEC mode.
Step 5
show rep topology
Example:
Router# show rep topology
Displays the REP topology information.
Configuring SNMP Traps for REP
You can configure the router to send REP-specific traps to notify the Simple Network Management Protocol (SNMP) server of
link operational status changes and any port role changes.
SUMMARY STEPS
enable
configure terminal
snmp mib rep trap-rate value
end
show running-config
copy running-config startup-config
DETAILED STEPS
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 van be used 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 the REP Configuration
SUMMARY STEPS
enable
show interface [interface-id]
rep [detail ]
show rep topology [segment segment-id] [archive ] [detail ]
DETAILED STEPS
Command or Action
Purpose
Step 1
enable
Example:
Router> enable
Enables privileged EXEC mode.
Enter your password if prompted.
Step 2
show interface [interface-id]
rep [detail ]
Example:
Router# show interface gigabitethernet0/1 rep detail
(Optional) Displays the REP configuration and status for a specified interface.
Enter the physical interface or port channel ID, 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.
Configuring REP Configurable
Timers
Before you begin
For the REP
operation, you must enable REP on each segment interface.
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.
(Optional)
edge —Configures
the port as an edge port. Each segment has only two edge ports. Entering the
edge keyword
without the
primary keyword
configures the port as the secondary edge port.
(Optional)no-neighbor —Configures the segment edge as one
with no external REP neighbor on a port.
(Optional)
primary —Configures 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 valid. 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.
(Optional)
preferred —Indicates 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 the port a slight edge over equal contenders. The alternate port
is usually a previously failed port.
Step 5
rep stcn {interface type number|
segment id-list |
stp }
Example:
Router(config-if)# rep stcn segment 2-5
(Optional)
Configures the edge port to send STCNs.
Use the
interface type number
keyword and arguments pair to designate a physical interface or port channel to
receive STCNs.
Use the
segment id-list
keyword and arguments pair to identify one or more segments to receive STCNs.
The range is from 1 to 1024.
Enter
the
stp
keyword to send STCNs to STP networks.
Step 6
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 VLANs to be blocked on the
alternate port.
Enter the
id port-id
keyword and arguments pair 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 type numberrep [detail ] 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 cannot 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 the
vlan vlan-list
keyword and arguments pair to block one VLAN or a range of VLANs.
Enter
the
vlan all keyword
to block all VLANs.
Execute
this command multiple times to accommodate the desired set of VLANs. It works
as append VLAN to the existing list instead of replacing an existing one.
Note
Enter this
command only on the REP primary edge port.
Step 7
rep lsl-retries number-of-tries
Example:
Router(config-if)# rep lsl-retries 3
Configures the
number of retries permitted by LSL.
Step 8
rep lsl-age-timer timer-value
Example:
Router(config-if)# rep lsl-age-timer 200
Configures the
failure detection time.
The valid range
is from 120 to 10000. We recommend that you configure the minimum
range as 200 for better performance. While a lower value can help
improve performance, any changes to this command must be carefully
evaluated. Lowering the value indiscriminately may destabilize the
system.
Step 9
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 from 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 10
end
Example:
Router(config-if-srv)# end
Returns to
privileged EXEC mode.
Step 11
show interface type numberrep [detail ]
Example:
Router# show interface Gigabitethernet0/0/1 rep detail
(Optional)
Displays the REP interface configuration.
Enter the
interface type and number and the optional
detail
keyword, if desired.
Step 12
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 an Edge No-Neighbor Port
Before you begin
For the REP operation, you must enable REP on each segment interface.
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.
(Optional)
edge -Configures the port as an edge port. Each segment has only two edge ports. Entering
edge without the
primary keyword configures the port as the secondary edge port.
(Optional)no-neighbor -Indicates the segment edge as one with no external REP neighbor on a port.
(Optional)
primary -Configures 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 valid. 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.
(Optional)
preferred -Indicates 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 the port a slight
edge over equal contenders. The alternate port is usually a previously failed port.
Example
Configuration Examples for REP
Configuring the REP Administrative VLAN
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 REP Support on a Trunk EFP
This example shows how to configure REP support on a Trunk EFP. An interface is configured as the primary edge port for segment
1 to send STCNs to segments 2 through 5; the alternate port is configured 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 gigabitethernet0/0/1
Router(config-if)# repsegment 1 edge primary
Router(config-if)# rep stcn segment 2-5
Router(config-if)# rep block port id 0009001818D68700 vlan all
Router(config-if)# rep preempt delay 60
Router(config-if)# service instance trunk 1 ethernet
Router(config-if-srv)# encapsulation dot1q
Router(config-if-srv)# rewrite ingress tag pop 1 symmetric
Router(config-if-srv)# bridge-domain from-encapsulation
Router(config-if-srv)# end
This example shows how to configure the VLAN blocking configuration as shown in the figure below. 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 0/0/1).
Router# configure terminal
Router(config)# interface gigabitethernet0/0/1
Router(config-if)# repsegment 1 edge primary
Router(config-if)# rep block port 4 vlan 100-200
Router(config-if)# end
Setting the Preemption for VLAN Load Balancing
Router>end
Router# configure terminal
Router(config)rep preempt segment 1
Router(config)# end
Configuring SNMP Traps for REP
This example shows how to configure the router to send REP traps at a rate of 10 traps per second:
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.
The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use
these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products
and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.
Feature Information for
Resilient Ethernet Protocol
The following table provides release information about the feature or features described in this module. This table lists
only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise,
subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco
Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 1. Feature Information for
Resilient Ethernet Protocol
Feature
Name
Releases
Feature
Information
REP
Configurable Timers
Cisco IOS XE
Release 3.5.1S
REP Configurable Timers on REP to detect link failures in a
link between routers in a ring topology. In Cisco IOS XE Release 3.5.1S,
support was added for the Cisco ASR 903 Router. In Cisco IOS XE Release 3.11S,
support was added for the Cisco ASR 901 Routers.
The
following sections provide information about this feature:
The Edge No-Neighbor Support on REP enables defining a new type
of edge that has an internal neighbor. In Cisco IOS XE Release 3.5.1S, support
was added for the Cisco ASR 903 Router.
REP can be configured on Trunk Ethernet Flow Point (EFP) ports
at an interface level on ASR 903 Series Routers.
The
following command was introduced by this feature:
service instance
trunk .
SSO Support
for REP Fast Hello
Cisco IOS XE
Release 3.5.1S
SSO Support for REP Fast Hello is provided to ensure that a
Fast Hello packet is sent from an active router before the LSL timeout interval
expires. In Cisco IOS XE Release 3.5.1S, support was added for the Cisco ASR
903 Router. In Cisco IOS XE Release 3.11S, support was added for the Cisco ASR
901 Router.
The
following sections provide information about this feature: