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Publicado: 3 de abril de 2011
CH A P T E R
17
Configuring Resilient Ethernet Protocol
This chapter describes how to use Resilient Ethernet Protocol (REP) on the Cisco ME 3400 Ethernet Access switch. REP is a Cisco proprietary protocol that provides an alternative to Spanning Tree Protocol (STP) to control network loops, handle link failures, and improve convergence time. REP controls a group of ports connected in asegment, 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 switch supports REP only when it is running the metro IP access or metro access image. This chapter includes these sections:
• • •
Understanding REP, page 17-1 Configuring REP, page17-6 Monitoring REP, page 17-12
Understanding REP
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 switch 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 gothrough 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 17-1 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. Whenthere is a failure in the network, as shown in the diagram on the right, the blocked port returns to the forwarding state to minimize network disruption.
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide OL-9639-05
17-1
Chapter 17 Understanding REP
Configuring Resilient Ethernet Protocol
Figure 17-1
REP Open Segments
E1
Edge port Blocked port Link failureE1
E2
E1
E2
The segment shown in Figure 17-1 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 switches inside the segment have two possible connections to the rest of the network through the edge ports, but only one connection isaccessible at any time. If a failure causes a host to be unable to access its usual gateway, REP unblocks all ports to ensure that connectivity is available through the other gateway. The segment shown in Figure 17-2, 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 cancreate a redundant connection between any two switches in the segment.
Figure 17-2 REP Ring Segment
E1
E2
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 oneor 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.
• •
Cisco ME 3400 Ethernet Access Switch SoftwareConfiguration Guide
17-2
201889
201888
OL-9639-05
Chapter 17
Configuring Resilient Ethernet Protocol Understanding REP
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 these limitations:
• • •
You must configure each segment port;...
17
Configuring Resilient Ethernet Protocol
This chapter describes how to use Resilient Ethernet Protocol (REP) on the Cisco ME 3400 Ethernet Access switch. REP is a Cisco proprietary protocol that provides an alternative to Spanning Tree Protocol (STP) to control network loops, handle link failures, and improve convergence time. REP controls a group of ports connected in asegment, 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 switch supports REP only when it is running the metro IP access or metro access image. This chapter includes these sections:
• • •
Understanding REP, page 17-1 Configuring REP, page17-6 Monitoring REP, page 17-12
Understanding REP
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 switch 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 gothrough 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 17-1 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. Whenthere is a failure in the network, as shown in the diagram on the right, the blocked port returns to the forwarding state to minimize network disruption.
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide OL-9639-05
17-1
Chapter 17 Understanding REP
Configuring Resilient Ethernet Protocol
Figure 17-1
REP Open Segments
E1
Edge port Blocked port Link failureE1
E2
E1
E2
The segment shown in Figure 17-1 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 switches inside the segment have two possible connections to the rest of the network through the edge ports, but only one connection isaccessible at any time. If a failure causes a host to be unable to access its usual gateway, REP unblocks all ports to ensure that connectivity is available through the other gateway. The segment shown in Figure 17-2, 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 cancreate a redundant connection between any two switches in the segment.
Figure 17-2 REP Ring Segment
E1
E2
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 oneor 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.
• •
Cisco ME 3400 Ethernet Access Switch SoftwareConfiguration Guide
17-2
201889
201888
OL-9639-05
Chapter 17
Configuring Resilient Ethernet Protocol Understanding REP
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 these limitations:
• • •
You must configure each segment port;...
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