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AR500, AR510, and AR530 V200R007 CLI-based Configuration Guide - Ethernet Switching

This document describes the configuration of Ethernet services, including configuring transparent bridge, MAC table, link aggregation, VLANs, STP/RSTP/MSTP, and so on.The document provides the configuration procedures and configuration examples to illustrate the service configuration methods and application scenario.
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Principles of SEP

Principles of SEP

SEP is a ring network protocol dedicated to the Ethernet link layer. A SEP segment is the basic unit for SEP. Only two interfaces on a switching device can be added to the same SEP segment.

To prevent loops in a SEP segment, a ring protection mechanism is used to selectively block interfaces to eliminate Ethernet redundant links. When a link on a ring network fails, the device running SEP immediately unblocks the interface and performs link switching to restore communication between nodes.

Figure 13-1 shows a typical SEP application. CE1 is connected to Network Provider Edges (NPEs) through a semi-ring formed by Routers. A VRRP group is deployed on the NPEs. Initially, NPE1 serves as the master and NPE2 as backup to NPE1. When the link between NPE1 and Router5 or a node on the link becomes faulty, NPE1 becomes the backup to NPE2, which then becomes the master. The following situations occur depending on whether SEP is deployed. The following assumes that the link between Router1 and Router5 becomes faulty.
  • If SEP is not deployed on the semi-ring, CE1 traffic is still transmitted along the original path, but NPE1 does not forward traffic, causing traffic interruption.

  • If SEP is deployed on the semi-ring, the blocked interface on Router5 is unblocked, enters the Forwarding state, and sends link state advertisements (LSAs) to instruct other nodes on the SEP segment to update their LSA databases. Then CE1 traffic is transmitted along backup link Router5->Router2->Router4->NPE2, ensuring uninterrupted traffic transmission.

Figure 13-1  Schematic diagram for SEP

In common SEP networking, a physical ring can be configured with only one SEP segment in which only one interface can be blocked. If an interface in a complete SEP segment is blocked, all service data is transmitted only along the path where the primary edge interface is located. The path where the secondary edge interface is located remains idle, wasting bandwidth.

SEP multi-instance is used to improve bandwidth efficiency and implement traffic load balancing. SEP multi-instance allows two SEP segments to be configured on a physical ring. Each SEP segment independently detects the completeness of the physical ring, blocks or unblocks interfaces without affecting the other.

For details about SEP multi-instance, see SEP Implementation Mechanisms.

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Updated: 2019-05-25

Document ID: EDOC1000097279

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