Introduction to Resilient Ethernet Protocol- REP

Today I am going to talk about the protocol name as Resilient Ethernet Protocol- REP. Resilient Ethernet Protocol- REP is a cisco Propriety protocol and generally used in the ring topology. Many of you already knew about the Resilient Ethernet Protocol- REP but some of you just try to understand what is the purpose of the Resilient Ethernet Protocol- REP. Let me talk about Resilient Ethernet Protocol- REP.

So if you talk about REP, REP is a protocol used in order to replace the Spanning Tree Protocol (STP) in some specific Layer 2 network designs. The most current STP specification is Multiple Spanning Trees (MST), defined in 802.1Q-2005.

REP is a distributed and secure control plane protocol that does not rely on a master node monitoring the health of the ring. REP provides an additional layer of security, which protects the reliability and availability of the REP segment with the use of a 9-byte word generated by the alternate port and that is unique to that REP segment. 

The primary edge port is responsible only for initiating topology collection. Failure can be detected locally either through LOS or loss of neighbor adjacency. Any REP port can initiate a switchover as long as it has acquired a secure key to unblock the alternate port. 

Fig 1.1- REP Protocol Sample Topology

Well here in the case of the REP, it uses a segment as a minimal network building block. Now i knew the question is what is the segment here. A segment is simply a collection of ports chained together. Only two ports can belong to a given segment on a bridge, and each segment port can have a maximum of one external neighbor. The definition of the segment is entirely achieved by user configuration. The segment is terminated by two edge ports that are also determined by the user

Let me talk about the properties of the REP protocol: 

• If we talk about the all the ports in the segment, It should be online and operational, a single one of them logically blocks traffic for each VLAN.
• If at least one port in the segment is not operational for any reason, all the other operational ports forward for all the VLANs.
• In case of link failure, unblocking all the operational ports that remain is achieved as fast as possible. Similarly, when the last failed port becomes operational again, electing one logically-blocked port per VLAN should introduce as little disruption in the network as possible.

In next Article I will take through the configuration section of REP which includes the basic configuration and the topology.