CHAPTER13

Ethernet Ring Protection
•EthernetRing Protection on page 145
•EthernetRing Protection Using Ring Instances for LoadBalancing on page 147
•Example:Configuring Ethernet Ring Protection forMX Series Routers on page 148
•Example:Configuring Load Balancing Within Ethernet Ring Protectionfor MX Series
Routerson page 154
•Example:ViewingEthernet Ring Protection Status—NormalRing Operation on page 171
•Example:Viewing Ethernet Ring ProtectionStatus—Ring Failure Conditionon page 172

EthernetRing Protection

Linkfailure is often an unavoidable part of networking.However, there are methods of
improvingthe reliability of a router or bridge network evenwhen link failures occur. For
example,SONET/SDHseal-healing rings are frequentlyused to add a level of robustness
torouter networks. This ring protectionswitching is now extended to Ethernet links. You
canconfigure Ethernet ring protection for a series of twoor more systems so that if one
linkfails, traffic is rerouted around the failureon the ring.
Thebasic idea of Ethernet ring protection is to use one specific link toprotect the whole
ring.This special link is the ring protection link (RPL). When all links are up and running,
theRPL blocks traffic and remains idle. The RPL itselfis controlled by the designated
RPLowner node. There is only one RPL owner node on the ring and the RPL owner node
isresponsiblefor blocking the RPL interface under normal operatingconditions. However,
ifa link failure occurs on the ring, the RPL owner node is responsiblefor unblocking the
RPLinterface and protection–switchingthe traffic on the alternate path aroundthe ring.
AnEthernet ring automaticprotection switching (R-APS) messagingprotocol coordinates
theprotection activities of all nodes on the ring. The APS blockstraffic over the failed
linkand unblocks traffic over the RPL.
Whenthe failed link is repaired, the trafficreverts to its normal pattern. That is, the RPL
ownerblocks the RPL link and unblocks traffic overthe cleared link.
Twoor morenodes form a ring. Links between the nodes form a chain, with the last node
alsoconnecting the first. Every ring node therefore hastwo ports related to the ring, one
ineach direction. In this chapter, these directionsare referred to as east and west.
145Copyright© 2010, Juniper Networks,Inc.