Figure 3-17 ZESS protection mechanism
3.7.4.3 Intelligent dual-homed ZESR+
When metro core network uplinks backbone network, one switch has two uplink ports
connecting two BRAS or SR, thus ZESS provides dual-uplink protection. Although the
connection has uplink and SR or BRAS protection, there is single-point fault risk from
uplink to BRAS or SR. For consideration of security in the actual networking, 2 uplink
ports connected to the same SR or BRAS are located in 2 switches, and the downlink still
uses the ZESR ring. Two uplink switches adopts ZESS and two switches remain the
heartbeat hello. When port 4 goes wrong, the traffic switches to port 5; when a fault
occurs to port 5, the traffic goes to the right switch. Thus lower-layer link fulfills the ring
protection and traffic load balance and backup. The working principle is shown as Figure
3-18.
Figure 3-18 ZESR+ working principle
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