Specific ‟failure scenarios” in the network can trigger effects. The following figure shows some of these scenarios.
If an individual VPLS service is shutdown in PE1 (the example is also valid for PE2), the corresponding LAG SAP goes operationally down. This event triggers the withdrawal of the AD per-EVI route for that SAP. PE3 removes PE1 from its list of aliased next-hops, and PE2 takes over as DF (if it was not the DF already). However, this does not prevent the network from black-holing the traffic that CE2 ‟hashes” to the link to PE1. Because traffic sent from CE2 to PE2 or traffic from the rest of the CEs to CE2 is unaffected, the situation is not easily detected on the CE.
The same result occurs if the ES SAP is administratively shutdown instead of the service.
When the bgp-evpn mpls shutdown command is executed, the SAP associated with the ES goes operationally down (StandbyforMHprotocol). If no other SAPs or SDP-bindings are configured in the service, the service also goes operationally down. However, if other SAPs or SDP-bindings are present, the service remains operationally up.