The services implementation allows for manually provisioned and auto-discovered pseudowire (SDP bindings) to coexist in the same VPLS instance (for example, both FEC128 and FEC 129 are supported). This allows for gradual introduction of auto-discovery into an existing VPLS deployment.
As FEC 128 and 129 represent different addressing schemes, it is important to ensure that only one is used at any time between the same two VPLS instances. Otherwise, both pseudowires may become active causing a loop that may adversely impact the correct functioning of the service. It is recommended that FEC128 pseudowire be disabled as soon as the FEC129 addressing scheme is introduced in a portion of the network. Alternatively, RSTP may be used during the migration as a safety mechanism to provide additional protection against operational errors.