The previous sections described operating principles of several redundancy mechanisms available in the context of VPLS service. All of them rely on MAC flush messages as a tool to propagate topology change in a context of the specified VPLS. This section summarizes basic rules for generation and processing of these messages.
As described in respective sections, the 7450 ESS, 7750 SR, and 7950 XRS support two types of MAC flush message: flush-all-but-mine and flush-mine. The main difference between these messages is the type of action they signal. Flush-all-but-mine messages request clearing of all FDB entries that were learned from all other LDP peers except the originating PE. This type is also defined by RFC 4762 as an LDP MAC address withdrawal with an empty MAC address list.
Flush-all-mine messages request clearing all FDB entries learned from the originating PE. This means that this message has the opposite effect of the flush-all-but-mine message. This type is not included in the RFC 4762 definition and it is implemented using vendor-specific TLV.
The advantages and disadvantages of the individual types should be apparent from examples in the previous section. The description here summarizes actions taken on reception and the conditions under which individual messages are generated.
Upon reception of MAC flush messages (regardless of the type), an SR-series PE takes the following actions:
Clears FDB entries of all indicated VPLS services conforming to the definition.
Propagates the message (preserving the type) to all LDP peers, if the propagate-mac-flush flag is enabled at the corresponding VPLS level.
The flush-all-but-mine message is generated under the following conditions:
The flush-all-but-mine message is received from the LDP peer and the propagate-mac-flush flag is enabled. The message is sent to all LDP peers in the context of the VPLS service it was received.
The TCN message in a context of STP instance is received. The flush-all-but-mine message is sent to all LDP peers connected with spoke and mesh SDPs in a context of VPLS service controlled by the specified STP instance (based on M-VPLS definition). If all LDP peers are in the STP domain, that is, the M-VPLS and the uVPLS (user VPLS) both have the same topology, the router does not send any flush-all-but-mine message. If the router has uVPLS LDP peers outside the STP domain, the router sends flush-all-but-mine messages to all its uVPLS peers.
The 7750 SR does not send a withdrawal if the M-VPLS does not contain a mesh SDP. A mesh SDP must be configured in the M-VPLS to send withdrawals.
The flush-all-but-mine message is generated when switchover between spoke-SDPs of the same endpoint occurs. The message is sent to the LDP peer connected through the newly active spoke-SDP.
The flush-mine message is generated under the following conditions:
The flush-mine message is received from the LDP peer and the propagate-mac-flush flag is enabled. The message is sent to all LDP peers in the context of the VPLS service it was received.
The flush-mine message is generated when a SAP or SDP transitions from operationally up to an operationally down state and the send-flush-on-failure flag is enabled in the context of the specified VPLS service. The message is sent to all LDP peers connected in the context of the specified VPLS service. The send-flush-on-failure flag is blocked in M-VPLS and is only allowed to be configured in a VPLS service managed by M-VPLS. This is to prevent both messages being sent at the same time.
The flush-mine message is generated when an MC-LAG SAP or MC-APS SAP transitions from an operationally up state to an operationally down state. The message is sent to all LDP peers connected in the context of the specified VPLS service.
The flush-mine message is generated when an MC-Ring SAP transitions from operationally up to an operationally down state or when MC-Ring SAP transitions to slave state. The message is sent to all LDP peers connected in the context of the specified VPLS service.