The previous sections described operation principle of several redundancy mechanisms available in context of VPLS service. All of them rely on MAC flush message as a tool to propagate topology change in a context of the specific VPLS. This section aims to summarize basic rules for generation and processing of these messages.
As described on respective sections, the 7210 SAS supports 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 requests clearing of all FDB entries which 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 message requests clearing all FDB entries learned from originating PE. This means that this message has exactly other effect then flush-all-but-mine message. This type is not included in 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 focuses on summarizing actions taken on reception and conditions individual messages are generated.
Upon reception of MAC flush messages (regardless the type) SR-Series PE takes following actions:
Clears FDB entries of all indicated VPLS services conforming the definition.
Propagates the message (preserving the type) to all LDP peers, if ‟propagate-mac-flush” flag is enabled at corresponding VPLS level.
The flush-all-but-mine message is generated under following conditions:
The flush-all-but-mine message is received from LDP peer and propagate-mac-flush flag is enabled. The message is sent to all LDP peers in the context of VPLS service it was received in.
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 specific STP instance (based on mVPLS definition). The message is sent only to LDP peers which are not part of STP domain, which means corresponding spoke and mesh SDPs are not part of mVPLS.
Flush-all-but-mine message is generated when switch over between spoke SDPs of the same endpoint occurs. The message is sent to LDP peer connected through newly active spoke-SDP.
The flush-mine message is generated under following conditions:
The flush-mine message is received from LDP peer and propagate-mac-flush flag is enabled. The message is sent to all LDP peers in the context of 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 send-flush-on-failure flag is enabled in the context of the specific VPLS service. The message is sent to all LDP peers connected in the context of the specific VPLS service. Note, that enabling send-flush-on-failure the flag is blocked in VPLS service managed by mVPLS. This is to prevent both messages from being sent at the same time.
The flush-mine message is generated when an MC-LAG 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 specific VPLS service.