BFD in a Stacking System
The configuration of a BFD session
occurs on the unit where the TX port, or next hop, resides. The TX port is known
once the
ARP, or the next hop in the case of a multihop BFD session, is resolved.
BFD operates in a stacking system in the following manner:
- An application or protocol notifies BFD about the initiation of a session.
- The appropriate MAC address and physical port information is gathered.
- An IPC message is sent from the active unit to the remote unit to configure the BFD session.
- Upon receipt of the IPC message, the standby unit stores the session locally.
- If the TX port is a local unit port, the source host IP programming is moved from the ALPM to the L3_Entry table. The BFD session is then configured in the micro-controller.
- The BFD enable bit is then set in the respective L3_Entry table and the Layer 2 entry pointing to the session my_discriminator value in the local unit is also programmed.
The active unit can program the BFD sessions on any remote unit. A BFD session is programmed only on the micro-controller of the remote unit ,and BFD packet exchange with the peer occurs from the micro-controller of the remote unit.
Any state change for the BFD session in the micro-controller invokes the software callback within the unit. If this unit is not the active unit, the standby unit relays the event to the active unit through IPC messages. On receipt of such a notification, the active unit updates the state locally and notifies all applications.