When interfaces used to track BFD sessions are configured on an S9300, and the WTR time is set, why does BFD flapping occur sometimes

18

S9300 switches have LE0MFSUA installed on the MPU. In V100R002, when a BFD session becomes Up, the blocked port is unblocked. When the WTR time is set and the BFD session state changes from Down to Up, BFD sends a notification to the upper-layer application only after the WTR time expires. In this case, the port's blocking state is canceled until the WTR timer times out. The blocked port, however, cannot send packets, causing the BFD session to become Down again. BFD flapping occurs. This problem is solved in V100R003 and later versions.

Other related questions:
Which interfaces can be configured with BFD sessions
In V200R001C00, only Ethernet interfaces support BFD sessions. In V200R001C01 and later versions, the following interfaces support common BFD sessions: -Physical interfaces: Layer 3 Ethernet interfaces, serial interfaces (including synchronous SA interfaces, E1/T1 interfaces, CE1/CT1/PRI interfaces, CE3 interfaces, and CPOS interfaces), POS interfaces, ATM interfaces (including ADSL interfaces, VDSL interfaces, E1-IMA interfaces, and G.SHDSL interfaces). -Logical interfaces: Ethernet sub-interfaces (including Dot1q sub-interfaces and QinQ sub-interfaces), dialer interfaces, VLANIF interfaces, Layer 3 Eth-Trunk interfaces, IP-Trunk interfaces, MP-Group interfaces, MFR interfaces, IMA-group interfaces, serial sub-interfaces, channelized serial sub-interfaces, IMA-group sub-interfaces, POS sub-interfaces, ATM sub-interfaces, MFR sub-interfaces, and Eth-Trunk sub-interfaces (Dot1q sub-interfaces). NOTE: When a physical Ethernet interface consists of multiple sub-interfaces, a BFD session can be established on the physical Ethernet interface or each sub-interface. In V200R001C01 and later versions, the following interfaces support multicast BFD sessions: -Physical interfaces: Layer 2 and Layer 3 Ethernet interfaces -Logical interfaces: Layer 2 Eth-Trunk interfaces and Layer 3 Eth-Trunk interfaces NOTE: -Multicast BFD sessions cannot be established on Layer 2 Ethernet interfaces, Layer 2 Eth-Trunk interfaces, or Layer 3 Eth-Trunk interfaces of AR120&AR150&AR160&AR200 or AR1200's SRUs. -When a physical Ethernet interface consists of multiple sub-interfaces, a BFD session can be established on the physical Ethernet interface or each sub-interface.

Why can association between BFD session status and interface status on S series switches be used only on multicast BFD sessions
For S series switches, a multicast BFD session uses multicast packets and is not affected by the protocol status on an interface. When the BFD session goes Down and the protocol status on the interface changes to BFDSatusDown, multicast BFD packets can still be sent. After the link recovers, the multicast BFD session becomes Up after negotiation. As a result, the interface is unlocked and becomes Up. Unicast packets, however, cannot be sent or received after the protocol status on the interface goes Down, which causes deadlock.

How do I distinguish a single-hop BFD session and a multi-hop BFD session
Static BFD sessions: When the session is created for the first time, a single-hop BFD session is bound to a local interface while a multi-hop session is not. Dynamic BFD sessions: Query the routes to determine whether a BFD session is a single-hop session or a multi-hop session. BFD for Internal Border Gateway Protocol (IBGP) sessions are multi-hop sessions.

If you have more questions, you can seek help from following ways:
To iKnow To Live Chat
Scroll to top