Which interfaces can be configured with BFD sessions

3

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.

Other related questions:
Which interfaces support BFD sessions on the AR router
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: 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, Ethernet sub-interfaces (including Dot1q sub-interfaces and QinQ 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 and Layer 3 Eth-Trunks. Note: Multicast BFD sessions cannot be established on Layer 2 Ethernet interfaces, Layer 2 Eth-Trunks, or Layer 3 Eth-Trunks of AR120, AR150, AR160, AR200 and 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.

Is the BFD Echo function applicable to multi-hop BFD sessions
The BFD Echo function is only applicable to single-hop BFD sessions. For two directly connected devices, one device supports BFD, and the other device supports only forwarding at the network layer and does not support BFD. To rapidly detect forwarding failures between the two devices, configure the BFD Echo function on the BFD-supporting device. The BFD-supporting device sends an Echo Request packet to the remote device, and the remote device sends the Echo Request packet back along the same path to detect the connectivity of the forwarding link.

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