When the AR router is directly connected to a PC, does the AR support one-arm Echo sessions

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When the AR router is directly connected to a PC, the AR supports one-arm Echo sessions. The PC does not support IP packet forwarding; therefore, BFD Echo packets cannot be forwarded.

Other related questions:
Whether the one-arm BFD echo function supports multi-hop on the AR
The one-arm 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 one-arm 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.

Can a single-hop BFD session be established when a router directly connects to a PC
No, a single-hop BFD session cannot be established in this situation. This is because the PC does not have the IP packet forwarding capability and cannot forward BFD Echo packets.

Can the RIP protocol on an AR router associate with a one-armed BFD
The RIP protocol on an AR router can associate with a one-armed BFD. For details about the configuration, see the following URL: Example for Configuring One-Arm Static BFD for RIP.

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.

The reason why a device directly connected to an AR router cannot be pinged or the IP address of the device that is obtained over DHCP is returned slowly
In Layer 2 networks, STP can solve network loop problems. By default, this function is enabled on an AR router. If the AR router is used as a user access device (the WAN interface of the router is connected to the Internet, and the LAN interface is connected to an intranet), there is no risk of loop generally. In this case, you are advised to run the stp disable command to disable STP and avoid interface blockage due to the enabled STP function or network flapping due to STP convergence. For example, a device directly connected to an AR router cannot be pinged or the IP address of the device that is obtained over DHCP is returned slowly.

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