Precautions for the configuration of multicast BFD sessions on S series switches

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For S series switches, the packets sent by multicast BFD are untagged.
When a BFD interface receives a tagged BFD packet, the BFD module checks whether the VLAN ID of the BFD packet is the same as the default VLAN ID on the interface. If not, the BFD module discards the packet.
To configure multicast BFD on an interface, run the port default vlan command to specify the default VLAN of the interface.

Other related questions:
What are the precautions for configuring multicast BFD
The BFD packets sent in multicast mode are untagged. When a port configured with multicast BFD receives tagged packets, it checks the tag of the packets. If the tag is different from the port's default VLAN ID, the port discards the packets. To configure multicast BFD on an interface, run the port default vlan command to specify the default VLAN of the 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.

For S series switches, whether the BFD echo function supports multi-hop BFD sessions
For S series switches (except S1700), BFD echo is applicable only to single-hop BFD sessions. Between two directly connected switches, one switch supports BFD, but the other does not support BFD and supports only forwarding at the network layer. To rapidly detect forwarding failures between the two switches, configure the BFD echo function on the BFD-supported device. The BFD-supported switch sends an Echo Request to the remote device, and the remote device sends the Echo Request back along the same path to detect the connectivity of the forwarding link.

What precautions should I take when using multicast addresses on an S series switches
Class D IP addresses are used as multicast addresses, ranging from 224.0.0.0 to 239.255.255.255. Not all class D IP addresses can be allocated randomly. Similar to unicast addresses, many reserved addresses exist. The reserved addresses are classified into the following types: - Permanent multicast group addresses ranging from 224.0.0.0 to 224.0.0.255 are network protocol addresses allocated by IANA to the local network. When packets are sent, the TTL of the packets is 1. Therefore, the router does not forward packets from the local network segment. For example, base addresses (reserved group addresses) are multicast group addresses. 224.0.0.1: indicates all the hosts and routers joining multicast groups on a subnet. 224.0.0.2: indicates all the routers joining multicast groups on a subnet. 224.0.0.4: indicates Distance Vector Multicast Routing Protocol (DVMRP) routers. 224.0.0.13: indicates PIMv2 routers. 224.0.0.22: indicates IGMPv3 routers. - User group addresses ranging from 224.0.1.0 to 238.255.255.255 are valid on the entire network and can be used. These addresses include the following special reserved addresses: 224.0.1.0 to 224.0.1.255: not local addresses. When packets are sent from these addresses, the TTL is greater than 1. 224.0.1.1: indicates the NTP address. 224.0.1.6: indicates the NSS address. 224.0.1.78: indicates Tibco multicast 1. 232/8: indicates the SSM group address. 233/8: indicates the GLOP group address. - Local management group addresses ranging from 239.0.0.0 to 239.255.255.255 are valid in the local management domain only. They are private addresses and cannot be used on public networks.

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