Hi @nwekechampion
Most everyone is familiar with BFD (RFCs 5880/5881/5882), which I am sure you are as well, as a liveness checking mechanism (capability to forward bi-directionally) that can use IPv4 or IPv6 for source and destination addresses of the BFD session, with the session working over a single link with a single hop. When BFD detects that forwarding has failed, it notifies a "client" process that the path is down, so that the client can take some action. If the client is a routing protocol (BGP, OSPF, etc), the protocol can then initiate a reconvergence of its RIB. Since the single-link, single-hop requirement does not work for many networking use-cases, BFD has been extended to include operation over other path types, including LAG bundles.
With BFD over Logical Bundle (BLB) , BFD treats the LAG bundle (or Etherchannel, or whatever the vendor calls it) as a single logical link, even though there can be many physical links in the bundle. The BFD session is up as long as the LAG bundle is up, and the client is still typically a routing protocol. It does not detect failure of individual links in the bundle, just whether the bundle is up.
BFD can also be used as an alternative to LACP to quickly detect failures in individual link members of the LAG bundle, by running a separate BFD session over every link in the bundle. The IETF standardized this as RFC 7130 and is often called "micro BFD" in the industry, but Cisco calls it BFD over Bundle (BoB). In Cisco's case, the client is the bundle-manager process, rather than a routing protocol, and when notified by BFD of a path failure the bundle-manager can remove the failed link from the bundle (same as LACP would do, except that BFD can be faster).
Good references on BFD, BLB, and BoB, but with an IOS-XR orientation:
https://community.cisco.com/t5/service-providers-blogs/bfd-over-logical-bundle-blb-implementation-on-ncs5500-platforms/ba-p/3309345
https://community.cisco.com/t5/service-providers-knowledge-base/bfd-support-on-cisco-asr9000/ta-p/3153191
https://xrdocs.io/ncs5500/tutorials/coexistence-between-bfd-over-bundle-and-bfd-over-logical-bundle/
With BoB, the BFD session on every link is still encapsulated in IP/UDP so there still must be IP source and destination addresses for the session (unlike LACP which is encap'ed directly in its Ethertype). The individual sessions on each link in a bundle are identified by discriminators rather than IP addresses, so each individual session does not need to have its own IP addresses. Being able to (re)use an IPv4 loopback address as the source and destination for BoB sessions can then save hundreds, or even thousands, of IPv4 addresses across your network if you have a large network where all elements are interconnected with LAG bundles.
Disclaimers: I am long in CSCO. Bad answers are my own fault as they are not AI generated.
