Information About Bidirectional Forwarding Detection on Link Aggregation Group Bundle
The Bidirectional Forwarding Detection (BFD) enhancement to address per-link efficiency feature enables users to configure individual BFD sessions on each Link Aggregation Group (LAG) member interface. With this enhancement BFD sessions run on each member link of the port-channel. BFD sessions running on member links of the port-channel are called as micro BFD sessions. Micro BFD sessions are supported for both LACP and non-LACP based-port channels. If BFD detects a fault in the bidirectional path between two forwarding engines that includes interfaces and data links, the member link is removed from the forwarding table. This mechanism delivers faster failure detection as the BFD sessions are created on individual port-channel interface. Users can configure BFD over main port-channel interface, that will monitor the bandwidth consumption of LAG by using a micro BFD session for each member. If any member port goes down the port is removed from the forwarding table and this prevents black holing of traffic on that member. Micro BFD works only when it is configured on all the members of port-channel. The logical BFD session takes less aggressive timers than the BFD on LAG sessions, whether it is configured on port-channel or port-channel sub-interfaces.
LAG combines multiple physical links into a single logical link that helps in providing higher bandwidth and better resiliency. If the physical member links fails, the aggregate logical link can continue to forward traffic over the remaining operational physical member links.
With the support of micro BFD feature, port channel manager considers the state of micro BFD sessions to determine the state of the port channel interface. Port channel implementation provides minimum links (lacp min-links) configuration to ensure bandwidth availability by making a port channel usable or unusable based on whether configured number of ports are available or not. The detection of micro BFD happens only when Link Aggregation Control Protocol (LACP) in COLLECTIING_DISTRIBUTION is in active state. Maximum member port supported for LACP mode per port-channel varies from one platform to another. For example, ASR 1000 supports 14 port-channels.
The goal of micro BFD sessions are:
Run BFD session over each LAG member link.
Verify link continuity for each member link.
Allow BFD to control the LAG member link to be part of the L2 load-balancing table of the LAG interface in the presence or absence of LACP.