Reference Guide

534 | Link Aggregation Control Protocol
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Monitor and Debugging LACP
The system log (syslog) records faulty LACP actions.
To debug LACP, use the following command:
Shared LAG State Tracking
Shared LAG State Tracking provides the flexibility to bring down a port channel (LAG) based on the
operational state of another LAG. At any time, only two LAGs can be a part of a group such that the fate
(status) of one LAG depends on the other LAG.
In Figure 27-1, line-rate traffic from R1 destined for R4 follows the lowest-cost route via R2, as shown.
Traffic is equally distributed between LAGs 1 and 2. If LAG 1 fails, all traffic from R1 to R4 flows across
LAG 2 only. This condition over-subscribes the link, and packets are dropped.
Figure 27-1. LAGs using ECMP without Shared LAG State Tracking
To avoid packet loss, traffic must be re-directed through the next lowest-cost link (R3 to R4). FTOS has
the ability to bring LAG 2 down in the event that LAG 1 fails, so that traffic can be re-directed, as
described. This is what is meant by Shared LAG State Tracking. To achieve this functionality, you must
group LAG 1 and LAG 2 into a single entity, called a failover group.
Command Syntax Command Mode Purpose
[no] debug lacp [config | events | pdu [in | out
| [interface [in | out]]]]
EXEC Debug LACP, including configuration and events.
Po 1
Po 2
f C0049
R1
R2 R3
R4
Po 1 failure
Po 2 over-subscribed