Reference Guide

Setting the LACP Long Timeout
PDUs are exchanged between port channel (LAG) interfaces to maintain LACP sessions.
PDUs are transmitted at either a slow or fast transmission rate, depending upon the LACP timeout value. The timeout value is
the amount of time that a LAG interface waits for a PDU from the remote system before bringing the LACP session down. The
default timeout value is 1 second. You can configure the default timeout value to be 30 seconds. Invoking the longer timeout
might prevent the LAG from flapping if the remote system is up but temporarily unable to transmit PDUs due to a system
interruption.
NOTE: The 30-second timeout is available for dynamic LAG interfaces only. You can enter the lacp long-timeout
command for static LAGs, but it has no effect.
To configure LACP long timeout, use the following command.
● Set the LACP timeout value to 30 seconds.
CONFIG-INT-PO mode
lacp long-timeout
Dell(conf)# interface port-channel 32
Dell(conf-if-po-32)#no shutdown
Dell(conf-if-po-32)#switchport
Dell(conf-if-po-32)#lacp long-timeout
Dell(conf-if-po-32)#end
Dell# show lacp 32
Port-channel 32 admin up, oper up, mode lacp
Actor System ID: Priority 32768, Address 0001.e800.a12b
Partner System ID: Priority 32768, Address 0001.e801.45a5
Actor Admin Key 1, Oper Key 1, Partner Oper Key 1
LACP LAG 1 is an aggregatable link
A - Active LACP, B - Passive LACP, C - Short Timeout, D - Long Timeout
E - Aggregatable Link, F - Individual Link, G - IN_SYNC, H - OUT_OF_SYNC
I - Collection enabled, J - Collection disabled, K - Distribution enabled L -
Distribution disabled,
M - Partner Defaulted, N - Partner Non-defaulted, O - Receiver is in expired
state,
P - Receiver is not in expired state
Port Te 10/6 is enabled, LACP is enabled and mode is lacp
Actor Admin: State ADEHJLMP Key 1 Priority 128
To view the PDU exchanges and the timeout value, use the debug lacp command. For more information, refer to Monitoring
and Debugging LACP.
Monitoring and Debugging LACP
The system log (syslog) records faulty LACP actions.
To debug LACP, use the following command.
● Debug LACP, including configuration and events.
EXEC mode
[no] debug lacp [config | events | pdu [in | out | [interface [in | out]]]]
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.
As shown in the following illustration, the line-rate traffic from R1 destined for R4 follows the lowest-cost route via R2. 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.
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Link Aggregation Control Protocol (LACP)