Reference Guide

When the switch starts receiving LACP PDU, OS10 ungroups the statically added member port from LACP port-channel and resumes with
normal LACP functionality..
When you enable LACP fallback, the port that comes up is selected based on the following:
• LACP port priority conguration allows deterministic port allocation. The port with the least priority is placed in the active state when a
port-channel is in LACP fallback mode.
• If all the ports in a port-channel have same port priority, the switch internally compares the interface names by base name, module
number, port number, and then selects the lowest one to be active. For example, Ethernet 1 is less than Ethernet 2 and hence Ethernet
1 becomes active.
• In a VLT network, if the interface name is the same on both the VLT peers, then the port in switch with lower system MAC address
becomes active.
Limitations
• OS10 switches cannot be a PXE client irrespective of whether it acts as a VLT peer or ToR switch.
• If you are conguring LACP fallback in a VLT domain, congure lacp fallback commands in both the VLT peers.
• If you do not enable LACP fallback in one of the VLT peers, or congure dierent time-out values in the peers, then the switch might
behave dierently.
• The LACP fallback feature adds or groups a member port to the port channel only when the switch does not receive LACP PDUs from
the peer, to make the link connected to the PXE client device as operational. As PXE clients handle untagged DHCP request, you need
to congure the LACP fallback only on an untagged VLAN to reach the DHCP/PXE server.
• After the LACP fallback election, if a port with lower priority port is congured to be part of the same port-channel, it would trigger re-
election.
Congure LACP fallback
1 Enable LACP fallback with the lacp fallback enable in port-channel INTERFACE mode.
2 Set a timer for receiving LACP PDUs using lacp fallback timeout timer-value in port-channel INTERFACE mode.
Example conguration
OS10# configure terminal
OS10(config)# interface port-channel 1
OS10(conf-if-po-1)# lacp fallback enable
OS10(conf-if-po-1)# lacp fallback timeout 20
View LACP fallback conguration
OS10# show port-channel summary
Flags: D - Down I - member up but inactive P - member up and active
U - Up (port-channel) F - Fallback enabled
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Group Port-Channel Type Protocol Member Ports
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1 port-channel1 (UF) Eth DYNAMIC 1/1/10(P) 1/1/11(I)
LACP fallback in non-VLT network
In a non-VLT network, LACP fallback enables rebooting of ToR or server connected to the switch through normal LACP. The other end of
the switch is connected to a DHCP/PXE server, as shown in the following illustration:
Layer 2
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