Users Guide

Table Of Contents
1. The ToR/server boots
2. The switch detects the link that is up and checks fallback enabled status. If fallback is enabled, the device waits for the time-
out period for any LACP BPDUs. If there are no LACP BPDUs received within the time period, then the LAG enters into
fallback mode and adds the first operationally UP port to the port channel instead of placing it in an inactive state.
3. Now the ToR/server has one port up and active. The active port sends packets to the DHCP/PXE server.
4. After receiving response from the DHCP server, the ToR/server boots from the TFTP/NFS server.
5. When the ToR/server is fully loaded with the boot image and configurations, the server starts sending LACP PDUs.
6. When the switch receives LACP PDUs from ToR/server, the device comes out of the fallback mode and activates the LAG
through normal LACP process.
LACP fallback in VLT domain
In a VLT domain, LACP fallback enables rebooting of ToR or server that is connected to VLT nodes through VLT port channel.
The other end of the VLT nodes is connected to a DHCP/PXE server, as shown in the following figure:
In the above scenario, LACP fallback works as follows:
1. The ToR/server boots
2. One of the VLT peers takes care of controlling the LACP fallback mode. All events are sent to the controlling VLT peer for
deciding the port that should be brought up and then the decision is passed on to peer device.
3. The controlling VLT peer can decide to bring up one of the ports in either the local port channel or in the peer VLT port
channel.
4. One of the ports, local, or peer, becomes active based on the decision of the controlling VLT peer.
5. Now the ToR/server has one port up and active. The active port sends packets to the DHCP/PXE server.
6. After receiving response from the DHCP server, the ToR/server boots from the TFTP/NFS server.
7. When the ToR/server is fully loaded with the boot image and configurations, the server starts sending LACP PDUs.
8. When the switch receives LACP PDUs from ToR/server, the controlling VLT peer makes the LACP port to come out of the
fallback mode and to resume the normal functionality.
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