Owner's Manual

If the VLT port is an internal port in the fabric, FDB entries are not learned on VLT ports, because a flow

traveling through the VLT pair would have multiple paths between the VLT pair switches. The forwarding

entries are programmed in both of the VLT pair switches based on the multiple paths between the

endpoints.

VLT Link Failure

VLT link failures are handled based on the link type and the location of the VLT nodes (inside or outside

the fabric). If a link between the head node and the leaf node fails, the controller performs the following

actions:

1. Opens VLT blocking on the equivalent VLT port.

2. Redirects all flows destined for the impacted VLT port to the VLTi port.

VLT Interconnect (VLTi) Failure

VLTi link failures are handled by the controller based on whether the leaf nodes are part of the fabric or

not. If the leaf nodes are not part of the fabric, the controller identifies one of the VLT pair nodes as the

primary and the other node is assigned a backup role. The controller blocks all VLT ports on the switches

assigned to the backup role. If the link between the VLT pair fails, the controller performs the following

actions:

1. Identifies the primary VLT switch.

2. Administratively disables the VLT ports on the backup switch.

3. Flushes all forwarding entries destined for the blocked VLT ports.

This forces the legacy switch or server that is connected to the fabric to use the remaining link for packet

forwarding. If the leaf nodes are part of the fabric, AFC analyzes the updated topology and reverts to DLF

to manage the switch group. The controller performs the following actions to handle a VLTi failure:

1. Identifies the primary VLT switch.

2. Assigns the primary VLT switch as the root for the DLF tree.

3. Constructs the DLF tree for the DLF traffic.

4. Sets ingress port blocking for ports assigned as alternate ports.

5. Disables VLT blocking in both VLT head nodes.

6. Redirects any forwarding entries destined for the failed link by computing the next shortest path.

Head Node Failure

Head node failures are handled by the controller based on whether the leaf node is part of the fabric or

not. If the head node fails and the leaf nodes are managed by the controller, the controller handles the

failure as a VLTi failure.

Leaf Node Failure

If the leaf nodes are not part of the fabric, the controller disables VLT blocking on the remaining switch.

Because the unavailable leaf node is an external entity, the controller does not make any configuration

changes. The external entity receives the link down notification and the nodes handle the event based on

their methodology. If the leaf node is unavailable, both of the VLT ports in the pair are unavailable as well.

The controller disables VLT blocking on the ports connecting to the leaf node and removes the port

channel created for these ports. The controller flushes the FDB entries configured on these ports.

Supported Technologies and Protocols