Users Guide

Table Of Contents
About GRE Tunnel Groups
The controller supports redundancy of Generic Routing Encapsulation (GRE) tunnels for both Layer-2 and
Layer-3 GRE tunnels. This feature enables automatic redirection of the user traffic to a standby tunnel when
the primary tunnel goes down.
A tunnel group is identified by a name or number. You can add multiple tunnels to a tunnel group.
Tunnel Group Order
The order of the tunnels defined in the tunnel-group configuration specifies their standby precedence. The first
member of the tunnel-group is the primary tunnel.
Tunnel Failover
A GRE tunnel group combines two tunnels created in the controller, where one tunnel is active and the other
tunnel is the standby. Traffic forwarding can occur on the active tunnel, and the standby tunnel can become
active once the active tunnel is down.
When the first tunnel fails, the second tunnel carries the traffic. The third tunnel in the tunnel-group takes over
if the second tunnel also fails.
In the meantime, if the first tunnel comes up, it becomes the most eligible standby tunnel.
Preemption
You can also enable or disable preemption as part of the tunnel-group configuration. Preemption is enabled by
default. (For CLI examples, see Enabling Preemption on page 121.)
The preemptive-failover option automatically redirects the traffic whenever it detects an active tunnel with a
higher precedence in the tunnel group.
When preemption is disabled, the traffic gets redirected to a higher precedence tunnel only when the tunnel
carrying the traffic fails.
Enabling a Tunnel Group
To enable this tunnel-group functionality, you must complete the following tasks:
1. Configure the member tunnel.
2. Enable tunnel keepalives on the tunnel interface.
3. Configure the tunnel group and set the group type to Layer-2 or Layer-3.
4. Add the member tunnels to the group.
Points to Remember
l When a tunnel is added to the tunnel group, the tunnel is used for data traffic only if it is the active tunnel in
the group.
l Standby tunnels do not carry any data traffic. However, all tunnels in the group continue to send and
receive keepalive packets.
l Only one type of tunnel can be placed into a tunnel group—either Layer-2 or Layer-3. That is, you can't have
a tunnel group consisting of both Layer-2 and Layer-3 tunnels.
l The default value of tunnel group type is Layer-3.
Regarding Layer-2 Tunnel Groups
When creating a Layer-2 tunnel group, keep in mind the following:
l All tunnels in a Layer-2 tunnel group must be tunneling the same VLAN.
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