Manually configured tunnels can provide communication between two isolated IPv6 domains over an IPv4 network.
Manually configured tunnels are point-to-point.
Note
The router or host at the source and destination ends of the tunnel must support both IPv4 and IPv6 protocol stacks.
Caution
Ensure that all single-homed point-to-point traffic ingresses and egresses a configured tunnel. Otherwise the traffic is dropped.
IPv6 reachability enables tunnel forwarding but tunnel operational status depends on the IPv4 reachability of the tunnel endpoint.
The IPv4 tunnel endpoint configuration must be symmetrical; that is, if you configure a tunnel with a source of 10.10.10.1 and a destination of 11.11.11.1 from switch A, then Switch B must have a source of 11.11.11.1 and a destination of 10.10.10.1.
Tunnel interfaces are logical point-to-point interfaces.
You can enable dynamic routing when you enable a routing protocol, for example OSPFv3, on the tunnel interfaces.
There is no explicit signaling protocol applied to IPv6-in-IPv4 configured tunnels (refer to RFC 4213).
Therefore, if the remote endpoint of a tunnel that terminates several Layer 3 hops away in the network fails, the local state of the tunnel remains active even though the endpoint has failed.
However, you can enable unicast routing protocols over tunnels, for example OSPFv3. These unicast routing protocols introduce their own protocol-specific signaling and, when a unicast routing protocol is present over the tunnel link, the routing protocol can detect link loss and re-direct the IPv6 route information to use an alternate, reachable nexthop.
The switch must be able to locally detect operational events that can trigger a tunnel state transition.
deletion of local IPv4 interface
change or loss of the IPv4 route to the remote tunnel endpoint
change in the nexthop of the IPv4 route to the remote tunnel endpoint
loss of the ARP entry for the nexthop router that is used to reach the IPv4 tunnel endpoint
You cannot configure the MTU for tunnels.
The default MTU value for tunnels is 1280.
Packets are forwarded through the tunnel using the line card network processing units (NPUs) only. Since the packets are not forwarded through the central processing unit (CPU) they do not impact the CPU load.
You must configure an IPv6 tunnel and static routes on BGP+ peers when you use BGP+. For more information on IPv6 tunnel configuration for BGP+, see IPv6 Tunnel Configurations for BGP+.