Split Horizon

Split horizon enables the creation of groups of tunnels, which do not bridge between each other. This facilitates loop free mesh topologies without requiring a loop prevention protocol such as Spanning Tree.

Split Horizon is supported on L2 GRE and VXLAN tunnels. L2 GRE and VXLAN tunnels have a virtual bridge port bound to them called a tunnel bridge port. This tunnel bridge port is added to VLAN egress lists like any other bridge port in the system. The Split Horizon feature is configured by assigning a Split Horizon group to the L2 GRE or VXLAN tunnel The Split Horizon feature comes into play when the switch bridges a packet from one tunnel bridge port to another in the same VLAN. If the tunnels bound to these tunnel bridge ports are in the same Split Horizon group, the switch does not forward the packet on the tunnel belonging to the Split Horizon group.

Split Horizon groups are identified by a number in the range of 1 to the maximum tunnel ID value supported on the platform. The S-Series supports a range of 1 - 62. The K-Series supports a range of 1 - 16.

Bridging between tunnels assigned to different Split Horizon groups behaves as though Split Horizon is not configured. Only when tunnels are placed into the same Split Horizon group is bridging between them disabled. All of the tunnels in a given platform may be placed into the same group.

Routing between tunnels occurs normally without any reference to Split Horizon groups.

Use the tunnel split-horizon-group command in tunnel configuration mode to assign the tunnel to a split-horizon-group.