Basic concepts

IRF uses two member roles: master and standby (called subordinate throughout the documentation).

When devices form an IRF fabric, they elect a master to manage and control the IRF fabric, and all the other devices back up the master. When the master device fails, the other devices automatically elect a new master. For more information about master election, see "Master election."

An IRF fabric uses member IDs to uniquely identify and manage its members. This member ID information is included as the first part of interface numbers and file paths to uniquely identify interfaces and files in an IRF fabric. For more information about interface and file path naming, see "Interface naming conventions" and "File system naming conventions."

If two devices have the same IRF member ID, they cannot form an IRF fabric. If the IRF member ID of a device has been used in an IRF fabric, the device cannot join the fabric.

An IRF port is a logical interface that connects IRF member devices. Every IRF-capable device supports two IRF ports. The IRF ports are named IRF-port n/1 and IRF-port n/2, where n is the member ID of the device. The two IRF ports are referred to as IRF-port 1 and IRF-port 2 in this book.

To use an IRF port, you must bind a minimum of one physical interface to it. The physical interfaces assigned to an IRF port automatically form an aggregate IRF link. An IRF port goes down only if all its IRF physical interfaces are down.

IRF physical interfaces connect IRF member devices and must be bound to an IRF port. They forward the IRF protocol packets between IRF member devices and the data packets that must travel across IRF member devices.

For more information about physical interfaces that can be used for IRF links, see "IRF physical interface requirements."

An IRF link failure causes an IRF fabric to split in two IRF fabrics operating with the same Layer 3 settings, including the same IP address. To avoid IP address collision and network problems, IRF uses multi-active detection (MAD) mechanisms to detect the presence of multiple identical IRF fabrics, handle collisions, and recover from faults.

One IRF fabric forms one IRF domain. IRF uses IRF domain IDs to uniquely identify IRF fabrics and prevent IRF fabrics from interfering with one another.

As shown in Figure 2, IRF fabric 1 contains Device A and Device B, and IRF fabric 2 contains Device C and Device D. Both fabrics use the LACP aggregate links between them for MAD. When a member device receives an extended LACPDU for MAD, it checks the domain ID to see whether the packet is from the local IRF fabric. Then, the device can handle the packet correctly.

IRF split occurs when an IRF fabric breaks up into multiple IRF fabrics because of IRF link failures, as shown in Figure 3. The split IRF fabrics operate with the same IP address. IRF split causes routing and forwarding problems on the network. To quickly detect a multi-active collision, configure a minimum of one MAD mechanism (see "Configuring MAD").

IRF merge occurs when two split IRF fabrics reunite or when two independent IRF fabrics are united, as shown in Figure 4.

Member priority determines the possibility of a member device to be elected the master. A member with higher priority is more likely to be elected the master.