For the auto-IP feature to work, Link Layer Discovery Protocol (LLDP) has to be enabled. LLDP supports a set of attributes that it uses to discover neighbor devices. These attributes contain type, length, and value descriptions, and are referred to as a Type Length Value (TLV).
In a ring topology, two network-to-network interfaces (NNIs or node interfaces) of a device are used to be part of a ring. The auto-IP feature is an automatic method to provide IP addresses to the node interfaces inserted into a ring. One node interface is designated as the ‘owner’ interface and the other as the ‘non-owner’ interface.
For a ring to function as an auto-IP ring, you must enable the auto-IP functionality on all the node interfaces within a ring.
Note The 2 node interfaces which are designated to be part of a ring must be configured with the same auto-IP address.
Before insertion, the interfaces are not designated as ‘owner’ and ‘non-owner’. After insertion, the auto-IP TLV is exchanged between the neighbor devices. During this initial negotiation with the adjacent device interfaces, ‘owner’ and ‘non-owner’ interfaces are determined automatically.
Note Auto-IP address is used for allocation purposes only and not used as an IP address for a node interface until the IP address is configured on an interface.
After a device is inserted into a ring, the auto-IP address configured for the device (such as 10.1.1.1) is assigned to the owner interface for the '/31' subnet. An owner interface has a priority 2 in the auto-IP TLV, and a non-owner interface has priority 0 in the auto-IP TLV. If there is no assigned IP address on the ring interface (before the node is inserted into a ring), then the ring interface has priority 1 in the auto-IP TLV.
The IP negotiation is based on priority; the higher value of priority wins the negotiation. If the priority is equal, then IP negotiation fails. This typically means incorrect configuration or wiring. In such a scenario, you must make sure the configuration and wiring is proper.
For more information about auto-IP feature, see Information About Auto-IP.
For more configuration steps, see How to Configure Auto-IP.
For information on CLI commands, see Cisco IOS IP Addressing Services Command Reference and Cisco IOS Master Command List, All Releases.