The Auto-IP feature is an enhancement of Link Layer Discovery Protocol (LLDP). 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, 2 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.

A ring must have at least one seed device. To configure a device as a seed device in an auto-IP ring, you must manually configure the IP address configured on one of its node interfaces with the auto-IP address of the interface, with the mask '/31' (or 255.255.255.254).

A sample topology is given below. In this scenario, device R1 is being configured as the seed device.

The e0/0 interface on device R1 is configured with the auto-IP address 10.1.1.1 and the e0/1 interface on device R2 is configured with the auto-IP address 10.1.1.3.

To configure R1 as the seed device, the same IP address must be configured as the auto-IP address and the IP address of the interface e0/0. By configuring the IP address of e0/0 interface of R1 to its auto-IP address, R1 becomes the seed device and the interface e0/0 becomes the owner of the subnet.

The process of configuring the device R1 as the seed device is given below:

After a connection is established between the devices R1 and R2, R1 sends a Link Layer Discovery Protocol(LLDP) packet which contains an auto-IP Type Length Value (TLV) with priority 2.

On receiving the auto-IP TLV from R1, R2 derives the IP address for the interface e0/1 (by subtracting 1 from the last octet of R1's auto-IP address), and assigns the IP address 10.1.1.0/31 to R2's e0/1 interface. The interface e0/1 on R2 becomes the non-owner interface on this subnet.

The IP address allocation is displayed in the illustration given below:

The device and node interface details for the subnet are given below:

Note	Since the auto-IP address configured on the e0/1 interface on R2 is 10.1.1.3, the other node interface of R2 is designated as the owner interface and 10.1.1.3 is automatically configured as the interface IP address of the other node interface.

To insert a device into an existing auto-IP ring, the node interfaces of the device must be configured with the auto-IP address.

Note	You can also enable the auto-IP functionality on node interfaces that are part of an existing, but non-auto-IP ring.

The topology in the illustration below explains the sample scenario.

In the topology above, device R1 is configured as the seed device. Interface e0/0 on R1 is configured with the IP address 10.1.1.1/31, and is the owner of the subnet connecting R1 and R2. Interface e0/1 on device R2 has the IP address 10.1.1.0/31, and is the non-owner interface of the subnet.

Device R3 is inserted between R1 and R2. The 2 designated node interfaces e0/0 and e0/1 of R3 are configured with the auto-IP address 10.1.1.5. After the insertion, the ring topology looks like this:

The IP addresses that are configured for the owner and non-owner interfaces on the devices R1, R2, and R3 are given below:

You can remove a device from an existing auto-IP ring.

Note	No configuration is required to remove a device from an auto-IP ring.

The topology in the illustration below explains the sample scenario:

In the topology, device R3 is removed from the auto-IP ring and device R1 is connected to R2. As a result, auto-IP Type Length Value (TLVs) are exchanged between R1 and R2. Since the e0/0 interface of R1 sends an auto-IP TLV with priority 2 and the e0/1 interface of R2 sends an auto-IP TLV with priority 0 to the e0/0 interface on R1, the e0/0 interface of R1 is designated as the owner interface on the subnet connecting R1 and R2. R1 assigns the IP address to the e0/1 interface on R2, and it becomes the non-owner interface on this subnet.

After the removal of R3 from the auto-IP ring, the ring topology looks like this:

The IP address of the owner and non-owner interfaces on the subnet are given below:

If you remove a device from an auto-IP ring, the owner and non-owner auto-IP configuration on the node interfaces is retained. You can insert the device back into an auto-IP ring.

If you incorrectly insert a device into a ring with its interfaces swapped (due to which 2 owner interfaces and 2 non-owner interfaces are connected to each other, rather than a connection between an owner and a non-owner interface), then identical priority values are exchanged between interfaces during the auto-IP Type Length Value (TLV) transmission. Since there is a tie in the priority value that is exchanged between the node interfaces of the inserted device, a conflict is detected.

The 'auto-swap' technique resolves conflicts on both the node interfaces of the inserted device and allows allocation of IP addresses for the interfaces.

Note	No configuration is required to enable the auto-swap technique; it is enabled automatically. Use the auto-swap technique only when conflict is detected on both the node interfaces of the device.

The topology in the illustration below explains the sample scenario:

In this topology, device R3 is incorrectly inserted between the devices R1 and R2, with its interfaces swapped. The conflict arises due to incorrect insertion, as given below:

The auto-IP TLV exchange details between R1 and R3 are given below:

Since the same priority value of 2 is sent in both instances, there is a tie during the election process, leading to a conflict.

Similarly, the same priority value of 0 is exchanged between the e0/0 interface of R3 and the e0/1 interface of R2 since they are non-owner interfaces, leading to a conflict.

Auto Swap

The auto-IP feature uses the auto-swap technique to resolve conflicts on both the node interfaces of the inserted device.

The priority and the interface IP address of the e0/1 interface on R3 is swapped with the priority and the interface IP address of the e0/0 interface on R3, respectively.

After swapping, the following auto-IP TLV information is exchanged between R1 and R3:

• The e0/0 interface on R1 sends an auto-IP TLV with priority 2 to the e0/1 interface on R3.
• The e0/1 interface on R3 sends an auto-IP TLV with priority 0 to the e0/0 interface on R1.

Since the priority sent by R1 to R3 is higher than the priority sent by the interface e0/1 on R3, R3 derives the IP address 10.1.1.0 for the e0/1 interface from the auto-IP address of R1 (10.1.1.1).

The following auto-IP TLV information is exchanged between R3 and R2:

• The e0/0 interface on R3 sends an auto-IP TLV with priority 2 to the e0/1 interface on R2.
• The e0/1 interface on R2 sends an auto-IP TLV with priority 0 to the e0/1 interface on R3.

R2 detects the priority sent by R3 to be higher than the priority sent by its interface e0/1 and derives the IP address 10.1.1.4 from the auto-IP address of R3 (10.1.1.5).

After conflict resolution, the topology looks like this:

The e0/1 interface on R3 is designated as a non-owner interface and the e0/0 interface on R3 is designated as the owner interface.

1.    enable


2.    configure terminal


3.    lldp run


4.    interface type number


5.    auto-ip-ring ring-id ipv4-address auto-ip-address


6.    exit


7.    interface type number


8.    auto-ip-ring ring-id ipv4-address auto-ip-address


9.    ip address interface-ip-address subnet-mask


10.    end


11.    show auto-ip-ring [ring-id][detail]

Device> enable

Device# configure terminal

Device(config)# lldp run

Device(config)# interface ethernet 0/0 

Device(config-if)# auto-ip-ring 4 ipv4-address 10.1.1.1

Device(config-if)# exit

Device(config)# interface ethernet 0/1 

Device(config-if)# auto-ip-ring 4 ipv4-address 10.1.1.1

Device(config-if)# ip address 10.1.1.1 255.255.255.254

Device(config-if)# end

Device# show auto-ip-ring 4 detail

1.    enable


2.    configure terminal


3.    lldp run


4.    interface type number


5.    auto-ip-ring ring-id ipv4-address auto-ip-address


6.    exit


7.    interface type number


8.    auto-ip-ring ring-id ipv4-address auto-ip-address


9.    end


10.    show auto-ip-ring [ring-id][detail]

Device> enable

Device# configure terminal

Device(config)# lldp run

Device(config)# interface ethernet 0/1 

Device(config-if)# auto-ip-ring 4 ipv4-address 10.1.1.3

Device(config-if)# exit

Device(config)# interface ethernet 1/1 

Device(config-if)# auto-ip-ring 4 ipv4-address 10.1.1.3

Device(config-if)# end

Device# show auto-ip-ring 4 detail

Perform this task to verify auto-IP functions.

Note	The commands are not in any specific order.

1.    enable


2.    show auto-ip-ring [ring-id][detail]


3.    debug auto-ip-ring {ring-id {errors | events} |errors | events}

Device> enable
          

Device# show auto-ip-ring

Auto-IP ring 1
Auto-IP Address         : 10.1.1.5

Ring Port0              : Ethernet0/0
My Current-IP           : 0.0.0.0
My Priority             : 1

Auto-IP ring 3
Auto-IP Address         : 10.1.1.3

Ring Port0              : Ethernet0/1
My Current-IP           : 0.0.0.0
My Priority             : 1

      

Device# debug auto-ip-ring 1 errors

Auto IP Ring errors debugging is on for the ring id : 1
*Jul 26 11:30:40.541: (Ethernet0/0) priority (value:1) conflict detected,  need admin intervention