The auto-IP feature
is an enhancement of Link Layer Discovery Protocol (LLDP). LLDP uses a set of
attributes to discover neighbor devices. This attribute set is called Type
Length Value (TLV) as it contains type, length, and value descriptions.
In a ring topology,
two network-to-network interfaces (NNIs or node interfaces) of a device are
used to be part of the ring. For a ring to function as an auto-IP ring, you
must configure the auto-IP feature on all the node interfaces within the ring.
One node interface of a device is designated as the owner-interface and the
other interface as the non-owner-interface. In an auto-IP ring, the
owner-interface of a device is connected to a non-owner-interface of the
neighbor device. A sample topology is given below:
![](/content/dam/en/us/td/i/300001-400000/390001-400000/390001-391000/390129.eps/jcr:content/renditions/390129.jpg)
When a new device is
inserted into an auto-IP ring, owner and non-owner-interfaces of the inserted
device are identified. The node interface of the inserted device that is
connected to an owner-interface is designated as the non-owner-interface, and
it automatically receives an IP address from the connected neighbor device. The
IP address is automatically configured on the interface. Since the
non-owner-interface is identified, the other node interface of the inserted
device is designated as the owner-interface, and the device assigns a pre
configured auto-IP address to its designated owner-interface.
An auto-IP address
is a preconfigured address configured on a node interface to make the interface
capable of automatically assigning an IP address to a new neighbor interface
that is detected in the auto-IP ring. The configured auto-IP address is used
for allocation purposes.
You must configure
the same auto-IP address on the two node interfaces that are designated to be
part of an auto-IP ring, and the auto-IP address must contain an odd number in
the last octet. The auto-IP address is assigned to the owner-interface when the
device is introduced into an auto-IP ring. Since each auto-IP address contains
an odd number in the last octet, the IP address derived by subtracting 1 from
the last octet is an even number, and is not used for designating auto-IP
addresses. This IP address is allocated to a newly detected neighbor,
non-owner-interface.
For example, if we
assume that the device R3 is inserted between the devices R1 and R2 in the
above topology, and the auto-IP address 10.1.1.3 is configured on e0/1 and
e0/0, the two node interfaces on device R3, then R1 assigns an IP address to
the non-owner-interface of R3, e0/1. The IP address 10.1.1.3 is assigned to the
owner-interface of R3, e0/0. The IP address derived by subtracting 1 from the
last octet of the auto-IP address is 10.1.1.2. 10.1.1.2 is assigned to the
neighbor non-owner-interface of the connected neighbor device R2.
Auto-IP TLV
exchange
Before insertion,
the node 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.
After a device is
inserted into a ring, the auto-IP address configured for the device (such as
10.1.1.3) 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
node interface (before the node is inserted into a ring), then the ring
interface has priority 1 in the auto-IP TLV.
The IP address
negotiation is based on priority; the higher value of priority wins the
negotiation. If the priority is equal, then IP negotiation fails. This scenario
usually occurs when there is an incorrect configuration or wiring. In such a
scenario, you must ensure that the configuration and wiring is proper.
Auto-IP on VRF
interfaces
Some points on
auto-IP configuration on virtual routing and forwarding instance (VRF)
interfaces are noted below:
- Auto-IP configuration on an
interface is removed when the interface is moved from one VRF to another,
including the global VRF. So, assign the interface to a VRF and then configure
the auto-IP feature on the interface.
- You can configure auto-IP
on a VRF interface only if the address family of the VRF is IPv4. If the IPv4
address family configuration is removed from a VRF, the auto-IP configuration
is removed from all the interfaces within the VRF.
- If a VRF address family is
IPv6, you cannot configure auto-IP on the interfaces within the VRF. However,
if a VRF address family is IPv4 and IPv6, you can configure auto-IP on the
interfaces within the VRF.
- If the IPv6 address family
configuration is removed from a VRF with both IPv4 and IPv6 address-family
configuration, the auto-IP configuration on the interfaces within the VRF
remain intact.
- If a VRF is deleted, then
the auto-IP configuration on all the interfaces assigned to the VRF are
removed.
- A specific ring has two
interface nodes. Ensure that the two nodes you select belong to the same VRF.
Nodes in different VRFs cannot be configured for the same ring.
- Within a VRF, the same
auto-IP address cannot be used for different ring IDs.
Auto-IP on
EtherChannel interfaces
Some points on
auto-IP configuration for an EtherChannel interface are noted below:
- You can configure auto-IP
on an EtherChannel interface. If you configure the auto-IP feature on an
EtherChannel and then add member interfaces to the EtherChannel, then auto-IP
TLV information is carried to all the member interfaces. If you add member
interfaces to the EtherChannel and then configure auto-IP on the EtherChannel,
auto-IP TLV information is carried to all the member interfaces.
![](https://www.cisco.com/content/dam/en/us/td/i/templates/note.gif)
Attention
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LLDP must be enabled on the member interfaces.
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- The list of EtherChannel
member interfaces are maintained in ring interfaces corresponding to the
EtherChannel. Auto-IP information is transmitted on all the EtherChannel member
interfaces.
- If you remove a member
interface from an EtherChannel, auto-IP TLV information is not carried to the
removed interface.
Auto-IP on SVI
interfaces
Some points on
auto-IP configuration on a Switch Virtual Interface (SVI) are noted below:
- Auto-IP configuration on an
SVI is possible only if a single physical interface is associated with an SVI.
- The SVI physical interface
must be an access port or trunk port with only one associated VLAN or a bridge
domain interface (BDI).
- If the SVI is mapped to
more than one physical port, then the auto-IP configuration on the SVI will be
removed.