Open Shortest Path First – OSPF Neighbor States
OSPF (Open Shortest Path First) is a routing protocol used to exchange routing information between network devices in a local area network (LAN) or a wide area network (WAN). In OSPF, devices that are directly connected and exchange routing information are called neighbors. You might want to look at our tutorial on OSPF routing protocol Introduction and Basic OSPF configuration to get started with. But here in this post we shall discuss OSPF neighbor states.
There are several OSPF neighbor states that a device can be in, depending on the status of the OSPF connection between the two devices:
- Down: The OSPF neighbor relationship has not yet been established.
- Attempt: The device is trying to establish an OSPF neighbor relationship, but it has not yet succeeded.
- Init: The device has received a hello packet from its neighbor, but the two devices have not yet exchanged their full routing tables.
- 2-Way: The device has received a hello packet from its neighbor and has exchanged its full routing table with the neighbor. However, the device has not yet received a full routing table from its neighbor.
- Exstart: The device is in the process of exchanging its full routing table with its neighbor and is negotiating the starting point for the exchange.
- Exchange: The device is exchanging its routing table with its neighbor.
- Loading: The device has received a full routing table from its neighbor and is in the process of incorporating the information into its own routing table.
- Full: The device has established a full OSPF neighbor relationship with its neighbor and is exchanging routing information normally.
It’s important to note that OSPF neighbors must be fully adjacent, meaning they must be directly connected to each other and be able to exchange hello packets. If a device is unable to establish an OSPF neighbor relationship with a device, it could be due to a variety of issues, such as a misconfigured OSPF process ID or hello interval, an incorrect network type or area ID, or a connectivity issue between the two devices.