The Init state indicates that a router can receive Hello packets from its neighbor but it does not see itself in the Neighbor field of the neighbors Hello packets.
The possible causes are as follows:

1. The neighbor is configured with an improper ACL, which filters out the Hello packets sent by the router.
2. The link is faulty. For example, the link is a unidirectional link and can only receive packets rather than send packets. As a result, the Hello packets cannot reach the neighbor. Such a cause is common on an NBMA network.

3. On an NBMA network, mapping is required between Layer 2 and the IP address. In case of static mapping, the key parameter Broadcast is missing.

good to know!

informative

helpful..

good

useful

useful document, thanks