In order to become in Neighbors the routers must know their requirements, for Example in OSPF:
- The interfaces between neighbors should be in the same Area 0 - The interfaces between neighbors should be configured into the same segment of network - The interfaces between neighbors must be configured on the same network type - The interfaces between neighbors must use the same MTU value - They must use the same timers
In EIGRP - The EIGRP process must be configured with the same AS - The interfaces between the routers must be configured with the same segment of network
In RIP - The routing process must configured with the same version
In BGP - The neighbors interface should be configured with the same MTU value - The BGP routers must uses the neighbor command to enable the adjacency - Verify if they are using ebgp-multihop or ttl-security
Now once the routers meet the requirements and everything is ok they can create an adjacency.
Thank you in advance.
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Every routing protocol can create adjacency with their neighbors, in OSPF the word "adjacency" is most used explicitly.
Adjacency can be defined as a relationship between 2 network devices in order to exchange routing information. RIP, EIGRP, IS-IS and BGP protocol can form adjacency as well. In BGP it is also known as BGP peering.