Value,Meaning,Reference
0,Unnumbered interface Adjacency,[RFC8287]
1,Parallel Adjacency,[RFC8287]
2-3,Unassigned,
4,"IPv4, non-parallel Adjacency",[RFC8287]
5,Unassigned,
6,"IPv4, non-parallel Adjacency",[RFC8287]
7-250,Unassigned,
251-254,Reserved for Experimental Use,[RFC8287]
255,Reserved,[RFC8287]