ANR is one of the SON features, used to establish connection between two cells which are neighbor to each other and belong to different eNodeBs. ANR stands for Automatic Neighbor Relationship. Initially, eNodeB configures UEs to get cells information neighbor to that cell. UE sends measurement reports to source cell, carries PCI "Physical Cell Identity" . If cell is not aware about physical cell identity reported by UE then cell may configure UEs to report ECGI, TAC and broad casted PLMNs for a detected neighbor cell.
Once cell receives ECGI of neighbor cell, it resolves ECGI to transport layer address for making X2 setup connection.