If you see the error %DUAL-6-NBRINFO: EIGRP-IPv4 xxxx is blocked: not on common subnet then it simply means that there are EIGRP devices sending multicast hellos on an interface which have a different IP Range configured to the receiving router. 160617: .Feb 22 15:11:05.194 GMT: %DUAL-6-NBRINFO: EIGRP-IPv4 34256: Neighbor 17 2.31.253.1 (Vlan43) is blocked: not on common subnet (172.31.252.1/31) 160618: .Feb 22 15:11:12.770 GMT: %DUAL-6-NBRINFO: EIGRP-IPv4 34256: Neighbor 19 2.168.205.0 (Vlan44) is blocked: not on common subnet (192.168.204.1/31) ...