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Error Message %DUAL-6-NBRINFO: EIGRP-IPv4 34256


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 172.31.253.1 (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 192.168.205.0 (Vlan44) is blocked: not on common subnet (192.168.204.1/31)                                                                                        
This is most likely to occur by accident when two subnets are configured on the same VLAN, with EIGRP running on the interface.

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