If 2 DCs independently add a single-valued linked attribute to an object, but link it to 2 different target objects, then replication cannot resolve this inconsistency. The replications stops due to this error and the 2 DCs won't be able to replicate to each other after this. Currently it fails with the following error: ../source4/dsdb/repl/replicated_objects.c:938 Failed to prepare commit of transaction: prepare_commit error in module repl_meta_data: Attribute or value exists (20) Failed to commit objects: WERR_GEN_FAILURE/NT_STATUS_INVALID_NETWORK_RESPONSE A test has been added to demonstrate this problem (currently it's a known-fail). https://git.samba.org/?p=samba.git;a=commit;h=1541c50b370e8695bf5c958cc41073d1552a3c52
Fixed in Samba 4.8. See main commits: https://git.samba.org/?p=samba.git;a=commit;h=f196897bc822f7133627477e77a4bcd98b8ceda6 https://git.samba.org/?p=samba.git;a=commit;h=82b56e63b5cb7e19a580a7cdeaf1caa8608852bc (plus several other refactor commits marked with bug #13055)