FAL[client, ARC0]: Error 12154 for fetching gap sequence

Recently I came across the following error : ERROR: failed to establish dependency between database ps1 and diskgroup resource ora.FRA.dg Error 12154 received logging on to the standby FAL[client, ARC0]: Error 12154 connecting to s1 for fetching gap sequence Error 12154 received logging on to the standby FAL[client, ARC0]: Error 12154 connecting to s2 for fetching gap sequence Lets have a look to see what has happened and resolve. 1) If we log onto the standby and run the following we can see the gap. 1b) Also as a different example you could log onto the ASM standby machine as Oracle and have a look at the archive logs and see if there is any missing. If we look at the list we can identify missing log, it is in sequential order ls78live_1 is thread 1, ls78live_2 is thread 2., We can see below ls78live_1_144812_704059285.arc is missing. 2) On Primary database retrieve the missing archive log files based on the information we got from v$archive_gap. If the archive logs have been already removed you will get the following error. In this case you will need to look through your backed up archive logs. 3) On Standby – lets restore the archive files 12) We now enable the recovery of the standby. Summary We have identified the gap, found the missing archive log's, copied them to the standby and re-enabled the dataguard.