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verifying replication failure with admp and mom 2005

you’ve no doubt seen this error message if you’re monitoring active directory replication.

The following DCs have not updated their MOMLatencyMonitor objects within the specified time period (8 hours). This is probably caused by either replication not occurring, or because the 'AD Replication Monitoring' script is not running on the DC.

Format: DC, Naming Context, Hours since last update

myDCserver, NDNC:DC=DomainDnsZones,DC=myDomain,DC=com, 16

typically, this error is generated when a DC is no longer replicating.  the ADMP script watches changes to an attribute called adminDescription.  under the container MOMLatencyMonitors off the root of the watched naming context, exist objects that represent all of the DCs for that naming context.

for example:

myDCserver, NDNC:DC=ForestDnsZones,DC=myDomain,DC=com, 9

this statement indicates that the domain controller myDCserver has not replicated the required value for 9 hours or more in the naming context of DC=ForestDnsZones,DC=myDomain,DC=com.  there are two places this can fail:

  1. the domain controller is having trouble replicating.
  2. the MOM Agent is not operating correctly to write to the adminDescription.

to narrow down the problem, follow the steps below.

the domain controller may be having trouble replicating.

to validate this condition, we can use repadmin.  issuing the following command gets us some usable data.

repadmin.exe /showrepl myDCserver
    mySite\myDCserver2 via RPC
        DC object GUID: 67x4141y-x526-45xy-x32y-8x04yx041yx7
        Last attempt @ 2008-09-16 09:46:41 was successful. 

it's important to pay attention to the naming context that was specified.  in this case, we see that the last attempt was successful and very close to the current timeframe.  this indicates that replication is not the issue.


the mom agent is not operating correctly to write to the adminDescription.

as stated above, the admp script to check replication uses the objects in these containers to handle a type of synthetic replication.  for the mom agent running the script, it writes to its own object's adminDescription attribute.  in order to see where a problem may exist, we can utilize dsquery to list the current attributes for all objects in the naming context of ForestDnsZones.

dsquery * cn=momlatencymonitors,dc=forestdnszones,dc=cox,dc=com -scope onelevel -attr name admindescription

and receive the following results:

name admindescription
myDCserver 20080916.0301
myDCserver1 20080916.1301
myDCserver2 20080916.1401
myDCserver3 20080916.1501
myDCserver4 20080916.1301
myDCserver5 20080916.1101
myDCserver6 20080916.1301
myDCserver7 20080916.1301
myDCserver8 20080916.1201

from the results, we can determine that this time, the replication alert is actually a mom error as noted by the delta between myDCserver and any other in the list.


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