Inter Site Topology Generators – in shortcut ISTG, is used as repadmin command to generate report of all topology generators in a AD forest.
Unfortunatelly it happens that instead of your DC name, you will see long ID number instead (starting with 0ADEL: …). It can happen when DC was removed improperly (metadata cleanup was not done) or there used to be writeable DC in past and now it’s RODC.
If currently, there is no DC in this site, entry should be removed, if there is DC (but it used to be a different one – for example writeable, and now it’s RODC) – then this entry has to be updated using adsiedit.
Step 1: Run adsiedit.msc and go to Configuration partition -> Sites and find site with broken DC entry.
Step 2: Expand it’s tree and double click on CN=NTDS Site Settings
Step 3: Find and double click on InterSiteTopologyGenerator:
Step 4: This field should be filled with proper DN (not 0ADEL-… entries) of Domain Controller in this site. How to get this DN? Using ADSIEdit -> Configuration Partition -> Sites -> CN=SiteName -> CN=ServerName -> double click on CN=NTDS Settings. Find property called “distinguishedName” and copy it’s value. Now, when you have DC’s DN, just paste it into interSiteTopologyGenerator and apply changes.
Step 5: Run AD replication and then generate repadmin /istg report again to make sure bad entries are gone.