[Samba] occasional interSiteTopologyGenerator differences between DCs

[mj]

Hi,

I am doing regular automated runs of samba-tool ldapcmp, to make sure 
that all our DC's serve the same data. They run samba 4.13.14 on buster.

Since a couple of weeks, we are getting intermittant failures on the 
interSiteTopologyGenerator. These differences appear and also disappear 
'automatically' again. They usually stay for a couple of hours, 
sometimes less.

They look like this:

> * Comparing [DOMAIN] context...
> 
> * Objects to be compared: 2002
> 
> * Result for [DOMAIN]: SUCCESS
> 
> * Comparing [CONFIGURATION] context...
> 
> * Objects to be compared: 1737
> 
> Comparing:
> 'CN=NTDS SITE SETTINGS,CN=DEFAULT-FIRST-SITE-NAME,CN=SITES,CN=CONFIGURATION,DC=SAMBA,DC=COMPANY,DC=COM' [ldap://sambadc4.samba.domain.com]
> 'CN=NTDS SITE SETTINGS,CN=DEFAULT-FIRST-SITE-NAME,CN=SITES,CN=CONFIGURATION,DC=SAMBA,DC=COMPANY,DC=COM' [ldap://sambadc3.samba.domain.com]
>     Difference in attribute values:
>         interSiteTopologyGenerator => 
> [b'CN=NTDS Settings,CN=WINDC2,CN=Servers,CN=Default-First-Site-Name,CN=Sites,CN=Configuration,DC=samba,DC=company,DC=com']
> [b'CN=NTDS Settings,CN=SAMBADC3,CN=Servers,CN=Default-First-Site-Name,CN=Sites,CN=Configuration,DC=samba,DC=company,DC=com']
> 
>     FAILED
> 
> * Result for [CONFIGURATION]: FAILURE
> 
> SUMMARY
> ---------
> 
> Attributes with different values:
> 
>     interSiteTopologyGenerator
> 
> * Comparing [SCHEMA] context...
> 
> * Objects to be compared: 1739
> 
> * Result for [SCHEMA]: SUCCESS
> 
> * Comparing [DNSDOMAIN] context...
> 
> * Objects to be compared: 305
> 
> * Result for [DNSDOMAIN]: SUCCESS
> 
> * Comparing [DNSFOREST] context...
> 
> * Objects to be compared: 21
> 
> * Result for [DNSFOREST]: SUCCESS
> 

I'm not too woried, since everything works, and the situation always 
proves to be only temporarily. We would not even have noticed this 
occasional discrepancy, if we were not running the regular ldapcmp 
though cron.

But can anyone explain why this is happening, and perhaps how we could 
prevent this?

Best,
MJ