Overview#VendorVersion is defined in RCF 3045.
"All LDAP server implementers SHOULD maintain a VendorVersion. Note that this value is typically a release value--comprised of a string and/or a string of numbers--used by the developer of the LDAP server product (as opposed to the supportedLDAPVersion, which specifies the version of the LDAP protocol supported by this server).
This is single-valued so that it will only have one version value. This string MUST be unique between two versions, but there are no other syntactic restrictions on the value or the way it is formatted.
( 220.127.116.11.1.5 NAME 'vendorVersion' EQUALITY 18.104.22.168.4.1.1422.214.171.124 SYNTAX 126.96.36.199.4.1.14188.8.131.52.15 SINGLE-VALUE NO-USER-MODIFICATION USAGE dSAOperation )
The intent behind the equality match on VendorVersion is to not allow a less than or greater than type of query. Say release "LDAPv3 8.0" has a problem that is fixed in the next release "LDAPv3 8.5", but in the mean time there is also an update release say version "LDAPv3 8.01" that fixes the problem. This will hopefully stop the client from saying it will not work with a version less than "LDAPv3 8.5" when it would also work with "LDAPv3 8.01". With the equality match the client would have to exactly match what it is looking for.
We have some methods that might help you Determine LDAP Server Vendor.