I'm guessing the rid is a random chosen id number for the secondary server (consumer?) that is used to compare the master db (entryuuid?) for context? information that indicates sync state?rid is chosen by administrator (i.e. manually configured). I honestly forget what it's used for nowadays...I vaguely remember "nothing" and/or "it's only important for multimaster." I'm certain this is in the archives of openldap-software and/or openldap-devel, but I'll leave the search to you.
The RID value is a unique number in a given replica used to specifically identify that particular syncrepl statement. It really only matters if you have multiple syncrepl statements in a given slapd configuration for a replica. For me, since I only replicate from a single master, I use the same RID value on all my replicas.
With MMR, there is also the SID, which may be the other part you are thinking of, but if you aren't using MMR, it doesn't apply.
--Quanah -- Quanah Gibson-Mount Principal Software Engineer Zimbra, Inc -------------------- Zimbra :: the leader in open source messaging and collaboration