RPCSS kerberos issues on imaged Windows workstations
- by sysadmin1138
While doing some unrelated troubleshooting I came across a set of Event Log entries that have me concerned.
Machine Name: labcomputer82
Source: Security-Kerberos
Event ID: 4
Event Description:
The Kerberos client received a KRB_AP_ERR_MODIFIED error from the server labcomputer143$. The target name used was RPCSS/imagemaster4.ad.domain.edu. This indicates that the target server failed to decrypt the ticket provided by the client. This can occur when the target server principal name (SPN) is registered on an account other than the account the target service is using. Please ensure that the target SPN is registered on, and only registered on, the account used by the server. This error can also happen when the target service is using a different password for the target service account than what the Kerberos Key Distribution Center (KDC) has for the target service account. Please ensure that the service on the server and the KDC are both updated to use the current password. If the server name is not fully qualified, and the target domain (AD.DOMAIN.EDU) is different from the client domain (AD.DOMAIN.EDU), check if there are identically named server accounts in these two domains, or use the fully-qualified name to identify the server.
There are three machine names used in this message. It's generated on labcomputer82, it's attempting to talk to another lab workstation called labcomputer143, and the service in question (RPCSS) refers to the name of the machine that this machine was imaged from (and possibly also that of labcomputer143, I'm not sure). The thing that has me raising both eyebrows is that the machine named labcomputer82 is attempting to use an SPN of RPCSS/imagemaster4.ad.domain.edu.
The SPN attribute on the computer object in AD looks just fine. It has all the names it should have.
Of the over 3,000 computer objects in our AD domain, somewhere around 1,700 of the are computer-lab seats that are frequently imaged. If we're doing something wrong, I'd like to know in time to get our procedures modified (and people retrained) for fall quarter. But if this is normal for imaged machines, I'll just continue ignoring these.
