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The Machine SID Duplication Myth
toppings writes "Microsoft Technical fellow Mark Russinovich explains why he is now retiring NewSID, which has been used by IT departments for years when deploying Windows to new systems from customized clone images. Russinovich writes: 'The reason that I began considering NewSID for retirement is that, although people generally reported success with it on Windows Vista, I hadn't fully tested it myself and I got occasional reports that some Windows component would fail after NewSID was used. When I set out to look into the reports I took a step back to understand how duplicate SIDs could cause problems, a belief that I had taken on faith like everyone else. The more I thought about it, the more I became convinced that machine SID duplication — having multiple computers with the same machine SID — doesn't pose any problem, security or otherwise. I took my conclusion to the Windows security and deployment teams and no one could come up with a scenario where two systems with the same machine SID, whether in a Workgroup or a Domain, would cause an issue. At that point the decision to retire NewSID became obvious.' He concludes: 'It's a little surprising that the SID duplication issue has gone unquestioned for so long, but everyone has assumed that someone else knew exactly why it was a problem. To my chagrin, NewSID has never really done anything useful and there's no reason to miss it now that it's retired. Microsoft's official policy on SID duplication will also now change and look for Sysprep to be updated in the future to skip SID generation.'"
"As I said earlier, there’s one exception to rule, and that’s DCs themselves. Every Domain has a unique Domain SID that’s randomly generated by Domain setup, and all machine SIDs for the Domain’s DCs match the Domain SID. So in some sense, that’s a case where machine SIDs do get referenced by other computers. That means that Domain member computers cannot have the same machine SID as that of the DCs and therefore Domain. However, like member computers, each DC also has a computer account in the Domain, and that’s the identity they have when they authenticate to remote systems. All accounts in a Domain, including computers, users and security groups, have SIDs that are based on the Domain SID in the same way local account SIDs are based on the machine SID, but the two are unrelated."
The low ramifications of this as mentioned above may have changed post Win2K and XP. This particular caveat governed our processes as system deployment specialists for Microsoft corporate events. We had to make sure that any potential DC had a unique SID even before the machines were promoted to DC, otherwise we saw (verifiably!) many issues with Workstations failing to join the domain. I seem to recall other more esoteric issues with older Microsoft server products, but that may be delusions based on the mass hysteria we had about unique SIDs at the time.
Did you mean the SusClientId? AFAIK this is the only identifier WSUS uses to distinguish between computers (they also don't have to be on the same domain).
On new clones you only need to delete the SusClientId key under HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate; the update service will take care of assigning the machine a new ID.
It's not for domain controllers in general it's for the very first domain controller used to initialize a brand new domain. You want to never create a new server with that same SID again. The first domain controller's SID is special, it will be used to generate the domain SID. From then on, all subsequent domain controllers promoted in the domain will have the same machine SID.
So you're good if you create the very first DC with a unique install, and clone all your other servers from an image.
As I said earlier, there’s one exception to rule, and that’s DCs themselves. Every Domain has a unique Domain SID that’s randomly generated by Domain setup, and all machine SIDs for the Domain’s DCs match the Domain SID. So in some sense, that’s a case where machine SIDs do get referenced by other computers. That means that Domain member computers cannot have the same machine SID as that of the DCs and therefore Domain. However, like member computers, each DC also has a computer account in the Domain, and that’s the identity they have when they authenticate to remote systems. All accounts in a Domain, including computers, users and security groups, have SIDs that are based on the Domain SID in the same way local account SIDs are based on the machine SID, but the two are unrelated.
issue is if a distributed application used machine SIDs to uniquely identify computers. No Microsoft software does so and using the machine SID in that way doesn’t work just for the fact that all DC’s have the same machine SID.
This is absolutely correct.
Identical machine SIDs and WSUS identifiers (stored in the registry) don't stop the updates from being applied...they just cause the WSUS reports to show only the details for the last cloned machine that connected.
I ran into this same issue. I've now got a batch script that runs at first logon (post-reimaging) that resets the client ID. Probably overkill at this point (the bad image that was causing this has long since been redone), but it ensure that every machine checks in with a fresh key.
net stop wuauserv /v SusClientId /f /resetauthorization /detectnow
reg delete "HKEY_LOCALMACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Windowsupdate"
net start wuauserv
wuauclt.exe
That does require a more windows update client (the old wuauclt only accepted a couple of options, including detectnow, and ignored the reset. If you typed wuauclt.exe /gogetmeabeerandasteak it wouldn't throw an error, it just looked like it ran).
There's a distinct difference between the SID and the SusClientID.
There are some people that if they don't know, you can't tell 'em.