Could be worth to note that an RODC can also be a DNS server for
the respective BO. As it is designed for one-way replication from a writeable
DC, it does not allow direct dynamic updates of DNS records that are requested
to be updated by clients that use the RODC as a DNS server (same is true for
password changes) => these are basically forwarded to the next writeable DC
and then replicated back to the RODC. Sounds complicated, but makes sense as the
RODC should be regarded as an “untrusted” DC. I am certainly a friend of combining RODC with Server Core for BO
environments. Combine this with the Admin Separation features of RODC and you
have a great BO story. Admin Separation means that you can make a non-domain
admin a member of the local admin group on an RODC, without granting him/her
admin rights in AD. Server Core will obviously not only be useful for BOs –
they can also host writeable DCs in a company’s datacenters. Biggest challenge I see is configuring the policies for storing
credentials on RODCs – it’s the typical challenge of matching
mobile objects (users and notebooks) to non-mobile devices (an RODC in a site).
And currently this is all based on group memberships. I hope to see an option coming
up to use OU’s instead. I do agree with Al, that the original blog entry that started this
discussion was a little misleading and didn’t do the features of RODC
justice. /Guido From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Eric Fleischman Hi Al, Take your workstation and take a sniff of a logon. All traffic you
throw at the DC will work against the RODC. The only WAN traffic in that
scenario would be the auth itself, a tiny amt of work. (assuming GC and all
that is satisfied locally) So, the statement that authentication is your biggest use is true,
kinda…you need to more carefully define the operation. I suspect you
don’t mean auth in the Kerberos sense, you mean “user logon”
really. Unless your branch has a bunch of apps that do Kerb work and no
clients….then you can correct me and we have a totally different
conversation on our hands. :) Answering some questions of yours, from this and other forks of the
thread….. > What conditions would make it so that the password
policy would be configured such that the password replication > was not allowed? There is a policy (not group policy, administrative one defined in
AD itself) which defines what can be cached there and what can not. The
statement made (I think first by Dmitri, but I then commented on it further)
was that by default, this policy allows almost nothing to be cached. You could
tweak this in your enterprise and change what is cached, anything from the
near-nothing default to almost every secret in the domain. You can choose. > Would that just be that the RODC is no longer trusted
(i.e. it was abducted or otherwise compromised?) Well, we never know if an RODC was compromised. Rather, RODC was
built such that you the admin can assume they are compromised, and fully
understand the scope of compromise in your enterprise should it happen one day,
and respond to said event. So, I say you should look at this problem the other way….
Treat your RODCs as if they were about to get compromised, then make
real decisions around how much work the recovery from said compromise would be
vs. actually having an environment that is useful, reliable, easy to manage,
etc. That’s what I was talking about re: the knobs….you can turn
said knobs and make decisions that work for you. And we’ll have documentation
that will help you do this. > Or is that something that some admin can configure and
hurt themselves? Better yet, if that were true, is there any value left in the > RODC that can't get a password hash? I think I answered this but please holler if it is still unclear. > Outside of "GP work" what else comes to mind
that is off-loaded to the local site that you can think of? Take a network sniff of your clients talking to your DCs for a day.
Almost all of that stuff. J You could have apps, you have logon itself, etc. > Perhaps I'm looking at this sideways? Every environment is different. It is entirely possible that a
secret-less RODC is totally uninteresting in your enterprise. That said, I
would argue that you probably haven’t done enough investigation yet to
really know if that’s true or not…it’s not personal, why
would you? This has likely never been relevant. Almost no one does this sort of
analysis unless they absolutely have to. Take some data, please report back to us. I’d love to look at
said data with you if you’re unclear as to what would fall in what
bucket. Hope this helps. Please holler back with questions. ~Eric From:
[EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Al Mulnick More clarity is always welcome. I suspect I'm trying to get my mind around the GPO providing
that much value that I would want to put a DC in the local brach as part of the
design vs. trying really hard to use as little of the GPO as possible and
making sure that the changes are as infrequent as possible. Authentication and name resolution are my biggest uses for a
local DC in a branch. Outside of Exchange of course. Everything else I
try to keep as compartmentalized as I can because if my WAN is a concern such
that I can't use authentication across the wire (or can't trust it) then I have
some big concerns about the branch environment and how autonomous it is. Outside of "GP work" what else comes to mind that
is off-loaded to the local site that you can think of? Perhaps I'm looking at this sideways? On 7/28/06, Eric Fleischman
<[EMAIL PROTECTED]>
wrote: To
add a bit more… >
The part that makes me wonder about the "story" is if it
stores no secrets is the server doing anything for me? The
short answer is yes. The
bulk of the work that a DC does, even in the auth code path, may not involve
the secret. So even if the secret checking work is "outsourced" to a
hub DC, there is a lot more work that the local DC can perform for the user.
For example, if it is an interactive logon, consider all of the GP work alone
that is done that is now local. At
the end of the day, you have a knob….you can make real security
trade-offs based upon what attack surface you can accept & mitigate, what
administrative story you want, etc. You get to choose what secrets end up on
the RODC. The product is built such that you can turn these knobs as you see
fit but the default knob setting is "more secure". I
hope between my response and Dmitri's you are clear that the belief that it
stores "nothing locally" is incorrect. If more clarity is required
please just holler. ~Eric From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]]
On Behalf Of Dmitri Gavrilov
The
set of passwords that *can* be sent down to the RODC is controlled by
password replication policy. The passwords are sent down by RODC's request, but
the hub also checks whether the user (whose pwd is being requested) actually
attempted to authenticate at RODC (the hub can induce this info from the
traffic is sees). The pwd hash is sent down only if both are satisfied: pwd
policy allows it and the user actually attempted to logon there. Pwd
policy is "empty" by default, i.e. nobody is in "allowed to
reveal" list. It is admin's responsibility to populate this list. We might
have some UI that helps with this process. Once
the hash is sent down, there's no way to remove it from RODC, basically because
we do not trust that RODC will remove it, even if instructed to do so.
Therefore, the only way to "expire" the hash is to change the
password. We store the list of passwords that were sent down to RODC in an
attribute on the RODC computer object (the hub DC updates the list when it
sends a pwd). So, if the RODC is stolen, you can enumerate whose passwords were
down there, and make these users reset their passwords. There's a constructed
attribute that returns only the users whose * current* passwords appear
to be on the RODC. WRT
what data is sent down – currently, we send everything, sans a handful of
"secret" attributes, which are controlled by pwd replication policy.
There's a DCR to be able to configure the list of attributes that can go down
to RODC (aka RODC PAS), but it is not yet clear if we will get it done or not.
Note that the client data access story on RODC becomes quite convoluted
because you don't know if you are seeing the whole object or only a subset of
it. We do not normally issue referrals due to "partial reads". From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]]
On Behalf Of [EMAIL PROTECTED] RODC
stores password hashes only for a pre defined list of users and they are not
stored on a permanent basis. [I'm unclear how the latter is achieved.] The
goal is such that if the RODC were removed from the office then no password
secrets could be extracted from that machine. neil From: [EMAIL PROTECTED]
[mailto:
[EMAIL PROTECTED]] On Behalf Of Al Mulnick The part that makes me wonder about the "story" is if it stores no
secrets is the server doing anything for me? Is there a point to deploying
the server in a remote office other than just being able to point to it in the
closet and say, "see, I do to earn my paycheck!" I'm sure there's more, but I don't yet know which parts are public
information and which are NDA. Can you tell I'm concerned about the story being created? I like stories;
don't get me wrong. But I'm concerned that the story being spun up might
be missing the mark and lead a few people astray. Safe to note that there are some features that differentiate the RODC from a
NT4 BDC and that make it appealing in some cases. But if it actually does not store anything locally, ever, then I'm not sure
it's worth the time to deploy one now is it? Al
On 7/27/06, Susan Bradley, CPA aka Ebitz - SBS Rocks [MVP] < [EMAIL PROTECTED]>
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- [ActiveDir] Read-Only Domai... Susan Bradley, CPA aka Ebitz - SBS Rocks [MVP]
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- RE: [ActiveDir] Read-O... neil.ruston
- RE: [ActiveDir] Re... Dmitri Gavrilov
- RE: [ActiveDir... Eric Fleischman
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