Avoiding "KDC has no support for encryption type while getting initial credentials" by pinning selected KDC

[Osipov, Michael]

> On 08/17/2016 08:51 AM, Osipov, Michael wrote:
> > The keytab contains three keys for one principal: RC4, AES128, AES256.
> > Our home realm is backed up by 80 to 100 KDCs of various Windows Server
> > versions, not all support AES. KDC lookups rely on DNS only and we do
> > not intend to hardcode them in krb5.conf.
> 
> I do not know a lot about administering Active Directory, but I thought
> the usual practice here was to configure the newer AD servers to behave
> as if they were of the least common denominator version.

This would actually lower the security of the entire system. Windows to
Windows avoids hopping by locating the closest working DC and uses it
as long as possible. Such a case should never happen.
 
> > I would expect MIT Kerberos to pin the first working KDC because some
> > Information has been negotiated already but send to a completely
> different
> > KDC. This is annoying because I would expect the communication between
> client
> > and server is predictable.
> 
> The Kerberos authentication protocol is intended to be stateless; if
> different requests during an AS exchange go to different KDCs, that is
> supposed to work.  We have talked about preferring the previously chosen
> KDC during an AS exchange (mostly for the sake of marginal preauth
> mechanism implementations), but I think the code changes necessary to
> implement that properly would be extensive.

Pity :-( What is your general advice. The network is out of my control.

Michael