Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Is this for security reason, or performance reason?

share|improve this question
up vote 5 down vote accepted

Security reason.

With --duplicate-cn, two connections with same common name are allowed, so one cert can be used by more than one connection/users.

Without --duplicate-cn, every vpn cert must have their own CN, so every connection/user have one unique cert.

share|improve this answer

It's actually neither of those reasons. If it had to be one of those two options, you might argue that it's security. However, using duplicate-cn alone does not make your VPN any less secure. There are two reasons that I know. The first is a concern about managing the credentials used to authenticate on the VPN--if many clients use the same certificate, then revoking that certificate also revokes access for all clients that use it, which may or may not be desirable. Also, it is common for a client device to roam and initiate connections from a range of public addresses--in those cases it is more likely desired for that device to retain the same address on the VPN despite the roaming, which requires there to be no more than one connection per client certificate.

A valid use case for duplicate-cn might be where your client devices do not roam and you don't care to control access on a client-by-client basis and your higher priority is not spending too much time managing keys and certificates. I believe the basis of their recommendation is the fact that such cases are in the minority and also that most people don't understand security, much less PKI-based security and they don't want to muddy the waters for such people.

share|improve this answer
This should be the accepted answer. – noumenon Oct 21 '15 at 15:07
The reason we use duplicate-cn is so a user can have the same cert for mobile and laptop. Also unifiy's management of that user. Although I dont know why I get the warning WARNING: using --duplicate-cn and --client-config-dir together is probably not what you want – Christian Jul 8 at 11:42

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.