I have Windows Domain level 2008 R2. There are four GC DC in four different physical locations. I have Kerio-based VPN network for replication and remote administration.

Here is how network configured:

     dc1:
     local IP: 192.168.0.10
     VPN IP: 192.168.1.10

     dc2:
     local IP: 10.10.8.11
     VPN IP: 192.168.1.11

     dc3:
     local IP: 10.10.9.12
     VPN IP: 192.168.1.12

     dc4:
     local IP: 10.10.10.13
     VPN IP: 192.168.1.13

That's simple, replication and all works fine but when running dcdiag on dc3 I have an error:

     A warning event occurred.  EventID: 0x000016AF
     During the past 4.12 hours there have been 216 connections to this Domain 
     Controller from client machines whose IP addresses don't map to any of the
     existing sites in the enterprise. 
     <...> 
     The log(s) may contain additional unrelated debugging information. 
     To filter out the needed information, please search for lines which contain text
     'NO_CLIENT_SITE:'. The first word after this string is the client name 
     and the second word is the client IP address.

Here is netlogon.log lines example:

     05/30 12:07:39 DOMAIN.NAME: NO_CLIENT_SITE: dc2 192.168.1.11
     05/31 09:52:11 DOMAIN.NAME: NO_CLIENT_SITE: dc4 192.168.1.13
     05/31 19:49:31 DOMAIN.NAME: NO_CLIENT_SITE: adm-note 192.168.1.101
     07/01 05:16:26 DOMAIN.NAME: NO_CLIENT_SITE: dc1 192.168.1.10

All VPN-joined computers are generates same log line as above. Computer amd-note is for example administrator's notebook, also have VPN.

Question is should I add new AD site and bind VPN subnet 192.168.1.0/24 with that site?