domain controller error id: 5807

central(main domain controller) London DC1------------------DC2(secondary) Mancester
                                                                       ------------------DC3(secondary) Liverpool

I am a central DC1 admin and i have two more DCs other cities.All are windows 2008 domain controller servers.

I get error

ID:5807
Description:
During the past 4.04 hours there have been 1000 connections to this Domain Controller from client machines whose IP addresses don't map to any of the existing sites in the enterprise. Those clients, therefore, have undefined sites and may connect to any Domain Controller including those that are in far distant locations from the clients. A client's site is determined by the mapping of its subnet to one of the existing sites. To move the above clients to one of the sites, please consider creating subnet object(s) covering the above IP addresses with mapping to one of the existing sites.  The names and IP addresses of the clients in question have been logged on this computer in the following log file '%SystemRoot%\debug\netlogon.log' and, potentially, in the log file '%SystemRoot%\debug\netlogon.bak' created if the former log becomes full. 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. The maximum size of the log(s) is controlled by the following registry DWORD value 'HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters\LogFileMaxSize'; the default is 20000000 bytes.  The current maximum size is 20000000 bytes.  To set a different maximum size, create the above registry value and set the desired maximum size in bytes.

I controlled %SystemRoot%\debug\netlogon.log and there is :

10/21 18:01:55 TREND: NO_CLIENT_SITE: NB016 10.242.2.38

I use C Class IP addreses and wanted one more subnet for my new building computers.for that i did MASK: 255.255.240.0
  current network IP: 192.168.100.0 255.255.255.0
after create new subnet i changed all current IP and Device IPs :
     192.168.100.0 -255.255.240.0
and i created a new subnet under DC1 192.168.96.0/20

but get this error. I do not correct something?

Thanks for your comments