Kategoriarkiv: DNS

DNS Subnet ordering

In bigger networks today there might be multiple VLAN’s.

Example:

VLAN ID   VLAN Name         IP Subnet
10        Server-VLAN-1     10.10.10.0 /24
11        Clients-VLAN-1    10.10.11.0 /24
12        Clients-VLAN-2    10.10.12.0 /24
13        WIFI-VLAN-1       10.10.13.0 /24

If a Windows Active Directory server is installed in the server VLAN, then by default it will serve the clients within it’s own subnet. Eg. when a client as for the domain itself through nslookup.

In order for getting the DNS server to server all the above subnets, it is needed to modify a registry key.
As we have 4 x class c subnets we can use the table below to find the needed value for the registry key. In this example it will be 0x000003FF.

The easy way to make the change is by opening a CMD as admin and write the command:

Dnscmd /Config /LocalNetPriorityNetMask 0x000003FF

After succesfull change it is needed for the server to reboot.

Dnscmd /Config /LocalNetPriorityNetMask **LocalPriorityNet**

NetMask           Binary                                CIDR    Comments                   LocalPriorityNet

255.255.255.255   11111111.11111111.11111111.11111111    /32      Host (single addr)       0x00000000
255.255.255.254   11111111.11111111.11111111.11111110    /31      Unuseable                0x00000001
255.255.255.252   11111111.11111111.11111111.11111100    /30      2  useable               0x00000003
255.255.255.248   11111111.11111111.11111111.11111000    /29      6  useable               0x00000007
255.255.255.240   11111111.11111111.11111111.11110000    /28     14  useable               0x0000000F
255.255.255.224   11111111.11111111.11111111.11100000    /27     30  useable               0x0000001F
255.255.255.192   11111111.11111111.11111111.11000000    /26     62  useable               0x0000003F
255.255.255.128   11111111.11111111.11111111.10000000    /25     126  useable              0x0000007F
255.255.255.0     11111111.11111111.11111111.00000000    /24     “Class C” 254 useable     0x000000ff

255.255.254.0     11111111.11111111.11111110.00000000    /23       2  Class C’s            0x000001FF
255.255.252.0     11111111.11111111.11111100.00000000    /22       4  Class C’s            0x000003FF 
255.255.248.0     11111111.11111111.11111000.00000000    /21       8  Class C’s            0x000007FF
255.255.240.0     11111111.11111111.11110000.00000000    /20      16  Class C’s            0x00000FFF
255.255.224.0     11111111.11111111.11100000.00000000    /19      32  Class C’s            0x00001FFF
255.255.192.0     11111111.11111111.11000000.00000000    /18      64  Class C’s            0x00003FFF
255.255.128.0     11111111.11111111.10000000.00000000    /17     128  Class C’s            0x00007FFF
255.255.0.0       11111111.11111111.00000000.00000000    /16      “Class B”                0x0000ffff
     
255.254.0.0       11111111.11111110.00000000.00000000    /15      2  Class B’s             0x0001FFFF
255.252.0.0       11111111.11111100.00000000.00000000    /14      4  Class B’s             0x0003FFFF
255.248.0.0       11111111.11111000.00000000.00000000    /13      8  Class B’s             0x0007FFFF
255.240.0.0       11111111.11110000.00000000.00000000    /12     16  Class B’s             0x000FFFFF
255.224.0.0       11111111.11100000.00000000.00000000    /11     32  Class B’s             0x001FFFFF
255.192.0.0       11111111.11000000.00000000.00000000    /10     64  Class B’s             0x003FFFFF
255.128.0.0       11111111.10000000.00000000.00000000    /9      128  Class B’s            0x007FFFFF
255.0.0.0         11111111.00000000.00000000.00000000    /8       “Class A”                0x00ffffff
  
254.0.0.0         11111110.00000000.00000000.00000000    /7                                0x01FFFFFF
252.0.0.0         11111100.00000000.00000000.00000000    /6                                0x03FFFFFF
248.0.0.0         11111000.00000000.00000000.00000000    /5                                0x07FFFFFF
240.0.0.0         11110000.00000000.00000000.00000000    /4                                0x0FFFFFFF
224.0.0.0         11100000.00000000.00000000.00000000    /3                                0x1FFFFFFF
192.0.0.0         11000000.00000000.00000000.00000000    /2                                0x3FFFFFFF
128.0.0.0         10000000.00000000.00000000.00000000    /1                                0x7FFFFFFF
0.0.0.0           00000000.00000000.00000000.00000000    /0    IP subnet definition        0xFFFFFFFF