Specific DHCP config

aswinthomas · 02-23-2011, 03:52 AM

Hi all,
Im using Ubuntu and due to the nature of my application, I have to configure a DHCP server that assigns addresses that end with bits '10'. The IP addresses must be of the type 10.x.y.z/22

So some examples of IP addr to be assigned:

10.1.2.2
10.12.18.14
10.6.155.6
10.121.76.22
10.5.45.18
...etc

As you see all the IP addr end with '10' binary bits.

How do I write the dhcpd.conf file?

Thanks a lot in advance

Fabio Paolini · 02-23-2011, 09:11 PM

I would say your IP numbers start with 10 instead of ending. Is not it?

If I have got your doubt correctly, here is a peace of code about your dhcpd.conf

Code:

subnet 10.0.0.0 netmask 255.0.0.0 {
range 10.0.0.2 10.253.253.253;
option routers <your IP gateway>;
}

However I am not sure if it realy is what you want.

aswinthomas · 02-23-2011, 11:19 PM

Hi Fabio, thanks for your reply.

It is true that the address must start with 10. But the last two BITS of the whole address must also be '10'. So for the examples that I have provided, the last 2 BITS of the whole address i.e. last 2 bits of 2,14,6,22,18 are also '10'.

10.1.2.2
10.12.18.14
10.6.155.6
10.121.76.22
10.5.45.18

Specifying a range 10.1.2.2 to 10.1.2.2 would solve it partially, but that would make it static. I want the server to pick one address from all the 2^22 addresses in 10.x.y.z/22, when a client joins the network. 22 bits and not 24 bits because the last 2 bits must be predefined as '10'.

Hope its more clear. Really, thanks for the attempt.

Cheers

Fabio Paolini · 02-24-2011, 01:22 AM

Hi aswinthomas, now I think I see your problem. It seems to be a hard one.

I suppose your configuration should be put as

Code:

netmask = 255.0.0.3
subnet  = 10.0.0.2

Writting that in binaries

Code:

netmask = 11111111.00000000.00000000.00000011
subnet  = 00000110.00000000.00000000.00000010

In this way your server will offer IPs that have the first octects equals 00000110 and the last two bits equals '10' and the rest are free to be anything.

But the problem is the range. I do not know how to put a range of IPs in this way. You must put a list with all IPs and of course it would be impossible.