I'm trying to break my network into different subnets.

Server is located into subnet.

I have the following declaration in my dhcp.conf:

subnet netmask {

option routers; 


When I'm trying to change it to another range:

subnet netmask {

option routers; 


No addresses are allocated. Even if I'm trying to create fixed address:

host mee-laptop {

   hardware ethernet 10:(..);


Server won't assign this address to my computer.

I tried to created virtual interface in subnet, but it didn't help.

Also, when I'm setting my computer address manually it works and I'm able to access network as well as network, but when I'm creating server virtual interface with address in 14.0/24 network again I'm not able to reach server and other networks from my computer.


My /etc/networking/interfaces file:

auto lo
iface lo inet loopback

auto eth0
        iface eth0 inet static

auth eth0.2
iface eth0.2 inet static
        vlan-raw-device eth0

Here is a part of dhcpd.log with information about my interface:

Feb 13 14:26:52 mario dhcpd: uid lease for client 7c:c3:a1:a7:54:c3 is duplicate on
Feb 13 14:26:52 mario dhcpd: DHCPREQUEST for from 7c:c3:a1:a7:54:c3 via eth0
Feb 13 14:26:52 mario dhcpd: DHCPACK on to 7c:c3:a1:a7:54:c3 via eth0

And here is what's going on in tcpdump:

14:29:21.498248 IP > BOOTP/DHCP, Request from 7c:c3:a1:a7:54:c3, length 300
14:29:21.498469 IP > BOOTP/DHCP, Reply, length 300
  • Can you clarify if your 14 and 15 networks are on the same physical network without any router between them ? – Bertrand SCHITS Feb 13 '14 at 10:29
  • @BertrandSCHITS same physical network, but there is a media converter and router between my computer and server. – Mee Feb 13 '14 at 10:30

I am not fully sure what you are trying to achieve. I can see two possibilities:

  1. You have TWO subnets with router in between and want to have ONE DHCP server responsible for IP address assignement. In this case you likely should have a look at dhcprelay (which is also a part of isc-dhcp) or so called "ip helper" or "dhcp helper" on a switch / router.
  2. You want two SHARE single physical network segment between TWO subnets. In this case you have to put both subnets in shared-network statement.
| improve this answer | |

This should be a comment asking for more information but i don't have enough rep to do that :-/

You should add details of your network interfaces on the server (ifconfig output) and possibly add the output of /var/log/dhcpd.log (or whatever configuration file you use). You can get information on how to do that on http://prefetch.net/articles/iscdhcpd.html

Dhcpd doesn't give addresses if it hasn't an interface binded to that subnet. It gives an error like

No subnet declaration for eth0 (no IPv4 addresses).
dhcpd: ** Ignoring requests on eth0.  If this is not what
dhcpd:    you want, please write a subnet declaration
dhcpd:    in your dhcpd.conf file for the network segment
dhcpd:    to which interface eth0 is attached. **

Tcpdump of dhcp negotiation will be useful as well to debug the problem.

| improve this answer | |
  • thanks! I've updated my post with details. Maybe I should remove my host from subnet pool then? – Mee Feb 13 '14 at 12:30
  • 1
    Double check if you really want netmask in eth0 configuration. I think it collides with the alias on – Andrea Feb 13 '14 at 12:58
  • thanks, unfortunately that didn't help. What's strange now, that DHCP assigns me address reserved for another mac address. – Mee Feb 13 '14 at 14:06

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