newbie - dhcpd

Simon Hobson dhcp1 at
Thu Jan 24 10:23:50 UTC 2008

BuySell wrote:

>Yes, I typed eth0:1 .. and this is virtual ethernet .. my dhcp server still
>not give ip address to my users, did I miss something? ..

Yes, you have a a "shared network" - ie there are two IP subnets 
sharing the same network cable. You MUST tell the server about this 
or it will not work.

Due to fundamental issues - namely that a broadcast packet isn't 
associated with any specific subnet, the server must take it's 
information from teh interface it received the packet on (in this 
case eth0). You CANNOT receive the broadcast on eth0:0 because there 
is no mechanism for differentiating whether a packet sent from to is for eth0 or for eth0:0 !

Thus, the server needs to be told that when it receives the broadcast 
packet from a client on that interface, the client may belong in 
either of two subnets. You do this with the shared network construct :

shared network "somename" {

   subnet ... {

   subnet ... {


Note that the server cannot magically 'know' which subnet the client 
belongs in. In your case you will only give addresses in one subnet 
so there is no problem, in the more general case you need to define 
what client belongs where.

BTW - can you confirm that there isn't another DHCP server attempting 
to serve the subnet ?

More information about the dhcp-users mailing list