dhcp server issues its own address

Simon Hobson dhcp1 at thehobsons.co.uk
Fri Apr 13 11:33:26 UTC 2007

S Kalyanasundaram wrote:
>Hi all,
>I have got something buggy. I don't know whats wrong.
>I had my configuration file as simply
>ddns-update-style none;
>subnet netmask {
>  range;
>This IP is belong to the machine where the dhcp server is running 
>and i started the "dhcpcd" from another machine. Both are isolated 
>machines and connected together.
>I have got the following logs from the server.
>DHCPREQUEST for from 00:03:47:1f:3d:e2 via eth0: 
>unknown lease
>DHCPREQUEST for from 00:03:47:1f:3d:e2 via eth0: 
>unknown lease
>DHCPDISCOVER from 00:03:47:1f:3d:e2 via eth0
>ICMP Echo reply while lease valid.
>Abandoning IP address pinged before offer
>Reclaiming abandoned lease
>DHCPDISCOVER from 00:03:47:1f:3d:e2 via eth0
>DHCPOFFER on to 00:03:47:1f:3d:e2 via eth0
>DHCPREQUEST for ( from 00:03:47:1f:3d:e2 via eth0
>DHCPACK on to 00:03:47:1f:3d:e2 via eth0
>I am wondering how the dhcp server can issue its own address to the 
>client. It first said abandoning and reclaiming and after that it 
>issued. I am using dhcp v3.0.3. Now the client also shows the IP 
>same as which dhcp server's machine has.
>Is there anything to do with client so that he sends NACK to server 
>to abandon again?

Problem is simple, you configured the server to give out an address 
that wasn't suitable. It abandoned it because first time around the 
'last ditch sanity check' of ping before offer detected that the 
address was in use. Next time around it recovered the address and 
issued it.

The client MAY or MAY NOT detect that the address is in use and 
decline the lease, but the server should not rely on that.

The answer is that this is a PICNIC error - problem in chair, not in 
computer. DON'T tell you server to give out addresses it shouldn't 
give out ! The ISC server does not check for all possible 
misconfigurations, the administrator is expected to know what he is 

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