how to configure DHCP relay with ISC.

Guo, Fei Fei.Guo at
Tue Apr 27 09:50:45 UTC 2010

Hi Glenn and All

  first of all, thank you very much. But I setup the environment with the configuration that you listed, DHCP server discard the DISCOVERY packet, I do not know why, can you give me some advice. And how to debug the server??? Thank you very much.
  The attachment is the capture packet from the server side. And the following is my configuration on the DHCP server.
# dhcpd.conf
# Sample configuration file for ISC dhcpd

# option definitions common to all supported networks...
option domain-name "";
option domain-name-servers;

# This is a very basic subnet declaration.
subnet netmask {

subnet netmask {
  option routers;

-----Original Message-----
From: at [ at] On Behalf Of Glenn Satchell
Sent: 2010年4月15日 19:59
To: Users of ISC DHCP
Subject: Re: how to configure DHCP relay with ISC.

On 04/15/10 17:11, Guo, Fei wrote:
> Hello All,
> can you give me an example about how to configure on the 
> client/relay/server side, I have installed 4.1.1 version, a simple 
> topology is the following:
> client ------------------------------------------ relay
> ------------------------------------------ server
> eth1 I want get a IP address on 
> client "eth1", it should be in net "192.168.1.x/24". thank you very 
> much.
> Cheers
> Fei
> _______________________________________________
> dhcp-users mailing list
> dhcp-users at

A fairly minimal example would be something like this.

client ---------------------- relay ---------------------- server

Relay configuration

The only important item to note is that you must listen on interfaces where you expect to recieve dhcp requests *and* listen for packets from the dhcp server. The default is to listen on all interfaces.

$ man dhcrelay

Server Configuration

Configure local and remote subnets identically. The server automatically switches the incoming requests to the right subnet. The server must have a configuration for the local subnet, even if it is not used for any dhcp services.

$ man dhcpd.conf
# global settings for all subnets
option domain-name "";
option domain-name-servers;
subnet netmask { } subnet netmask {
	# settings just for this subnet
	option routers;

Other man pages worth reading are dhcpd, dhcp-options, dhcp-eval. In total there would be close to 100 pages of documentation in the man pages. Of course, if there are any other questions please feel free to post them here,,,


Glenn Satchell                            |  Miss 9: What do you
Uniq Advances Pty Ltd, Sydney Australia   |  do at work Dad?
mailto:glenn.satchell at         |  Miss 6: He just tel:0409-458-580   |  types random stuff.
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