Relay agent with dhcp server on same subnet

Glenn Satchell Glenn.Satchell at
Thu Nov 19 11:18:47 UTC 2009

Perhaps you could set up a class to match when there was not an
option-82 present in the request, then to put "ignore booting" inside
that class. Something like

class "ignore_me" {
	match if not exists option agent.circuit-id;
	ignore booting;

That might make dhcpd ignore the direct broadcasts.

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.

>From: "Autuori Gianluigi" <Autuori.Gianluigi.Wintime at>
>To: "Users of ISC DHCP" <dhcp-users at>
>So the only way to do it correctly is to use a switch that suppress the 
original broadcast DHCP packets. The one I use doesn't permit this.
>Gianluigi Autuori
>-----Messaggio originale-----
>Da: dhcp-users-bounces at [mailto:dhcp-users-bounces at] 
Per conto di Bruce Hudson
>Inviato: mercoledì 18 novembre 2009 22.45
>A: dhcp-users at
>Oggetto: Re: R: R: Relay agent with dhcp server on same subnet
>> I think server nakew client request because there isn't any 
>> agent.circuit-id field in its packet.
>    You are correct. Your switch is acting as a DHCP relay but it does not 
appear to be suppressing the original broadcast DHCP packets. This means your 
server is seeing every request twice: once directly from the client without 
relay information and one via the switch that includes the relay option. 
>    The direct DISCOVER would have generated an error message in the server's 
log that no addresses were free and dropped. However, the direct REQUEST 
generates a NAK.
>    This is probably a configuration error in the switch.
>Bruce A. Hudson			| Bruce.Hudson at Dal.CA
>ITS, Networks and Systems		|
>Dalhousie University			|
>Halifax, Nova Scotia, Canada		| (902) 494-3405
>dhcp-users mailing list
>dhcp-users at

More information about the dhcp-users mailing list