IP destination address for DHCPOFFER?
dan.sahlin at raycore-fos.com
Wed Jun 27 08:10:00 UTC 2007
I find it quite a bit strange that DHCP clients are supposed to listen to an
IP adress in the DHCPOFFER message that they have not requested or has been
I really had expected that RFC to be more clear that this.
Anyway, the advice I got from Glenn solved my problem.
2007/6/26, Glenn Satchell <Glenn.Satchell at uniq.com.au >:
> You could try this option. It's a grey area, the client is supposed to
> request that responses be broadcast but not all do, so the dhcp server
> gives you the each way option.
> man dhcpd.conf
> The always-broadcast statement
> always-broadcast flag;
> The DHCP and BOOTP protocols both require DHCP and BOOTP
> clients to set the broadcast bit in the flags field of the
> BOOTP message header. Unfortunately, some DHCP and BOOTP
> clients do not do this, and therefore may not receive
> responses from the DHCP server. The DHCP server can be
> made to always broadcast its responses to clients by set-
> ting this flag to 'on' for the relevant scope; relevant
> scopes would be inside a conditional statement, as a
> parameter for a class, or as a parameter for a host
> declaration. To avoid creating excess broadcast traffic
> on your network, we recommend that you restrict the use of
> this option to as few clients as possible. For example,
> >Date: Tue, 26 Jun 2007 14:07:37 +0200
> >From: "Dan Sahlin" <dan.sahlin at raycore-fos.com>
> >What is the proper IP destination address for a DHCPOFFER message?
> >ISC DHCP v3.0.4 uses the new proposed IP address as the destination
> >address in the DHCPOFFER message, i.e. the same as the yiaddr.
> >One DHCP client I have (a managed fiber converter) ignores this
> >DHCPOFFER message as it expects the broadcast IP adress (
> >255.255.255.255) instead.
> >In "The DHCP Handbook" on top of page 107 the DHCPOFFER destination
> >address is shown as the broadcast address. However, the text on the
> >same page says:
> >"This message is sent to the Ethernet broadcast address
> >ff:ff:ff:ff:ff:ff and to the new assigned IP address 192.168.11.25."
> >I do not find the RFC2131 very clear either regarding the proper
> >addressing of DHCPOFFER. In section 3.1.2 it simply says
> >"Each server may respond with a DHCPOFFER message that includes an
> >available network address in the 'yiaddr' field..."
> >So how should the standards properly be interpreted regarding the IP
> >and MAC adresses of the DHCPOFFER message?
> > /Dan Sahlin
> >email: dan.sahlin at raycore-fos.com
> >phone: +46 70 5198187
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