DHCP client

Pavan Goyal · 07-05-2008, 06:15 AM

Thanks for your response. I also found one more option.
using dhclient eth0 -s 10.10.10.10 will send DHCPDISCOVER request to 10.10.10.10 only.

Pavan Goyal · 07-05-2008, 06:18 AM

I've one more use case....

Between my dhcp client and dhcp server, one cisco relay agent is siting. This relay agent is inserting option 82 in the request coming from dhcp client and sending to server. I need to extract the value from option 82 at dhcp server ....how?
I've ubuntu linux 7.1 on both client and server machine.

Mr. C. · 07-05-2008, 12:34 PM

Ah, nice. My NetBSD system's man page does not show that option, and I've not noticed it before on Linux or other systems. Good find! See... the man pages are our friends! :-)

Mr. C. · 07-05-2008, 12:59 PM

Quote:

Originally Posted by Pavan Goyal

I've one more use case....

Between my dhcp client and dhcp server, one cisco relay agent is siting. This relay agent is inserting option 82 in the request coming from dhcp client and sending to server. I need to extract the value from option 82 at dhcp server ....how?
I've ubuntu linux 7.1 on both client and server machine.

I don't know. Perhaps this:

http://www.thtech.net/article/10

or

man dhcp-options

option extensions-path text;

This option specifies the name of a file containing additional
options to be interpreted according to the DHCP option format as
specified in RFC2132.

http://www.faqs.org/rfcs/rfc2132.html

vesperatus · 10-01-2008, 02:18 PM

This is an old thread but read it following my research on how to use omshell. So i'll post what I found, it might anwser some questions in here.

Quote:

Originally Posted by Pavan Goyal

If there are multiple DHCP servers running, is there is a way to configure client to give preference to a particular server ?

From the dhclient.conf man page you can read that :

Quote:

The select-timeout statement

select-timeout time;

It is possible (some might say desirable) for there to be more than one DHCP server serving any given network. In this case, it is
possible that a client may be sent more than one offer in response to its initial lease discovery message. It may be that one of
these offers is preferable to the other (e.g., one offer may have the address the client previously used, and the other may not).

The select-timeout is the time after the client sends its first lease discovery request at which it stops waiting for offers from
servers, assuming that it has received at least one such offer. If no offers have been received by the time the select-timeout has
expired, the client will accept the first offer that arrives.

By default, the select-timeout is zero seconds - that is, the client will take the first offer it sees.

You can also define new options in the dhcp server, look under DEFINING NEW OPTIONS in the dhcp-options man page. Then, in the dhclient.conf file, you should be able to use the "require" option and query for those new options. I have not tried it yet but it's in the man page.

On my mandriva 2008 system, my dhclient is started with the following command line :

Quote:

dhclient -1 -q -lf /var/lib/dhcp/dhclient-eth0.leases -pf /var/run/dhclient-eth0.pid -cf /etc/dhclient-eth0.conf eth0

.
Funny thing is that the /etc/dhclient-eth0.conf file does not exists and the /etc/dhclient.conf file is also non-existent.... Anyway, still trying to connect with OMSHELL and force a DHCPRELEASE but I need to be able to configure the dhclient first.