Is it possible to use Ifconfig to switch an interface to DHCP and if not, what is the best way?

Question

I have just set up a new Ubuntu server and I am going to be doing a lot of networking tests.

During setup, I simply skipped the network step.

I now need to switch between DHCP and an address quite often.

I know I can easily give a port an address via ifconfig eth0 x.x.x.x netmask x.x.x.x, but, is there an alternative that can be used in order to set a port to use DHCP?

If this isn't possible, I am guessing I can default in /etc/network/interfaces to dhcp and then just use up/down or restart networking in order to apply... but, I would much rather use ifconfig.

@TheX - I am just using Ubuntu Server, I am not actually "serving" anything! I need to switch between DHCP on one network and plugging on to another network where there is no DHCP server and there is a completely different range. — wilhil, Apr 23 '12 at 14:02
@TheX - Sorry... This is for downloading data/tests from one network that does have DHCP enabled... and then switching over to another network where there isn't DHCP. — wilhil, Apr 23 '12 at 14:10
@TheX - I'm sorry, I am not sure if there is something you haven't understood... I know exactly that this is the case! This is why I want to have a static IP and DHCP, and switch between them! In Windows, when testing networks, I just right click on the connection and put in an IP configuration and to get back to DHCP, I just tick the automatically assign box... I just want the Linux variation of that. — wilhil, Apr 23 '12 at 20:41
Oh... I see.. so you are just looking for an easy way to toggle it... — TheXed, Apr 23 '12 at 20:42
"TheX - Precisely! Sorry if I didn't explain, but, I didn't think it was that complicated! I can do this easily in GUI Linux which is very similar to Windows - I just can't figure out how to do it from the command line. — wilhil, Apr 23 '12 at 21:24

score 39 · Accepted Answer · edited Nov 17 '15 at 23:02

39

Change from static to dynamic

ifconfig eth0 0.0.0.0 0.0.0.0 && dhclient

Change back

killall dhclient && ifconfig eth0 10.0.1.22 netmask 255.255.255.0

edited Nov 17 '15 at 23:02

Community

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answered Apr 23 '12 at 13:58

RobotHumans

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you might need an ip route add as well – RobotHumans Apr 23 '12 at 14:08
Exactly what I need, thank you. But why to provide 0.0.0.0 ? dhclient alone worked for me. – 3bdalla Mar 08 '15 at 09:34
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It's a habit. So you're saying "unassign whatever address I currently have, then ask for an address" instead of just "ask for an address" – RobotHumans Mar 08 '15 at 11:28
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The `dhclient` should have the interface after it, too, because when the device after `ifconfig` isn't `eth0`, you need to specify it. – Jim Hunziker Dec 21 '15 at 17:20
If `dhclient` is already running, do we need to run it again? – logidelic Feb 13 '19 at 15:24
Yes, you do. It doesn't dynamically pick up new interfaces. – RobotHumans Feb 13 '19 at 15:30
Thank you @RobotHumans . And for the flipside of the question: Do you need to kill it when going static? What if it's required for other interfaces that are still DHCP? – logidelic Feb 14 '19 at 19:36
You don't HAVE to, but it might be a good idea to run it explicitly per interface in the many interfaces case. – RobotHumans Feb 14 '19 at 21:38

Is it possible to use Ifconfig to switch an interface to DHCP and if not, what is the best way?

1 Answers1