Ubuntu – How to make dhclient forget its last DHCP lease

dhcpnetwork-managernetworking

What I'm trying to achieve is to get cold-start, zero-state DHCP lease which means forcing dhclient through the full discovery and configuration process (DHCPDISCOVER–DHCPOFFER–DHCPREQUEST–DHCPACK as opposed to the shortcutted DHCPREQUEST–DHCPACK cycle which uses a remembered address). I need this to debug a network configuration problem.

I have tried:

flushing current lease with dhclient -r, disconnecting the current Network Manager connection;
killing any leftover dhclient and dnsmasq processes;
cleaning /var/lib/dhcp/ directory, which supposedly contains the client lease database;
sudo restart network-manager.

But even after these steps I see in the logs DHCPDISCOVER immediately followed by DHCPREQUEST of somehow still remembered address.

Clearly, the OS is storing the address somehow else, and I've run out of ideas. Any help from the community?

Best Answer

This did the trick for me(for eth0, run from sudo su):

dhclient -r -v eth0 && rm /var/lib/dhcp/dhclient.* ; dhclient -v eth0

Related Solutions

Ubuntu – How does dhclient get called under 12.04

This ended up being caused by network-manager. My /etc/NetworkManager.conf file looked like this :

[main]
plugins=ifupdown,keyfile
dns=dnsmasq

[ifupdown]
managed=false

This config file was set like this when the machine was built (this may be a bug). By the fact that "managed" was set to false, NetworkManager wasn't initiating dhclient for the interface, and it wasn't considering the wired connection to be a real connection and so it wouldn't initiate the VPN either.

I changed "managed" to "true" and restarted the system. It works just as I'd hope now, runs dhclient, VPN works etc.

And to answer some of my own questions :

This is what the wired connection tab in a standard NetworkManager Network Connections dialog should look like : http://i.imgur.com/TgUs8.png
dhclient is kicked off my NetworkManager and then stays running while the connection is up

Ubuntu – How to configure dhcp to always assign from the lowest unused ip

As suggested by Melebius, the dhcp server in my scenario is not actually in the Ubuntu instance (vm guest) - it was simply a virtualized component (or "part of the virtualization program") on the host machine, with some configurable options. Even if I could configure it, it would have been independent of Ubuntu.

Hence, the workaround using dhcp-requested-address with dhclient seems to be the best option in this situation, with minimal change to a default installation.

Best Answer

Related Solutions

Ubuntu – How does dhclient get called under 12.04

Ubuntu – How to configure dhcp to always assign from the lowest unused ip

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