[rhelv6-list] dhclient running TWICE during boot (RHEL 6.2)

[Paul Smith]

Hi all; I have a number of up-to-date RHEL 6.2 systems and on all of
them I'm seeing a strange issue.  I have configured my network interface
(using NetworkManager GUI tool) to use DHCP to obtain an IP address.
I've also added DHCP_HOSTNAME=myhost to the ifcfg-Auto_eth0 file so that
the DNS values are updated for that hostname properly.

My DHCP system is configured to handle this properly and indeed it works
fine.

Here's the problem: during the boot of the system, dhclient is invoked
TWICE for the same network interface.  Each of these requests obtains
its own lease, but for some reason they both get DIFFERENT IP addresses.
This happens on all the systems that I've checked (I can see they all
have two lease files in /var/lib/dhclient and these lease files have
different IP addresses).

For some systems it all works out in the end and the interface and the
DNS server end up using the same IP address.  For other systems, the
network interface ends up using the other IP address, not the one that
the DNS server is using!  Maybe it's a timing thing?

I've tricked out one of my systems by renaming the dhclient binary and
replacing it with a shell script that generates debugging information
and then invokes the real dhclient.

I can see that the first invocation of dhclient is performed by rc via
S10network.  This one uses the default configuration of dhclient which
runs the dhclient-script and creates a lease file
/var/lib/dhclient/dhclient-eth0.leases.

The second invocation is performed by Networkmanager.  This one uses a
special-crafted configuration of dhclient which runs the
nm-dhcp-client.action command and creates a lease file
/var/lib/dhclient/dhclient-$UUID-eth0.leases, where $UUID is the value
of the UUID variable set in the
/etc/sysconfig/network-scripts/ifcfg-Auto_eth0 file.


I don't understand why this is happening: if NetworkManager is going to
manage the interfaces, why does the network script also do it?  I don't
know why I get two different IP addresses for the same interface, with
the same MAC, either but if I could solve the first problem so that only
one dhclient was run, presumably everything would work.  I'd prefer to
keep the NetworkManager configuration because that's how the users want
to manage their network interface (via the graphical tool).

Can anyone explain how this is supposed to work and where I've gone
wrong?  Do other people see duplicated lease files for the same
interface when using DHCP?