>>> On 11/24/2011 at 09:59 AM, Agblad Tore <[email protected]> wrote:
> Hi again.
> I have these tricky things showing up all the time :)
> I have looked here and there but I don't find the answer to this question:
>
> /etc/udev/rules.d contains rules, but as they have persistent in the name I
> get suspicious.
> and I don't fully understand how these rules are used and when
All udev rules are used when the kernel generates "events" that udev listens
for and then processes. The "persistent" in the name means that those rules
will ensure that a given device will be given the same name across a reboot.
In the past, that was not guaranteed, so during one boot, a NIC could be eth0,
and the next eth1, and so on.
> When a RHEL6 starts and activates the network adapter, does it know if it is
> layer 2 or 3 and
> is that info used to update /etc/sysconfig/network-scripts/ifcfg-eth0 ?
I doubt it very much. Typically, the "knowledge" of whether a NIC is layer 2
or 3 is provided by whomever does the installation, and the installer records
that in ifcfg-eth?, or in the udev rules (depending on what level of the OS
you're running) for future reference. For example, on my SLES11 guest, I have
a /etc/udev/rules.d/51-qeth-0.0.0800.rules, and inside is this line (among many
others):
ACTION=="add", SUBSYSTEM=="ccwgroup", KERNEL=="0.0.0800", ATTR{layer2}="1"
My /etc/sysconfig/network/ifcfg-eth? file does _not_ have any reference to
layer2 at all.
-snip-
> Maybe we will switch to layer 2 later, and if so we want the servers to
> automagically configure itself.
I would strongly recommend that any such change should be made manually, not
automatically. Too much potential for problems.
Mark Post
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