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Old 05-06-2011, 05:03 AM
Les Mikesell
 
Default RHEL 6.1 beta

On 5/5/11 11:34 PM, R P Herrold wrote:
> On Thu, 5 May 2011, Ljubomir Ljubojevic wrote:
>
>> I do not have personal experience with CentOS, but I have seen different
>> X86-PC MB's on embedded units/routers recognizing LAN and Wireless NIC's
>> differently ones from PCI1 to PCI5, others from PCI5 to PCI1, one MB
>> even without any order at all. I had now Monitor so I had to power the
>> unit, guess NIC to connect to, login and see what was recognized in what
>> order.
>
> Built from the sources that will become a CentOS 6 series,
> there is a more mature udev implementation, which tracks MAC
> addresses, and assigns them 'durably' to persist at a given
> device name. Debian testing supports a similar approach, but
> with more manual intervention
>
> I'll try to blog about it, but once one knows the 'secret' it
> is not all that hard to predict -- This unit has three NICs
> (two onboard of the same type and an addon) which do NOT
> 'wander around' through reboots

But can you swap the disk into a new chassis of identical hardware and have it
come up with the right subnets on the NICs in the corresponding physical
positions? Without knowing MAC addresses ahead of time?

--
Les Mikesell
lesmikesell@gmail.com
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Old 05-06-2011, 12:53 PM
R P Herrold
 
Default RHEL 6.1 beta

On Fri, 6 May 2011, Les Mikesell wrote:
herrold:

>> I'll try to blog about it, but once one knows the 'secret' it
>> is not all that hard to predict -- This unit has three NICs
>> (two onboard of the same type and an addon) which do NOT
>> 'wander around' through reboots

> But can you swap the disk into a new chassis of identical
> hardware and have it come up with the right subnets on the
> NICs in the corresponding physical positions? Without
> knowing MAC addresses ahead of time?

Not without prior knowledge of the MAC addresses and edits,
but it is still trivial to do. With DHCP fabric on a physical
segment, however, the devices will come up and be assigned
IPs, the MAC addresses discerned [hooray for 'arpwatch' to
make this trivial], and then may be revised into permanent
working assignments without the need to resort to ILO or such

Indeed the reason the udev rules segment quoted is in the the
rather peculiar order: eth2, eth1, eth0 ... is that I had done
just that kind of drive move, and prior to just such edits of
that file, it enumerated MAC address and associated them to
devices in order: eth0 eth1 eth2 eth3 eth4

I editted the file for the last two [not bothering to move
specification stanzas, as udev is indifferent to ordering],
and renamed the corresponding
/etc/sysconfig/networking-scripts/ifcfg-eth3 and ifcfg-eth4
into eth1 and eth0 respectively. Then within those two files,
I edited the DEVICE names to complete the move a disk from the
host it was built on, to the host it is now running on

The process is stable and predictable enogh that these edits
were done via just such a process, after a 'remote pair of
hands' had physiclly installed the drive into a chassis at a
datacenter that I cannot presently travel into and work at
comfortable, due to an ankle injury some months ago. The
'cold' aisles are too narrow for a stool or chair, and trying
to work standing one-legged like a stork is too tiring

-- Russ herrold
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Old 05-06-2011, 03:25 PM
Les Mikesell
 
Default RHEL 6.1 beta

On 5/6/2011 7:53 AM, R P Herrold wrote:
>
>>> I'll try to blog about it, but once one knows the 'secret' it
>>> is not all that hard to predict -- This unit has three NICs
>>> (two onboard of the same type and an addon) which do NOT
>>> 'wander around' through reboots
>
>> But can you swap the disk into a new chassis of identical
>> hardware and have it come up with the right subnets on the
>> NICs in the corresponding physical positions? Without
>> knowing MAC addresses ahead of time?
>
> Not without prior knowledge of the MAC addresses and edits,
> but it is still trivial to do. With DHCP fabric on a physical
> segment, however, the devices will come up and be assigned
> IPs, the MAC addresses discerned [hooray for 'arpwatch' to
> make this trivial], and then may be revised into permanent
> working assignments without the need to resort to ILO or such

Supplying DHCP service with spare addresses on a bunch of remote subnets
at a bunch of remote locations isn't really trivial just to be able to
have a centos box work there.

> The process is stable and predictable enogh that these edits
> were done via just such a process, after a 'remote pair of
> hands' had physiclly installed the drive into a chassis at a
> datacenter that I cannot presently travel into and work at
> comfortable, due to an ankle injury some months ago. The
> 'cold' aisles are too narrow for a stool or chair, and trying
> to work standing one-legged like a stork is too tiring

There are lots of reasons to want to be able to ship pre-loaded disks
separately from the chassis or have remote support swap either one. You
don't have to cast it as a rare circumstance. Consider the 'green'
value of shipping drives instead of whole machines (which is what we
usually end up doing for anything complicated). I just hope whatever
they are doing in 6.1 for non-random naming works on our hardware. On a
more practical note, I suppose I should have written something long ago
that runs automatically after network startup that parses the ifcfg-ethx
files, tries to ping the gateways through each interface and juggles
things around until it works at least on the subnet we use for
administration. I had something like that mostly working when I did a
'clonezilla image on dvd' rollout to upgrade a bunch of machines from a
centos3 to 5 base, but in that case I had the previous mac/IP's to work
with and was trying to match the old setup after the image came up on
each one. But, it failed on a few and I didn't bother to track the bugs
down because it would have been hard to reproduce the circumstances.

--
Les Mikesell
lesmikesell@gmail.com
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