[CALUG] Random Network Interfaces

[jecottrell3 at comcast.net]

This is totally unrelated, but it makes a good story.

Last year I was building servers in a rack and found out that altho the NICs are numbered 0 thru 3 on the chassis, Linux calls NIC 0 "eth2".

The only way i found this out was by ifconfig'ing each interfact up individually until one worked. I'm not sure what the rest of the mapping are.

The reason for this is most likely that there are actually two different type of ethernets, each with two ports, and the devices are probed in a differrent order than SUn (it's a SunFire X4200) would do it.

JIM

----- Original Message -----
From: "Jim Bauer" <jfbauer at comcast.net>
To: calug at unknownlamer.org
Sent: Wednesday, March 23, 2011 6:58:50 AM
Subject: Re: [CALUG] Random Network Interfaces

On 03/22/2011 11:32 PM, Randal T. Rioux wrote:
> Greetings.
>
> I haven't used Linux as a router/firewall in 15 years. Usually use
> OpenBSD or dedicated appliances. I wanted to give RHEL6 a shot and
> experienced some oddities.
>
> I've also tested this with Slackware 13.1 for the record.
>
> I have 8 NICs on an IBM x345. With OpenBSD, I can reboot and switch
> cables and networks and the NIC devices are always named the same.
>
> Doing the same with RHEL and Slackware keeps
> incrementing/adding/removing eth's each time (messing up IP assignments
> and causing general mayhem), i.e. eth0 because eth3, eth5 is gone, etc.
>
> Is this a feature? Can somebody explain this to me? My Web search foo
> must be weak this evening.
>

This might be the same thing I noticed a while back with ubuntu when I 
replaced some ancient network cards with something more modern and the 
eth numbers all changed (except for the one card I left in place).  I 
tracked it to udev.  It remembers the MAC addresses and if eth0 had 
01:02:03:04:05:06 then eth0 will always have that mac address.  So it 
you replace that card with another, the new card will get the next 
available ethN.  And if you ever put back that old card, it'll reappear 
as eth0.  I believe /etc/udev/rules.d/70-persistent-net.rules is where 
that is recorded.


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