[CALUG] Random Network Interfaces

[Bryan J Smith]

From: Rajiv Gunja <opn.src.rocks at gmail.com>
>>>> Guess you did not read what I wrote. In all the above Operating Systems, 
>>>>irrespective of the platform, the hardware name once assigned will not change 
>
>>>>unless you move the physical location of the network card or peripheral, on 
>>>>their respective bus. This is true even on convexOS and OSF/1.

Correct.

>>>> By the way, Linux distros are available on SPARC, IA-64, MIPS and POWER 
>>>>platforms and it behaves exactly the same way. Granted that each platform will 
>>
>>>>have its own way of naming the peripheral depending the driver and kernel 
>>>>module.

On non-PC Linux, almost always correct.  Linux just handles the standards of 
OpenBoot, EFI64, ARC, etc... which are far more exacting than the PC BIOS.

But the PC BIOS is another story.

>>>> What in the world does "_not_control" mean? OSes do not control the hardware. 
>>
>>>>OSes are interfaces to the hardware. Kernel of each OS scans the hardware in 

>>>>whatever order and presents it to the OS/applications. Yes there are helpers to 
>>>
>>>>each platform: eeprom, bios, etc. But the underlying principle is the same.

But the hardware-firmware _does_ enumerate order.  Many times the 
hardware-firmware enumeration done by the PC BIOS does _not_ match the OS 
enumeration.

That's because the PC BIOS lacks standards.

>>>> Same thing goes for EFI, it too is an interface for the underlying hardware. If 
>>>>
>>>>the OS is EFI aware, then it makes use of it. Of course that seems redundant as 
>>>
>>>>none other than OSX seem to use it at the moment.

I've been running Linux on EFI -- PC, not IA-64 -- for a couple of years now.  
;)
It has its own maturity issues, but at least got some "shakedown" from IA-64.
Mac has shipped both EFI32 and EFI64, which is another issue I've run into.

>>>> Isn't that what I said? each OS will perform a scan in a certain order and that 
>>>>
>>>>remains constant, that is why we were able to install images on our Dell servers 
>>>>
>>>>without having to look at each hardware to see if the OS assigned eth0 or eth2 
>>
>>>>for the first network interface. (Solaris eeprom scans the last bus first) 

No, it is _not_ always constant with the PC BIOS.  I can_not_ emphasize this 
enough.

The way Fedora-based distros maintain eth# assignment is by MAC address in the 
"ifcfg-*" files.

But if you boot a kernel without network configuration, such as during 
Anaconda's install, it is not uncommon for different orders to re-occur, let 
alone the primary MAC (used to PXEBoot) may not match what is enumerated as 
eth0, etc...  This is especially the case if you change select details in the PC 
BIOS.

Unlike other platforms, it is not unheard of for re-order of devices on the 
PCI/PCI-X/PCIe bus in the PC BIOS, especially when a NVRAM change is made.  
Again, boot any Linux installer or without configuration files and you'll run 
into it.  ;)

>>>> I would not suggest changing mac address, unless you are sure that there will 
>>
>>>>be no other machine with the same address. Plus I do not see a point to changing 
>>>>
>>>>mac address, as it is unique to each network card manufactured around the 
>>>world.

I'm not changing MAC addresses in those files.  The ifcfg-* files assign "eth#" 
based on MAC address.  ;)

Otherwise, if one does not tie the MAC address to an eth# device, there is a 
chance of a re-assignment.  This is especially true when the MAC order may not 
match BIOS order, especially for things like PXEBoot.

It's not uncommon for the first MAC to PXEBoot, and then an installer to be 
confused as it comes up eth1.  That's why parameters have to be passed, MAC 
addresses entered in ifcfg-* files after installation, etc...




 -- 
Bryan J  Smith       Professional, Technical Annoyance 
Linked Profile:     http://www.linkedin.com/in/bjsmith 
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