[Bug 1541544] Comment bridged from LTC Bugzilla

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------- Comment From thorsten.diehl at de.ibm.com 2016-02-05 10:37 EDT-------
Hi Dimitri,

well done, your investigation and research! Thank you that you took the
time to dig deeply into that, even into kernel code. Great work!

Here my answers:

IIRC the kernel has for the qeth module layer2=1 set as the default. To
use layer3 (layer2=0), it needs to be set explicitely. Which means, if
noone changes the sysfs entry for layer2, layer 2 will be used as
default. For some setups it might be required to have layer3, thus it is
mandatory to ask.

An configuration check like for x64 arch will usually not work in a
mainframe/enterprise environment, may it be due to the lack of dhcp
server or to stringent firewalls.

And now to your last three questions:

Q1: ideally kernel and/or with udev assistance would do the autodiscovery of the required mode, if possible.
A1: yes, that would be preferable, but IIRC for qeth is is the user's responsibilty to choose the correct layer2 setting, according to the network admin's advice.

> Use this device in layer2 mode?
> The qeth network driver is used for OSA-Express cards, HiperSockets and similar devices.
> Using the card in layer2 mode will make it keep the MAC addresses of IPv4 packets.
> Alternative is to use layer3 mode, in that mode LLC headers are removed from incoming
> IPv4 packets. Incorrect mode will lead to lack of connectivity.
Q2: does the proposed new wording sound better to you? or how would you like the question to be worded?
A2: Yes, good and crispy wording! I totally agree, but please move the question "Use this device in layer2 mode?" to the end, as  it was before => and then it looks like this:
The qeth network driver is used for OSA-Express cards, HiperSockets and similar devices. Using the card in
layer2 mode will make it keep the MAC addresses of IPv4 packets. Alternative is to use layer3 mode, in that
mode LLC headers are removed from incoming IPv4 packets. Incorrect mode will lead to lack of connectivity.
Use this device in layer2 mode?

Q3: should I keep layer2 as default?
A3: yes, please. It is for almost all cases the recommended layer mode.

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https://bugs.launchpad.net/bugs/1541544

Title:
  ubuntu-installer makes a contradictional statement regarding
  layer2/layer3

Status in debian-installer package in Ubuntu:
  New

Bug description:
  == Comment: #0 - Thorsten Diehl <thorsten.diehl at de.ibm.com> - 2016-02-03 12:05:19 ==
  When I configure a qeth OSA device, the installer asks for device type, device and protocol layer:

  Please choose the type of your primary network interface that you will need for 
   
  installing the Debian system (via NFS or HTTP). Only the listed devices are   
  supported.  
  Network device type:  
    1: ctc: Channel to Channel (CTC) or ESCON connection,      
    2: qeth: OSA-Express in QDIO mode / HiperSockets,      
    3: iucv: Inter-User Communication Vehicle - available for VM guests only,     
   
    4: virtio: KVM VirtIO,      
  Prompt: '?' for help> 2
  2  
    
  Please select the OSA-Express QDIO / HiperSockets device.  
  Device:  
    1: 0.0.f5f0-0.0.f5f1-0.0.f5f2  [*],  
  Prompt: '?' for help, default=1> 1
  1  
    
  By default OSA-Express cards use layer3 mode. In that mode LLC headers are   
  removed from incoming IPv4 packets. Using the card in layer2 mode will make it
  keep the MAC addresses of IPv4 packets.  
  Use this device in layer2 mode?  
    1: Yes [*]  2: No  
  Prompt: '?' for help, default=1> 

  The last question experienced a change according to https://bugs.launchpad.net/ubuntu/+source/s390-netdevice/+bug/1526801
  Layer2 is the default, which is correct, since the qeth driver uses layer2 as default as well.

  However, the introductional text says: "By default OSA-Express cards
  use layer3 mode."

  And this is wrong and needs to be fixed. Correct wording is:

  "By default OSA-Express cards use layer2 mode. In layer3 mode LLC headers are   
  removed from incoming IPv4 packets. Using the card in layer2 mode will make it   
  keep the MAC addresses of IPv4 packets."

  == Comment: #2 - Thorsten Diehl <thorsten.diehl at de.ibm.com> - 2016-02-03 12:08:52 ==
  Although LP 1526801 deals with this subject, it is different.
  LP 1526801 is implemented and closed. Now the documentational part in the installer needs to follow that. Thus I recommend to treat this as a separate bug.

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