[Bug 713385] Re: netcfg/choose_interface=auto fails to find the right interface

[Chuan Li]

One of UA customer runs into this issue at 20.04. 
The customer is not using PXE boot to install server. The customer is using a customized ISO to install the server, so the comment #18 is not applicable.

For example, the preseed is like

d-i netcfg/choose_interface select auto
d-i netcfg/disable_autoconfig boolean true
d-i netcfg/get_ipaddress string 10.x.x.x
d-i netcfg/get_netmask string 255.255.255.224
d-i netcfg/get_gateway string 10.x.x.x
d-i netcfg/get_nameservers string 10.x.x.x
d-i netcfg/confirm_static boolean true 


When the server has multiple interfaces but only one interface is connected, the 'auto' can not recognize the right one. 
The workaround is to select the right one manually as 'd-i netcfg/choose_interface select eno5'.

But if different machines have different interfaces being connected, the
customized ISO will need to be constantly modified accordingly.



** Tags added: sts

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https://bugs.launchpad.net/bugs/713385

Title:
  netcfg/choose_interface=auto fails to find the right interface

Status in netcfg package in Ubuntu:
  Confirmed

Bug description:
  Binary package hint: netcfg

  Under some circumstances, netcfg may not be able to find the right
  interface to run dhclient on when netcfg/choose_interface is set to
  auto.  It looks like the way choose_interface=auto works is that
  ethtool finds the lowest numbered interface that reports a link, and
  runs dhclient on that interface.  If no interface with a link is
  found, it tries only eth0.

  I'm hitting a problem on a number of servers that have one or two
  Broadcom BCM5708 interfaces *and* two Intel gigabit interfaces.  If
  the network connection is plugged in to the BCM5708, the install will
  often fail to find a network with netcfg/choose_interface=auto.

  The problem is that the BCM5708 doesn't report link up until you try
  to send traffic over it.  So none of the interfaces on the server
  report having a link, and netcfg tries dhcp on just eth0.  Depending
  on the order the network modules have been loaded, eth0 may be the
  BCM5708 or it may be the Intel.  If eth0 is the Intel, d-i attempts to
  run dhclient on the wrong interface, and it fails.

  I think a reasonable solution to this problem would be for netcfg to
  attempt dhclient on all interfaces until one succeeds.  Or perhaps it
  should do this only when no interfaces report a link.  Either way, I
  don't think we can rely entirely on link status, because not all NIC
  report this correctly.

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