Re: ethernet connection

[Bjørn Mork <bjorn mork no>]

José Queiroz via networkmanager-list <networkmanager-list gnome org>
writes:

> I don't see any use of such feature. As long as both connections are
> DHCP-based, you don't need to bother where you are.

Well, there are use cases where this feature might be useful. It's
enough that only one of your sites require static addressing, without a
DHCP server.

FWIW, I used the scripts in the "laptop-net" Debian package for a number
of years to get exactly this functionality.  At the time I often used my
laptop in places where a DHCP server wasn't an option.  Typically
"borrowing" a spare ip address and switch port in a data centre for
temporary access.  Configuring these addresses and associated policies
in laptop-net let me just plug in the ethernet cable without worrying
too much about which site I was at.

The "laptop-net" package is way outdated and long gone.  But you can get
the idea about the features from the docs and scripts in the old source:
https://launchpad.net/ubuntu/+archive/primary/+sourcefiles/laptop-net/2.26-6/laptop-net_2.26.orig.tar.gz

The "IP Map File" section from doc/laptop-net.texi describes the
an interesting feature, which I believe is missing in NetworkManager:

  Laptop-net has the ability to automatically choose the scheme by
  probing the network.  This is accomplished by associating one or more
  @acronym{IP} addresses with some or all of your schemes.  When the
  computer is connected to a network, it probes the network to see which
  of the @acronym{IP} addresses are located on the local subnet.  If one
  of the @acronym{IP} addresses is found, the associated scheme is
  selected.

Pretty simple and working everywhere, assuming you can accept active
arp probing and filter out proxy arps (just compare the answers for
multiple addresses).

Using LLDP, CDP or other L2 management protocols as additional input
parameters might be useful in some situations, but would not be
sufficient by itself.  These protocols are often disabled even when
supported. For good reasons.  If you can guarantee any of these, then
you might as well add a DHCP server..




Bjørn