[Bug 1083565] [NEW] network-manager should not allow a computer to access the same network by both wired and wireless - this especially breaks Bonjour/mDNS

[Till Kamppeter]

Public bug reported:

I have a router making up one local NAT network connected to the
internet. The router allows to connect both wired and wireless. My
laptops are configured to use both wired and wireless. So I can walk
around with them and also connect to the quicker wired network if they
are on the desk.

Problem is that when the laptops are on my desk and I plug in the
network cables they stay connected on wireless and so they get connected
twice, wired and wireless, with two IP addresses, appearing as two
computers for the router and all other computers in the network. Most
things still simply work, like accessing the internet from the laptops,
SSHing to another computer, ... what causes problems is Bonjour/mDNS.
Avahi broadcasts available services (I have shared CUPS printers on the
laptops) into the network, using the host name of the machine assigned
on installation, for example "till-lenovo". As the broadcasts go through
two interfaces there is a service name conflict and it seems that Avahi
tries to overcome it by using host names like "till-lenovo-1", "till-
lenovo-2", ... When the laptop keeps running one sees in the "avahi-
discover" output on another machine the entries from the laptop, but
with host names (and so the service names) changing from time to time.
This leads to a client with a print queue pointing to a printer shared
by the laptop via the printer's Bonjour service name cannot print any
more.

I have done a short test and Avahi stops adding numbers to the original
host name when turning off wireless on the laptop so that it connects
only through the wired network.

One way of fixing (or working around?) the problem would be a change in
network-manager to automatically turn off wireless if the computer is
connected to a wired network and switching wireless back on when the
network cable gets disconnected. This would probably also solve problems
with other server functionality.

Another solution would be a change in Avahi, somehow recognizing that
the broadcasts through the two interfaces come from the same computer
and so they can (and should) have the same service names, or recognizing
that the two interfaces go into the same network and therefore broadcast
only through one of them, stopping the broadcasting through the weaker
one (the wireless in our case).

** Affects: avahi (Ubuntu)
     Importance: High
         Status: New

** Affects: network-manager (Ubuntu)
     Importance: High
         Status: New

** Also affects: avahi (Ubuntu)
   Importance: Undecided
       Status: New

** Changed in: avahi (Ubuntu)
   Importance: Undecided => High

** Changed in: network-manager (Ubuntu)
   Importance: Undecided => High

** Changed in: avahi (Ubuntu)
    Milestone: None => ubuntu-13.04-feature-freeze

** Changed in: network-manager (Ubuntu)
    Milestone: None => ubuntu-13.04-feature-freeze

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https://bugs.launchpad.net/bugs/1083565

Title:
  network-manager should not allow a computer to access the same network
  by both wired and wireless - this especially breaks Bonjour/mDNS

Status in “avahi” package in Ubuntu:
  New
Status in “network-manager” package in Ubuntu:
  New

Bug description:
  I have a router making up one local NAT network connected to the
  internet. The router allows to connect both wired and wireless. My
  laptops are configured to use both wired and wireless. So I can walk
  around with them and also connect to the quicker wired network if they
  are on the desk.

  Problem is that when the laptops are on my desk and I plug in the
  network cables they stay connected on wireless and so they get
  connected twice, wired and wireless, with two IP addresses, appearing
  as two computers for the router and all other computers in the
  network. Most things still simply work, like accessing the internet
  from the laptops, SSHing to another computer, ... what causes problems
  is Bonjour/mDNS. Avahi broadcasts available services (I have shared
  CUPS printers on the laptops) into the network, using the host name of
  the machine assigned on installation, for example "till-lenovo". As
  the broadcasts go through two interfaces there is a service name
  conflict and it seems that Avahi tries to overcome it by using host
  names like "till-lenovo-1", "till-lenovo-2", ... When the laptop keeps
  running one sees in the "avahi-discover" output on another machine the
  entries from the laptop, but with host names (and so the service
  names) changing from time to time. This leads to a client with a print
  queue pointing to a printer shared by the laptop via the printer's
  Bonjour service name cannot print any more.

  I have done a short test and Avahi stops adding numbers to the
  original host name when turning off wireless on the laptop so that it
  connects only through the wired network.

  One way of fixing (or working around?) the problem would be a change
  in network-manager to automatically turn off wireless if the computer
  is connected to a wired network and switching wireless back on when
  the network cable gets disconnected. This would probably also solve
  problems with other server functionality.

  Another solution would be a change in Avahi, somehow recognizing that
  the broadcasts through the two interfaces come from the same computer
  and so they can (and should) have the same service names, or
  recognizing that the two interfaces go into the same network and
  therefore broadcast only through one of them, stopping the
  broadcasting through the weaker one (the wireless in our case).

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