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[Bug 811554] New: Troubles with ethernet+WLAN and NetworkManager
  • From: bugzilla_noreply@xxxxxxxxxx
  • Date: Tue, 26 Mar 2013 02:09:53 +0000
  • Message-id: <>

Summary: Troubles with ethernet+WLAN and NetworkManager
Classification: openSUSE
Product: openSUSE 12.3
Version: Final
Platform: x86-64
OS/Version: Other
Status: NEW
Severity: Normal
Priority: P5 - None
Component: Network
AssignedTo: bnc-team-screening@xxxxxxxxxxxxxxxxxxxxxx
ReportedBy: bernd.paysan@xxxxxx
QAContact: qa-bugs@xxxxxxx
Found By: ---
Blocker: ---

User-Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.32 (KHTML,
like Gecko) Chrome/27.0.1425.0 Safari/537.32 SUSE/27.0.1425.0

That probably should go upstream, but I report it here, too, just in case
somebody wants to dig into it.

Background: I'm testing handover for an experimental new protocol, and to do
so, I use the Ethernet and WLAN connection of my laptop. The handover of my
own protocol works fine (completely flawless, connection stays alive, flow
control adjusts to different bandwidth), but as I use UDP on IPv4/IPv6
(whatever is available) as underlying protocol, I have some troubles with
that... and it seems to be that nobody else is testing that sort of stuff. It
might be because TCP does not support handover... so changing a network
interface is disruptive when you use TCP, and therefore nobody wants this...

a) NetworkManager assigns the same metric for both WLAN and Ethernet, which
causes whoever is first in the list to be preferred when both are available.
That's just wrong, cable should be preferred, i.e. have a lower metric. The
metric is not configurable in NetworkManager, unless you manually add routes.

Fix: depending on interface class, add different metrics into NetworkManager,
and add syntax to the configuration files for different connections to allow
users to select the metric (not everybody might be happy with the default).

Workaround: Disable WLAN when you have Ethernet plugged in.

b) If you just enable WLAN and rip out the cable, routing for IPv4 on eth0 is
removed (reported by /sbin/route). But routing for IPv6 stays (reported by
/sbin/ip -6 route). Which is pretty confusing, as you can create new IPv4
connections over WLAN, but no IPv6 connections. I suppose that results from a
lack of testing IPv6.

Workaround: do an ifconfig eth0 down, this removes the routing quickly.

Reproducible: Always

Steps to Reproduce:
1. Attach both LAN cable and enable WLAN for a laptop
2. Check which connection is actually used
3. rip out the LAN cable and then do /sbin/ip -6 route
Actual Results:
sbin/ip -6 route
fd00::/64 dev eth0 proto kernel metric 256 expires 5054sec
fd00::/64 dev wlan0 proto kernel metric 256 expires 6819sec
fe80::/64 dev eth0 proto kernel metric 256
fe80::/64 dev wlan0 proto kernel metric 256

eth0 still is in the routing table for IPv6, both have the same metric (eth0
should be less than wlan0)

Expected Results:
/sbin/ip -6 route
fd00::/64 dev wlan0 proto kernel metric 256 expires 6758sec
fe80::/64 dev wlan0 proto kernel metric 256

Should have removed the eth0 device from the IPv6 routing table

I know that TCP won't give me a seamless transition from one route to the
other. But what I want is: plug in cable, have instantly faster network.
Unplug, have instantly slower WLAN. Connections stay alive. That requires
"fixing" TCP, and that's what I'm doing research at. NetworkManager still
needs some further fixing.

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