Also worked again this morning.

rolfie

pre-up ifdown wlan0 || true

to the eth0 configuration, and

pre-up ifdown eth0 || true

to the wlan0 configuration.

You must also remove the allow-hotplug lines to avoid that the automated management tries to bring them both up on boot and status change. Then bring the right one up manually, or via some software that understands the applicable cabling situation, like for example wicd, connman or network-manager.

Note that any of the latter will compete with your current networking setup, so you will need to clear that out if you use one of them.

Alternatively you take the DIY approach using ethtool and wpa_cli to discover the applicable cabling situation; this approach brings the great joy of further learning situations. (For example that  wlan0 must be brought up at link level without configuration in order to scan for access points and determine its "cabling" options, while eth0 is more physical)

Isn't there a tool that does this switching sort of automagically if configured accordingly? Or do I have to re-invent the wheel? Is any of the network managers of any use in this case?

I use Network Manager and in Cinnamon the Network applet would allow you to enable whichever of ethernet or wireless is enabled.
You can still confuse it by choosing both if both are enabled.
With a laptop you'd usually choose ethernet if you were sitting at a desk that was wired. Elsewhere you'd probably try and use Wireless.

auto eth0
iface eth0 inet static
	address 10.5.5.31/24
	gateway 10.5.5.1
	metric 10
	# dns-* options are implemented by the resolvconf package, if installed
	dns-nameservers 10.5.5.1
	dns-search lan.atHome

# WLAN @ Home
auto wlan0
iface wlan0 inet static
	address 10.5.5.32/24
	gateway 10.5.5.1
	metric 20
	dns-nameservers 10.5.5.1
	dns-search lan.atHome
	wpa-ssid 	SSID
	wpa-psk		passwd

The metric keyword assigns a priority to the interface, a lower metric value causes that interface to be favoured over the other.

Isn't there a tool that does this switching sort of automagically if configured accordingly? Or do I have to re-invent the wheel? Is any of the network managers of any use in this case?

Well, I think I need a break now for a day or so. My brain is confused by too many different posts describing differernt ways.

See you later alligator.

# ifdown eth0 ; ifup wlan0

Secondly, the gateway for static configuration does the same as your post-up additions to the wlan0 confguration; i.e. remove the post-up lines.

Thirdly, with allow-hotplug rather than auto you declare that networking should be managed via hotplugging, in which case udev will try to configure the nominated interfaces. Both of them if there is a cable, and potentially with a bit of race between them; one first, then the other. Since you have gateway declarations for both configurations, there will be a competition where the first one wins.

Possibly your misapprehension is that you regard the configurations as alternatives while udev will treat them as "complementary" or "conjunctive" and apply them both. Afaict the network management via either allow-hotplug (/lib/udev/net.agent) or auto (/etc/init.d/networking) don't actually detect "presence of cable" to only apply configurations "as per available cabling". Instead it will configure all interfaces that it is set to configure, i.e., both eth0 and wlan0, including the possible race and competition about gateway (aka default route).

The problem with 2 interfaces on the same network is that return traffic will go through the first unless you in addition set up a source based routing rule, so that the kernel has different routing tables for outbound packets depending on what the source IP is. That can be done, but it's not an automatic function in the kernel's networking logic.

Digging in the internet showed that routing must be the issue, and I found one or the other useful hint. I modified the /etc/network/interfaces like this:

# The primary network interface
allow-hotplug eth0
iface eth0 inet static
	address 10.5.5.31/24
	gateway 10.5.5.1
	# dns-* options are implemented by the resolvconf package, if installed
	dns-nameservers 10.5.5.1
	dns-search lan.atHome
	post-up ip route del default
	post-up ip route add default via 10.5.5.1 dev eth0

# WLAN @ Home
allow-hotplug wlan0
iface wlan0 inet static
	address 10.5.5.32/24
	gateway 10.5.5.1
	dns-nameservers 10.5.5.1
	dns-search lan.atHome
	wpa-ssid 	        SSID
	wpa-psk		passwd
	#up route add -net 10.5.5.0 netmask 255.255.255.0 gw 10.5.5.1 dev wlan0
	#down route delete -net 10.5.5.0 netmask 255.255.255.0 gw 10.5.5.1 dev wlan0
	post-up ip route del default
	post-up ip route add default via 10.5.5.1 dev wlan0

After a # service networking --full-restart I could ping the DSL modem and use FF to call up some pages.

Today the wifi does not really like to start up. I can get it to start up by a series of ifup wlan0 and ip link set wlan0 up, but I haven't found a clue why its not working sometimes. Also restarting the service fails, and the route always is via eth0.

Errors I am getting:
On ifup I get RTNETLINK: file exists, failed to bring up wlan0.
On the restart of the service I get: wpa_supplicant daemon failed to start, exited with return code 1.

I am a bit exhausted in the moment.

rolfie

BTW: is there a toolkit that allows to use the functions keys of the laptop that are triggered by FN-Fx under Windows in the same way in Debian/Devuan?

# ip route replace default via 10.5.5.1 dev wlan0

You also should rather not have localnet routes to 0.0.0.0; it doesn't really matter since the first matching rule (via wlan0) is used shadowing the other but it may bring confusion to the mind of the operator.

EDIT: actually I got confused; those are the "normal" net routes... but you should probably avoid net routes to unconnected interfaces. Remember that when there are multiple routes of same specificity, then the first in the list will be used.

I don't want to switch my complete home network from static to dynamic adresses right now

You can set specific address with a DHCP client.

I've never tried having both ethernet and wireless configured via /etc/network/interfaces and my Debian system is gone now so I can't fiddle with it to test what works (sorry).

If you're using chimaera then perhaps try iwd for the wireless connection. That can both associate with the SSID and assign the IP addresses all by itself.

Yes, can confirm this. BUUUT: when I remove the gateway definition in the wlan0 section, I can't get the interface to wake up again. Has cost me several minutes not to say hours now. So I have the message back and the wlan0 at least being recognised agaion by the router. Also I have looked a bit deeper into the routing issue and found one or the other bit of information in the internet. Unfortunatley, a lot of the stuff seems to be outdated, syntax no more correct .....

Made a little step forward by adding a route for wlan0:

route add -net 10.5.5.0 netmask 255.255.255.0 gw 10.5.5.1 dev wlan0
# route
Kernel-IP-Routentabelle
Ziel            Router          Genmask         Flags Metric Ref    Use Iface
default         fritz.box       0.0.0.0         UG    0      0        0 eth0
localnet        fritz.box       255.255.255.0   UG    0      0        0 wlan0
localnet        0.0.0.0         255.255.255.0   U     0      0        0 eth0
localnet        0.0.0.0         255.255.255.0   U     0      0        0 wlan0
link-local      0.0.0.0         255.255.0.0     U     1000   0        0 eth0

Now a few pings do work:

# ping -c 3 10.5.5.1
PING 10.5.5.1 (10.5.5.1) 56(84) bytes of data.
64 bytes from 10.5.5.1: icmp_seq=1 ttl=64 time=6.15 ms
64 bytes from 10.5.5.1: icmp_seq=2 ttl=64 time=6.77 ms
64 bytes from 10.5.5.1: icmp_seq=3 ttl=64 time=4.38 ms

--- 10.5.5.1 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2004ms
rtt min/avg/max/mdev = 4.384/5.768/6.770/1.010 ms
# ping -c 3 8.8.8.8 
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
From 10.5.5.31 icmp_seq=1 Destination Host Unreachable
From 10.5.5.31 icmp_seq=2 Destination Host Unreachable
From 10.5.5.31 icmp_seq=3 Destination Host Unreachable

--- 8.8.8.8 ping statistics ---
3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2050ms
pipe 3
# ping google.com -c 3
PING google.com(fra16s56-in-x0e.1e100.net (2a00:1450:4001:82f::200e)) 56 data bytes
64 bytes from fra16s56-in-x0e.1e100.net (2a00:1450:4001:82f::200e): icmp_seq=1 ttl=119 time=19.3 ms
64 bytes from fra16s56-in-x0e.1e100.net (2a00:1450:4001:82f::200e): icmp_seq=2 ttl=119 time=18.4 ms
64 bytes from fra16s56-in-x0e.1e100.net (2a00:1450:4001:82f::200e): icmp_seq=3 ttl=119 time=20.4 ms

--- google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2004ms
rtt min/avg/max/mdev = 18.355/19.366/20.437/0.850 ms
# ping www.spiegel.de -c 3
PING aacfb9d106f4.link11.de (128.65.210.180) 56(84) bytes of data.
From rh031.lan.beiHeinrichs (10.5.5.31) icmp_seq=1 Destination Host Unreachable
From rh031.lan.beiHeinrichs (10.5.5.31) icmp_seq=2 Destination Host Unreachable
From rh031.lan.beiHeinrichs (10.5.5.31) icmp_seq=3 Destination Host Unreachable

--- aacfb9d106f4.link11.de ping statistics ---
3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2056ms
pipe 3

As it looks like now I can ping the DSL router, and a few things work on the internet. Strangely enough the 8.8.8.8 did not work, while google.com was resolved. Also tried to call up the magazine Spiegel with Firefox, adress isn't resolved. No idea why not.

Something still isn't right.

Also tried to add some routing ruies to the interfaces file, does not seem to work as expected.

Where do I need to go from here?

rolfie

Try using DHCP for the wireless interface.

EDIT: I presume wpa-sssid & wpa-psk have the actual SSID & password filled in (rather than SSID & passwd)?

Yes, I have removed the real contents and replaced it with dummy data. As I mentioned, the DSL router (a AVM Fritzbox 7580) sees my laptop (after some struggle) and also tells me which frequency the laptop is using. Also the IP is present.

rolfie

# rfkill list all
0: hci0: Bluetooth
	Soft blocked: no
	Hard blocked: no
1: acer-wireless: Wireless LAN
	Soft blocked: no
	Hard blocked: no
2: acer-bluetooth: Bluetooth
	Soft blocked: no
	Hard blocked: no
3: phy0: Wireless LAN
	Soft blocked: no
	Hard blocked: no

Seems I am also having issues with powersave, and I have no idea how to wake up the wifi when its sleeping. After a fresh reboot:

# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
    link/ether b4:a9:fc:f0:49:e9 brd ff:ff:ff:ff:ff:ff
    inet 10.5.5.31/24 brd 10.5.5.255 scope global eth0
       valid_lft forever preferred_lft forever
3: wlan0: <BROADCAST,MULTICAST> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
    link/ether 94:08:53:88:fe:3f brd ff:ff:ff:ff:ff:ff
    inet 10.5.5.32/24 brd 10.5.5.255 scope global wlan0
       valid_lft forever preferred_lft forever
# ip link set wlan0 up
# ifup wlan0
RTNETLINK answers: File exists
ifup: failed to bring up wlan0
# ip link set wlan0 up
# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
    link/ether b4:a9:fc:f0:49:e9 brd ff:ff:ff:ff:ff:ff
    inet 10.5.5.31/24 brd 10.5.5.255 scope global eth0
       valid_lft forever preferred_lft forever
3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 94:08:53:88:fe:3f brd ff:ff:ff:ff:ff:ff
    inet 10.5.5.32/24 brd 10.5.5.255 scope global wlan0
       valid_lft forever preferred_lft forever
    inet6 fe80::9608:53ff:fe88:fe3f/64 scope link tentative 
       valid_lft forever preferred_lft forever
# ip r
default via 10.5.5.1 dev eth0 onlink linkdown 
10.5.5.0/24 dev eth0 proto kernel scope link src 10.5.5.31 linkdown 
10.5.5.0/24 dev wlan0 proto kernel scope link src 10.5.5.32 
169.254.0.0/16 dev eth0 scope link metric 1000 linkdown 
# ping -c 3 10.5.5.1
PING 10.5.5.1 (10.5.5.1) 56(84) bytes of data.
From 10.5.5.31 icmp_seq=1 Destination Host Unreachable
From 10.5.5.31 icmp_seq=2 Destination Host Unreachable
From 10.5.5.31 icmp_seq=3 Destination Host Unreachable

--- 10.5.5.1 ping statistics ---
3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2054ms
pipe 3
# ping -c 3 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
From 10.5.5.31 icmp_seq=1 Destination Host Unreachable
From 10.5.5.31 icmp_seq=2 Destination Host Unreachable
From 10.5.5.31 icmp_seq=3 Destination Host Unreachable

--- 8.8.8.8 ping statistics ---
3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2034ms
pipe 2
# ping -c 3 google.com
ping: google.com: Temporärer Fehler bei der Namensauflösung

Directly after the reboot the wifi is down. I have to wake it up, then the 5G connection is opened.

The if r brings an interesting fact to daylight:

169.254.0.0/16 dev eth0 scope link metric 1000 linkdown

What is that? I am sure I never set this anywhere.

Edit: found an entry in the /etc/networks file: link-local 169.254.0.0. There are also some entries in /etc/network/-subdirs that refer to avahi. The scripts also contain a reference to these adresses.

Somewhere a route is specified that does only work with eth0.

Suggestions?

Rolf

ip a
ip r
ping -c3 8.8.8.8
ping -c3 google.com
rfkill list all

EDIT: I presume wpa-sssid & wpa-psk have the actual SSID & password filled in (rather than SSID & passwd)?