[SOLVED] Operate eth0 and wlan0 interchangeably

crts · 09-11-2018, 02:45 PM

I tried to make WiFi on my notebook work by following the instructions at https://docs.slackware.com/slackbook:wifi. Of course, it does not work.
The problem seems to be that I am trying to operate the WiFi card AND the ethernet card interchangeably. Here is an excerpt of my rc.inet1.conf

Code:

IPADDR[0]="192.168.1.10"
NETMASK[0]="255.255.255.0"
...
IFNAME[1]="wlan0"
IPADDR[1]="192.168.1.15"
NETMASK[1]="255.255.255.0"
...
GATEWAY=192.168.1.1

Everything is working as long as the ethernet cable is plugged in. If I unplug then the network does not work, even though I can see at my router that wlan0 has registered correctly. Running route -n reveals

Code:

# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.1.1     0.0.0.0         UG    0      0        0 eth0
127.0.0.0       0.0.0.0         255.0.0.0       U     0      0        0 lo
...

Is there a way to route to the gateway via wlan0? The only disadvantageous solution I have so far is to configure only wlan0, e.g.,

Code:

IFNAME[0]="wlan0"
IPADDR[0]="192.168.1.15"
NETMASK[0]="255.255.255.0"
...
GATEWAY=192.168.1.1

but then I still have to reboot and if I do not need WiFi then eth0 will not work and I have to reconfigure again. There must be a better, smarter and faster way to reassign the gateway route, right?

PS: Please do not suggest any kind of network manager, like wicd or NetworkManager etc. Thanks.

abga · 09-11-2018, 03:02 PM

This might interesting for your scenario:
https://www.linuxquestions.org/quest...er-4175637284/

crts · 09-11-2018, 03:17 PM

No, I actually want the interfaces to have different addresses. I was thinking of a solution like

Code:

route add default gw 192.168.1.1 eth0

to switch back to eth0, but this just returns an error:

Code:

SIOCADDRT: Network is unreachable

I further noticed, that if I configure eth0 after wlan0 in rc.inet1.conf then eth0 does not get configured at all, not sure what the reasoning behind this behaviour is.

crts · 09-11-2018, 04:05 PM

As it turns out it is just as easy as simply running

Code:

route add default gw 192.168.1.1 [eth0|wlan0]

It did not work previously because while fiddling with rc.inet1.conf I misconfigured it accidently.

Follow up question: What is the equivalent 'ip' command for above 'route add ...'?

bassmadrigal · 09-11-2018, 04:11 PM

Quote:

Originally Posted by crts

Follow up question: What is the equivalent 'ip' command for above 'route add ...'?

I'd imagine:

Code:

ip route add default via 192.168.1.1 dev eth0

But this is just after looking at this cheatsheet, which doesn't cover specifying devices with that particular command.

abga · 09-11-2018, 04:16 PM

It'll be useful if you could specify what version of Slackware you're on.
Then, can you please provide the output of the following commands before you unplug the eth0 cable and afterwards?

Code:

/usr/sbin/ip link show
/usr/sbin/ip addres show
/usr/sbin/ip route

I'm not using the rc.inet* scripts Slackware is providing but my own (personal preference) and I don't know them very well (how they are configuring the interfaces) but from a networking POV, after you unplug the eth0 you'll also loose the default gateway. The commands from above will show that.

If you don't like the bonding/fail-over solution that I suggested in my previous post, there is another way to achieve what you're looking after, but some manual steps would be required. You need to define two default routes for your two adapters (eth0,wlan0) with different metrics.
Again, not really knowing how rc.inet1 is doing the config (too tired now to parse it), you might have the possibility to leave the GATEWAY= empty in rc.inet1.conf and insert these lines in the rc.inet1 script, where the default GW is defined:

Code:

/usr/sbin/ip route add default via 192.168.1.1 metric 1 dev eth0
/usr/sbin/ip route add default via 192.168.1.1 metric 11 dev wlan0

You could also put these two lines in rc.local, but that script is executed very late and you might need connectivity before that.

P.S. While I was writing my post you already discovered ip route