I am running Ubuntu 16.04. I have a pretty simple networking setup, a router with both wifi and wired connections. Separately I can connect to the router using either wifi or ethernet and both work well reliably. However, when I have both connected at the same time, the internet stops working and pages stop loading. I have tried looking up a similar question online, but most of the folks are trying to connect to connect to different networks. My situation seems pretty basic but I have been unable to find a solution. Any help is very much appreciated.
Working LAN Only:
$ ip addr
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: enp0s31f6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000 link/ether c8:5b:ff:aa:bb:cc brd ff:ff:ff:ff:ff:ff inet 192.168.1.164/24 brd 192.168.1.255 scope global enp0s31f6 valid_lft forever preferred_lft forever inet6 fe80::6916:d619:b127:b0a7/64 scope link valid_lft forever preferred_lft forever
3: wlp1s0: <BROADCAST,MULTICAST> mtu 1500 qdisc mq state DOWN group default qlen 1000 link/ether e4:a4:ff:aa:bb:cc brd ff:ff:ff:ff:ff:ff
4: docker0: <BROADCAST,MULTICAST> mtu 1500 qdisc noqueue state DOWN group default link/ether 02:42:ff:4a:f3:d0 brd ff:ff:ff:ff:ff:ff
$ ip route
default via 192.168.1.1 dev enp0s31f6 proto static metric 100
169.254.0.0/16 dev enp0s31f6 scope link metric 1000
192.168.1.0/24 dev enp0s31f6 proto kernel scope link src 192.168.1.164 metric 100
Working Wifi Only:
$ ip addr
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: enp0s31f6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000 link/ether c8:5b:ff:aa:bb:cc brd ff:ff:ff:ff:ff:ff
3: wlp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000 link/ether e4:a4:ff:aa:bb:cc brd ff:ff:ff:ff:ff:ff inet 192.168.1.163/24 brd 192.168.1.255 scope global wlp1s0 valid_lft forever preferred_lft forever inet6 fe80::631:b92:a78:cc61/64 scope link valid_lft forever preferred_lft forever
4: docker0: <BROADCAST,MULTICAST> mtu 1500 qdisc noqueue state DOWN group default link/ether 02:42:ff:4a:f3:d0 brd ff:ff:ff:ff:ff:ff
$ ip route
default via 192.168.1.1 dev wlp1s0 proto static metric 600
169.254.0.0/16 dev wlp1s0 scope link metric 1000
192.168.1.0/24 dev wlp1s0 proto kernel scope link src 192.168.1.163 metric 600
Non-working Wifi and LAN
$ ip addr
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: enp0s31f6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000 link/ether c8:5b:ff:aa:bb:cc brd ff:ff:ff:ff:ff:ff inet 192.168.1.164/24 brd 192.168.1.255 scope global enp0s31f6 valid_lft forever preferred_lft forever inet6 fe80::6916:d619:b127:b0a7/64 scope link valid_lft forever preferred_lft forever
3: wlp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000 link/ether e4:a4:ff:aa:bb:cc brd ff:ff:ff:ff:ff:ff inet 192.168.1.163/24 brd 192.168.1.255 scope global wlp1s0 valid_lft forever preferred_lft forever inet6 fe80::631:b92:a78:cc61/64 scope link valid_lft forever preferred_lft forever
4: docker0: <BROADCAST,MULTICAST> mtu 1500 qdisc noqueue state DOWN group default link/ether 02:42:ff:4a:f3:d0 brd ff:ff:ff:ff:ff:ff
$ ip route
default via 192.168.1.1 dev enp0s31f6 proto static metric 100
default via 192.168.1.1 dev wlp1s0 proto static metric 600
169.254.0.0/16 dev enp0s31f6 scope link metric 1000
192.168.1.0/24 dev enp0s31f6 proto kernel scope link src 192.168.1.164 metric 100
192.168.1.0/24 dev wlp1s0 proto kernel scope link src 192.168.1.163 metric 6001 Answer
More than one interface on same sub-net, is not expected in network design.
Even you setup interface to have a working static routing, the other devices will not be aware of your device setup. So your device send packet on one interface, other devices don't care, their packets are not directed to specific interface but just IP. So coming packets are undefined on which interface to receive them.
More info check How to connect two network interfaces on the same subnet? yet not the canonical answer.
I am not the expert but experienced this multiple times. This is more generic than Duplicate IP on same network. It seems difficult to make every app, know about (two sets of IP/DEV) send on one and receive on both.
Some laptop manufacturer implement a feature in BIOS/UEFI firmware to switch automatically Wifi(WLAN)/MobileData(WWAN) interface OFF if detected a Wired interface is ON (direct cable or through Dock station).
At least, I use it on Dell Precision/Latitude. Settings in Dell: Wireless is disabled when Ethernet is connected
