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How can I tell which network interface my computer is using?

How can I tell which network interface my computer is using?

On a MBP (OS X 10.6.2) I've got the wired ethernet and wireless airport configurations set up to use the same static IP to my router (e.g. as described at http://forums.macrumors.com/archive/index.php/t-708685.html). I've also got the Service Order set up so that the wired connection is above Airport (e.g. as described at Mac OS X automatically turn off Airport if ethernet cable is plugged in).

Asked by: Guest | Views: 336
Total answers/comments: 3
bert [Entry]

"Here's a dump of ifconfig -a in each situation (I'll highlight the differences afterward):

Ethernet cable is plugged in:

lo0: flags=8049 mtu 16384
inet6 ::1 prefixlen 128
inet6 xxxx::1%lo0 prefixlen 64 scopeid 0x1
inet 127.0.0.1 netmask 0xff000000
gif0: flags=8010 mtu 1280
stf0: flags=0 mtu 1280
en0: flags=8863 mtu 1500
inet6 xxxx%en0 prefixlen 64 scopeid 0x4
inet 192.168.0.110 netmask 0xffffff00 broadcast 192.168.0.255
ether xx:xx:xx:xx:xx:xx
media: autoselect (100baseTX ) status: active
supported media: none autoselect 10baseT/UTP 10baseT/UTP 10baseT/UTP 10baseT/UTP 100baseTX 100baseTX 100baseTX 100baseTX 1000baseT 1000baseT 1000baseT
fw0: flags=8863 mtu 4078
lladdr xx:xx:xx:xx:xx:xx
media: autoselect status: inactive
supported media: autoselect
en1: flags=8863 mtu 1500
inet6 xxxx%en1 prefixlen 64 scopeid 0x6
inet 192.168.0.110 netmask 0xffffff00 broadcast 192.168.0.255
ether xx:xx:xx:xx:xx:xx
media: autoselect status: active
supported media: autoselect

Ethernet cable is unplugged:

lo0: flags=8049 mtu 16384
inet6 ::1 prefixlen 128
inet6 xxxx::1%lo0 prefixlen 64 scopeid 0x1
inet 127.0.0.1 netmask 0xff000000
gif0: flags=8010 mtu 1280
stf0: flags=0 mtu 1280
en0: flags=8863 mtu 1500
ether xx:xx:xx:xx:xx:xx
media: autoselect status: inactive
supported media: none autoselect 10baseT/UTP 10baseT/UTP 10baseT/UTP 10baseT/UTP 100baseTX 100baseTX 100baseTX 100baseTX 1000baseT 1000baseT 1000baseT
fw0: flags=8863 mtu 4078
lladdr xx:xx:xx:xx:xx:xx
media: autoselect status: inactive
supported media: autoselect
en1: flags=8863 mtu 1500
inet6 xxxx%en1 prefixlen 64 scopeid 0x6
inet 192.168.0.110 netmask 0xffffff00 broadcast 192.168.0.255
ether xx:xx:xx:xx:xx:xx
media: autoselect status: active
supported media: autoselect

diff plugged unplugged shows that the wired connection does become active when it is available:

8,9d7
< inet6 xxxx%en0 prefixlen 64 scopeid 0x4
< inet 192.168.0.110 netmask 0xffffff00 broadcast 192.168.0.255
11c9
< media: autoselect (100baseTX <full-duplex,flow-control>) status: active
---
> media: autoselect status: inactive"
bert [Entry]

"Here's a dump of ifconfig -a in each situation (I'll highlight the differences afterward):

Ethernet cable is plugged in:

lo0: flags=8049 mtu 16384
inet6 ::1 prefixlen 128
inet6 xxxx::1%lo0 prefixlen 64 scopeid 0x1
inet 127.0.0.1 netmask 0xff000000
gif0: flags=8010 mtu 1280
stf0: flags=0 mtu 1280
en0: flags=8863 mtu 1500
inet6 xxxx%en0 prefixlen 64 scopeid 0x4
inet 192.168.0.110 netmask 0xffffff00 broadcast 192.168.0.255
ether xx:xx:xx:xx:xx:xx
media: autoselect (100baseTX ) status: active
supported media: none autoselect 10baseT/UTP 10baseT/UTP 10baseT/UTP 10baseT/UTP 100baseTX 100baseTX 100baseTX 100baseTX 1000baseT 1000baseT 1000baseT
fw0: flags=8863 mtu 4078
lladdr xx:xx:xx:xx:xx:xx
media: autoselect status: inactive
supported media: autoselect
en1: flags=8863 mtu 1500
inet6 xxxx%en1 prefixlen 64 scopeid 0x6
inet 192.168.0.110 netmask 0xffffff00 broadcast 192.168.0.255
ether xx:xx:xx:xx:xx:xx
media: autoselect status: active
supported media: autoselect

Ethernet cable is unplugged:

lo0: flags=8049 mtu 16384
inet6 ::1 prefixlen 128
inet6 xxxx::1%lo0 prefixlen 64 scopeid 0x1
inet 127.0.0.1 netmask 0xff000000
gif0: flags=8010 mtu 1280
stf0: flags=0 mtu 1280
en0: flags=8863 mtu 1500
ether xx:xx:xx:xx:xx:xx
media: autoselect status: inactive
supported media: none autoselect 10baseT/UTP 10baseT/UTP 10baseT/UTP 10baseT/UTP 100baseTX 100baseTX 100baseTX 100baseTX 1000baseT 1000baseT 1000baseT
fw0: flags=8863 mtu 4078
lladdr xx:xx:xx:xx:xx:xx
media: autoselect status: inactive
supported media: autoselect
en1: flags=8863 mtu 1500
inet6 xxxx%en1 prefixlen 64 scopeid 0x6
inet 192.168.0.110 netmask 0xffffff00 broadcast 192.168.0.255
ether xx:xx:xx:xx:xx:xx
media: autoselect status: active
supported media: autoselect

diff plugged unplugged shows that the wired connection does become active when it is available:

8,9d7
< inet6 xxxx%en0 prefixlen 64 scopeid 0x4
< inet 192.168.0.110 netmask 0xffffff00 broadcast 192.168.0.255
11c9
< media: autoselect (100baseTX <full-duplex,flow-control>) status: active
---
> media: autoselect status: inactive"
bert [Entry]

"I used the advice to make IP adresses the same for Ethernet and WiFi, Set the Service Order as suggested, and just used Network Utility>Info on en0 and en1.

I initiated a TimeMachine backup and under Network Utility > Info > en0 Ethernet I could see that thousands of packets were moving through the ethernet connection, while Network Utility > Info > en1 WiFi nothing was moving.

Thanks for getting me pointed in the right direction. When TimeMachine backup is complete I'll revert back to separate IP addresses and see if Mac automatically still moves everything through Ethernet.

The original question was ""How can I tell which network interface my computer is using?"" Network utility worked for me.

Macbook Pro 17"" Mid-2010, Mountain Lion"