Possible to config an application to use LAN or Wi-Fi access?

Question

MacBook Air networking setup is:

• Internet connection via WiFi via proxy: en0
• LAN connection via ethernet: en6

For example:

en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
ether 00:1f:f3:ba:82:57 
inet6 fe80::21f:f3ff:feba:8257%en0 prefixlen 64 scopeid 0x4 
inet 192.168.182.136 netmask 0xffffff00 broadcast 192.168.182.255
media: <unknown subtype>
status: active

en6: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
ether 00:1f:f3:8c:3d:92 
inet6 fe80::21f:f3ff:fe8c:3d92%en6 prefixlen 64 scopeid 0x5 
inet 192.168.8.251 netmask 0xffffff00 broadcast 192.168.8.255
media: autoselect (100baseTX <full-duplex,flow-control>)
status: active

When I open a Terminal or a browser, I can access either the internet (e.g. Google.com), when WiFi is on. Or I can access the local network (e.g. 192.168.x.x) when the WiFi is off. But not both (probably due to both connections are on 192.168.x.x).

Is it possible to config one app to use a particular connection (e.g. Terminal uses en6, FireFox uses en0)?

UPDATE (information regarding Spiff's answer):

1. In network preferences, AirPort is on top of USB Ethernet

2. When Wi-Fi is up:

   Routing tables
   
   Internet:
   Destination        Gateway            Flags        Refs      Use   Netif Expire
   
   default            192.168.182.1      UGSc           26        0     en0
   default            192.168.8.10       UGScI           2        0     en6
   17.82.253.7        192.168.182.1      UGHWI           1        1     en0
   64.34.80.176       192.168.182.1      UGHWI           1       11     en0
   69.59.196.211      192.168.182.1      UGHWI           1       35     en0
   69.59.196.216      192.168.182.1      UGHWI           1        6     en0
   72.21.91.19        192.168.182.1      UGHW3I          0        2     en0   3295
   72.233.61.123      192.168.182.1      UGHWI           2       10     en0
   74.125.71.18       192.168.182.1      UGHWI           1       90     en0
   74.125.71.19       192.168.182.1      UGHW3I          0        1     en0   3418
   74.125.71.83       192.168.182.1      UGHWI           1       25     en0
   74.125.71.100      192.168.182.1      UGHW3I          0       36     en0   3433
   74.125.71.101      192.168.182.1      UGHW3I          0        6     en0   3433
   74.125.71.104      192.168.182.1      UGHW3I          0        9     en0   3432
   74.125.71.105      192.168.182.1      UGHW3I          0       27     en0   3433
   74.125.71.106      192.168.182.1      UGHWI           1       16     en0
   74.125.71.113      192.168.182.1      UGHWI           1        5     en0
   74.125.71.138      192.168.182.1      UGHWI           1        6     en0
   74.125.71.139      192.168.182.1      UGHWI           1        9     en0
   74.125.71.189      192.168.182.1      UGHW3I          0       12     en0   3432
   74.201.86.29       192.168.182.1      UGHWI           1       93     en0
   127                127.0.0.1          UCS             0        0     lo0
   127.0.0.1          127.0.0.1          UH              4     6062     lo0
   169.254            link#4             UCS             0        0     en0
   174.36.30.38       192.168.182.1      UGHWI           1       19     en0
   192.168.8          link#5             UCS             8        0     en6
   192.168.8.10       0:12:a9:c5:41:0    UHLWI           1        0     en6   1198
   192.168.8.11       0:24:73:7c:87:41   UHLWI           0        0     en6   1187
   192.168.8.251      127.0.0.1          UHS             0        0     lo0
   192.168.8.255      ff:ff:ff:ff:ff:ff  UHLWbI          0        1     en6
   192.168.12.21      192.168.8.10       UGHW3I          0       19     en6   3281
   192.168.13.183     192.168.8.10       UGHWI           1       23     en6
   192.168.65         link#7             UC              3        0  vmnet1
   192.168.65.255     ff:ff:ff:ff:ff:ff  UHLWbI          0        1  vmnet1
   192.168.182        link#4             UCS             4        0     en0
   192.168.182.1      0:c0:df:3:f0:db    UHLWI          15       59     en0   1166
   192.168.182.150    127.0.0.1          UHS             0      108     lo0
   192.168.182.255    ff:ff:ff:ff:ff:ff  UHLWbI          0        1     en0
   192.168.214        link#8             UC              4        0  vmnet8
   192.168.214.1      0:50:56:c0:0:8     UHLWI           0      212     lo0
   192.168.214.255    ff:ff:ff:ff:ff:ff  UHLWbI          1        1  vmnet8
   192.221.72.126     192.168.182.1      UGHW3I          0        4     en0   3478
   192.221.73.126     192.168.182.1      UGHWI           1       19     en0
   203.190.124.12     192.168.182.1      UGHW3I          0        7     en0   3573
   207.171.166.37     192.168.182.1      UGHWI           1        5     en0
   224.0.0.251        192.168.182.1      UGHmWI          1        0     en0
   255.255.255.255    192.168.182.1      UGHW3bI         0       11     en0   3575
   

   When Wi-Fi is off:

   Routing tables
   
   Internet:
   Destination        Gateway            Flags        Refs      Use   Netif Expire
   default            192.168.8.10       UGSc            2        0     en6
   17.82.253.7        192.168.8.10       UGHW3I          0        0     en6   3599
   127                127.0.0.1          UCS             0        0     lo0
   127.0.0.1          127.0.0.1          UH              4     6032     lo0
   169.254            link#5             UCS             0        0     en6
   192.168.8          link#5             UCS             5        0     en6
   192.168.8.10       0:12:a9:c5:41:0    UHLWI           3        0     en6   1198
   192.168.8.11       0:24:73:7c:87:41   UHLWI           0        0     en6   1199
   192.168.8.106      0:9:6b:55:c6:1e    UHLWI           1       36     en6   1200
   192.168.8.251      127.0.0.1          UHS             0        0     lo0
   192.168.12.21      192.168.8.10       UGHWI          20       36     en6
   192.168.65         link#7             UC              2        0  vmnet1
   192.168.214        link#8             UC              4        0  vmnet8
   192.168.214.1      0:50:56:c0:0:8     UHLWI           0      212     lo0
   

3. Yes, I want to access: 192.168.13.*, 192.168.12.*, for example.

4. It's a MacBook Air. en6 may be caused by a) it's USB Lan b) installed after some VMWare virtual lan cards.

5. No. All traffic via LAN cannot connect internet.

6. Not sure what is a "multi-hop". Basically, 1) the LAN goes into company intranet, in which I want to access the 192.168.13.* and 192.168.12.*. However, when WiFi is on, it seems there is no route to 192.168.13.* and 192.168.12.* (probably they go to the WiFi-size of 192.168.13.* and 192.168.12.*). 2) The WiFi goes into the company WiFi which has a proxy to connect to the internet.

7. I think there are on the Wi-Fi side, not the (real) hosts I am trying to connect.

8. Before I try that, could you please teach me how to revert (delete) them.

And no, after the 2 route adds, still cannot connect to a 192.168.12.? host.

Answer 1

I don't think you need to lock apps to interfaces to fix your problem. I think you've got a simple networking configuration error.

Mac OS X automatically talks to local subnets via any active interface, and non-local subnets via the default route, which is automatically set to be the highest-ranked active interface.

In this context, "active" means that link is up. On Ethernet, that would mean a link light on the switch. On 802.11, that would mean that you're associated to an AP.

In the ifconfig output in your Question, you should be able to access the 192.168.182/24 subnet via en0 (which appears to be WiFi), and you should be able to access the 192.168.8/24 subnet via en6 (Ethernet). All other subnets will be reached via whichever active interface is highest-ranked in "System Preferences > Network > ["Gear icon" menu] > Set Service Order..."

The fact that both of your local subnets start with 192.168 doesn't matter; your subnet mask in both cases is /24, so the third octet matters, and the third octet is different between en0 and en6, so these are different subnets.

It sounds like this isn't working right on your system, which leads me to the following questions:

1. How do you have things ranked in "Set Service Order"? NOTE: This can be DIFFERENT than how they appear in the summary view on the main panel of the Network pref pane.

2. What does netstat -rnaf inet show when WiFi is up? What does it show when Wi-Fi is down?

3. Does the "local network" that you want to get to over Ethernet consist of more than one subnet? [If so, then everything might be working as designed, but you need to add static routes to the non-local subnets on your LAN, or have your LAN advertise those routes to your host via RIP or something]

4. Usually on a MacBook, the built-in Ethernet is en0, and the built-in Wi-Fi card is en1. If this is a MacBook and not a MacBook Air, it's weird that the AirPort card (assuming when you say "Wi-Fi" you mean the built-in AirPort card and not some third-party external USB Wi-Fi dongle or something like that) is at en0 instead of en1. It's also weird that Ethernet (even if it's a dongle, but especially if it's built-in Ethernet) is at en6. This strikes me as either a network config that's been migrated from one machine to another to another a few times, or a system that's seen lots of different USB networking dongles installed and removed, or a system that has had a lot of other network configuration changes done to it.

   That is to say, I wonder if your network configuration files have developed errors over time and need to be cleaned up. It might be worthwhile to delete all your network settings (all the .plist files in /Library/Preferences/SystemConfiguration/), and start over, configuring networking from scratch.

Update: More questions after your update:

5. So, the LAN out your Ethernet port...does that LAN have Internet access or not? It looks like it might, since it looks like you established a route to time.asia.apple.com (Apple's NTP server for Asia) via that interface.

6. Why do you have a multi-hop Ethernet LAN? How does your Wi-Fi network relate to that LAN? Can you explain or diagram your network topology? If this network is under your control, it's possible you can work around this with a minor network redesign.

7. It looks like you've got routes to 192.168.12.21 and 192.168.13.183 via Ethernet even when Wi-Fi is up. Are those hosts actually reachable in that situation?

8. Bring Wi-Fi up and then try these commands to add routes to the .12 and .13 networks, to see if it temporarily resolves your problem:

   sudo route add -net 192.168.12/24 192.168.8.10
   sudo route add -net 192.168.13/24 192.168.8.10