Internet through wireless hotspot, intranet through wired network - can I use both at the same time?

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I have been tring this for a while now, without success. I have read online this can be done, either by changing the default gateway (DG) or messing with the DG's metric

The short story is: I need to connect to my company's ERP system (port 80 for some web services and port 22 for sftp and bash) with using my notebook computer's LAN card - but I can't connect to the Internet on this network. So I have my mobile phone's 3g hotspot when I need to go online. But I want to use both at the same time without so much as opening another web browser process.

At the moment, I am using the ERP system regularly - and whenever I need to go online to check a mail or research something related to work, I need to unplug the network cable so the wifi can kick in... which is starting to become annoying especially if I am connected to the ERP system using FTP (Filezilla) or Shell (putty)

Can someone help me with the configurations?

Below are some of the details I can provide:

Wired network - office LAN - for connection to the ERP system:
DHCP -    Yes
IPv4      10.64.200.245
Subnet    255.255.240.0
DG        10.64.193.254
DHCP Serv 10.64.17.191
DNS       10.68.72.200
          10.68.20.200
WINS      10.68.77.200
          10.64.20.200

Below are the details for my WiFi internet connection - over my mobile hotspot

DHCP      Yes
IPv4      192.168.43.39 <- I'm guessing this changes every time I restart the wifi
subnet    255.255.255.0
DG        192.168.43.1
DHCP      192.168.43.1
DNS       192.168.43.1

Finally, here is the tracert results (btw, I'm on Windows 7, 64bit and the remote system should be on Linux) - the target ERP ip address is 10.76.142.39

Tracing route to 10.76.142.39 over a maximum of ...

  1    <1 ms    <1 ms    <1 ms  10.64.193.253
  2    <1 ms    <1 ms    <1 ms  10.64.4.13
  3    <1 ms    <1 ms    <1 ms  10.76.23.124
  4     1 ms    <1 ms    <1 ms  10.76.23.93
  5     1 ms    <1 ms    <1 ms  2xx-xx-xx-9.adsl...
  6     1 ms     1 ms     1 ms  2xx-xx-xx-9.adsl...
  7     1 ms     1 ms     1 ms  2xx-xx-xx-10.adsl..
  8     2 ms     1 ms     2 ms  10.76.135.125
  9     1 ms     1 ms     1 ms  10.76.142.39

sorry, I had to mask out some details above... wasn't sure if they would have any confidentiality issues.

Any help is much appreciated.

klee

Posted 2013-09-25T04:15:11.577

Reputation: 13

Answers

3

A default gateway means (simplistically) "If I don't have an explicit route for this network, send it to the default gateway".

It is the route that is taken by default. However, you can have specific routes for networks where you know how to get to them.

In your case, for any internet based destinations, which could be anything, you want to go via the hotspot, so your default gateway should be 192.168.43.1 on the wifi interface.

The wired interface should not have a default gateway at all. We know the destinations we want to access via this interface, so we can add specific routes. The next hop on that network is 10.64.193.254, so for any networks we want to get to internally, we can have a specific route to get to them.

By the look of it, they use the 10.x.x.x network for everything. So you can go to cmd and do:

route add 10.0.0.0 mask 255.0.0.0 10.64.193.254

And remove the default gateway from this interface.

So what we are saying is "If the destination network is in the 10.x.x.x range, send the traffic to 10.64.193.254 out of the wired interface, otherwise send it to 192.168.43.1 out of the wireless interface."

As 10.76.143.39 falls into the 10.0.0.0/255.0.0.0 network range, it will take the specific route added above.

Something like 8.8.8.8 does not fall into this range, and so will take the default route out of 192.168.43.1.

Paul

Posted 2013-09-25T04:15:11.577

Reputation: 52 173

wow, thanks for the quick reply. let me try this out and I'll get back to you. – klee – 2013-09-25T05:30:26.427

YES. it works. Thanks!.. though my first hop is actually to .253, so with that quick change, everything works now! Very much appreciated!! – klee – 2013-09-25T05:42:13.537

@klee Great news - but was the info wrong at the top in your ERP connection details (DG)? Or did it change? – Paul – 2013-09-25T06:07:11.367

yes, what i typed and what i traced was different... i typed "10.76.143.39" but it should be "10.76.142.39" -- as shown in the trace..

that wasn't the problem though... its the first hop in the trace, should be "10.64.193.253" and you typed "route add 10.0.0.0 mask 255.0.0.0 10.64.193.254" which caused a brain lapse for a second... but i quickly figured it out. – klee – 2013-09-25T06:39:25.590

1i'm just wondering though, at the moment, I let DHCP give me an IP, then go into network-settings for the LAN card and set the same settings, less the Default Gateway... which is kind of redundant and will probably stop working as soon as the DHCP ip lease is up... which is like 2 or 3 hours. Is there any way to let DHCP do its thing but still be able to clear the DG setting? – klee – 2013-09-25T06:44:10.147

@klee I am pretty sure DHCP will only request that it continue to use the same IP address as previously, rather than doing a full request, DNS and all. Did the settings get lost? – Paul – 2013-09-26T10:39:37.280

@klee by the way, the DG you have listed at the top of your question must be incorrect, so as it stands, the answer matches the question. If you update your question, I'll fix the answer. – Paul – 2013-09-26T10:41:35.590

I was only referring to your explanation after the 'route' command; when you say... "If the destination network is in the 10.x.x.x range, send the traffic to 10.64.193.254 out of the wired interface, otherwise send it to 192.168.43.1 out of the wireless interface."

but when i look at the route trace, i see that the first hop is to 10.64.193.253, so i'm wondering... should the tracert command point to 10.64.193.253 instead? – klee – 2013-09-29T06:27:10.367

okok... i see it... the DG for the Wired network is 10.64.193.254... so the route command should point to 10.64.193.254... is that the correct line of thought? – klee – 2013-09-29T06:29:02.470

@klee If that is the right router then yes. Note that a traceroute may not report the nearest interface, or even one that you can use for routing. – Paul – 2013-09-29T07:11:21.957

i have also figured it out; if I change the metric for the Wifi WAN interface to anything less than the default GW metric for the LAN interface, then I can simply leave all settings in my LAN-IP4 setup (automatic), and my internet packets will be routed through the Wifi WAN. Which means I don't even have to clear the Default GW setting on the LAN-IP4 setting – klee – 2013-10-03T08:18:41.290

Asked: 2013-09-25T04:15:11.577

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Active: 2013-09-25T06:50:14.743