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I have a Mac (OS X 10.5) that I would like to connect to a dedicated/isolated Internet connection (one that is not connected to the LAN), and a LAN.

The LAN is set up with its own, separate, Internet connection which is shared by several dozen computers (and is quite slow).

I want to set it up so that the Mac uses its own dedicated Internet connection (on a different account with a different company) for its Internet access, but can still access the local area network as well.

How can I configure the Mac & the network to allow this?

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Kyle, you might want to elaborate on the kind of connection you plan to use. wired LAN? wireless LAN? DSL? avian carriers? And you don't necessarily need 2 wired connections, either - for instance, my notebook has 1 wired ethernet, 1 modem, one 3G card, and 1 wireless network interface. Each of those can connect to the world :-) –  Florenz Kley Mar 25 '11 at 14:02
    
@Florenz Kley - the connection has to be wired for each, as neither is accessible via WiFi in the location I need to set this up (and installing WiFi for either network isn't an option right now). –  Kyle Lowry Mar 25 '11 at 14:53
    
ok, wires it will be. Much things can go over wires. Care to tell what kind of things? Like, ethernet? token ring? FDDI? eth-over-fc? PPP? If you want an answer, don't make it so hard guessing what you kind of connection you want :-) –  Florenz Kley Mar 25 '11 at 20:06

4 Answers 4

set the default route to the Internet, and add the (presumably private?) LAN as a "normal" route.

check with netstat and traceroute.

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You cannot connect to 2 access points / LAN's at once over the same physical interface.

What you can do is set up more than one virtual network interface over a single physical interface.

For example (on a terminal):

sudo ifconfig en1 inet 192.168.42.13 add

this will add a new connection (on the 42 subnet) on the en1 interface (normally en1 = wifi, en0 = wired).

So you should connect your DSL service to the same LAN (on a different subnet than the rest of the LAN users if necessary), and then set up the default connection to access your DSL, and a virtual connection to access the LAN.

But it requires some basic networking knowledge/tinkering plus probably some scripts to automate the whole thing.

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Each physical connection has separate settings:

enter image description here

You can just set up there, make up an IP in the network, add the router IP, and the subnet mask is almost certainly 255.255.255.0 (a network where only the last part changes, 254 clients, class c).

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I don't get it. Why make things up? I thought there was existing values? And I don't buy the a mask is "almost certainly" something specific. It's certainly anything. –  Florenz Kley Mar 22 '11 at 22:36
    
ah; I see. The issue I was having is that my Mac has only 1 physical interface for ethernet. So, presuming I can get my hands on a Mac with two ethernet jacks, I should be able to easily set this up. –  Kyle Lowry Mar 22 '11 at 23:15
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@Florenz It's a subnet mask, in normal class-based IPv4 there are only three possible things it could be en.wikipedia.org/wiki/Subnet_mask –  tobylane Mar 24 '11 at 23:04
    
@Kyle Either the second one isn't ethernet, or you have a mac pro I guess. –  tobylane Mar 24 '11 at 23:04
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Mac Pro's normally have two built-in gigabit ports; I suppose your's predates my concept of normally. PCI card should set you back less than $30 - may be worth the scratch to buy an intel rather than a $10 realek-based card, though one of those would be fine for the crappier net, I guess. My two networks are 255.255.192.0 and 255.255.252.0 netmasks (a /18 and a /22), for instance. –  Ecnerwal Oct 7 '13 at 2:37

I use virtual interfaces to make many interfaces on linux; I used this command:

ip link add link eth0 name eth0.100 type vlan id 10

You can add many virtual interfaces to make multiple networks.

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