Virtual network interface in Mac OS X

MacOS

Question or issue on macOS:

I know that you can make a virtual network interface in Windows (see here), and in Linux it is also pretty easy with ip-aliases, but does something similar exist for Mac OS X? I’ve been looking for loopback adapters, virtual interfaces and couldn’t find a good solution.

You can create a new interface in the networking panel, based on an existing interface, but it will not act as a real fully functional interface (if the original interface is inactive, then the derived one is also inactive).

This scenario is needed when working in a completely disconnected situation. Even then, it makes sense to have networking capabilities when running servers in a VMWare installation. Those virtual machines can be reached by their IP address, but not by their DNS name, even if I run a DNS server in one of those virtual machines. By configuring an interface to use the virtual DNS server, I thought I could test some DNS scenario’s. Unfortunately, no interface is resolving DNS names if none of them are inactive…

How to solve this problem?

Solution no. 1:

The loopback adapter is always up.

ifconfig lo0 alias 172.16.123.1 will add an alias IP 172.16.123.1 to the loopback adapter

ifconfig lo0 -alias 172.16.123.1 will remove it

Solution no. 2:

Replying in particular to:


You can create a new interface in the networking panel, based on an existing interface, but it will not act as a real fully functional interface (if the original interface is inactive, then the derived one is also inactive).

This can be achieved using a Tun/Tap device as suggested by psv141, and manipulating the /Library/Preferences/SystemConfiguration/preferences.plist file to add a NetworkService based on either a tun or tap interface. Mac OS X will not allow the creation of a NetworkService based on a virtual network interface, but one can directly manipulate the preferences.plist file to add the NetworkService by hand. Basically you would open the preferences.plist file in Xcode (or edit the XML directly, but Xcode is likely to be more fool-proof), and copy the configuration from an existing Ethernet interface. The place to create the new NetworkService is under “NetworkServices”, and if your Mac has an Ethernet device the NetworkService profile will also be under this property entry. The Ethernet entry can be copied pretty much verbatim, the only fields you would actually be changing are:

  • UUID
  • UserDefinedName
  • IPv4 configuration and set the interface to your tun or tap device (i.e. tun0 or tap0).
  • DNS server if needed.

Then you would also manipulate the particular Location you want this NetworkService for (remember Mac OS X can configure all network interfaces dependent on your “Location”). The default location UUID can be obtained in the root of the PropertyList as the key “CurrentSet”. After figuring out which location (or set) you want, expand the Set property, and add entries under Global/IPv4/ServiceOrder with the UUID of the new NetworkService. Also under the Set property you need to expand the Service property and add the UUID here as a dictionary with one String entry with key __LINK__ and value as the UUID (use the other interfaces as an example).

After you have modified your preferences.plist file, just reboot, and the NetworkService will be available under SystemPreferences->Network. Note that we have mimicked an Ethernet device so Mac OS X layer of networking will note that “a cable is unplugged” and will not let you activate the interface through the GUI. However, since the underlying device is a tun/tap device and it has an IP address, the interface will become active and the proper routing will be added at the BSD level.

As a reference this is used to do special routing magic.

In case you got this far and are having trouble, you have to create the tun/tap device by opening one of the devices under /dev/. You can use any program to do this, but I’m a fan of good-old-fashioned C myself:

#include 
#include 
#include 
int main()
{
   int fd = open("/dev/tun0", O_RDONLY);
   if (fd < 0)
   {
      printf("Failed to open tun/tap device. Are you root? Are the drivers installed?\n");
      return -1;
   }
   while (1)
   {
      sleep(100000);
   }
   return 0;
}

Solution no. 3:

In regards to @bmasterswizzle's BRILLIANT answer - more specifically - to @DanRamos' question about how to force the new interface's link-state to "up".. I use this script, of whose origin I cannot recall, but which works fabulously (in coordination with @bmasterswizzles "Mona Lisa" of answers)...

#!/bin/zsh

[[ "$UID" -ne "0" ]] && echo "You must be root. Goodbye..." && exit 1
echo "starting"
exec 4<>/dev/tap0
ifconfig tap0 10.10.10.1 10.10.10.255
ifconfig tap0 up
ping -c1 10.10.10.1
echo "ending"
export PS1="tap interface>"
dd of=/dev/null <&4 & # continuously reads from buffer and dumps to null

I am NOT quite sure I understand the alteration to the prompt at the end, or...


dd of=/dev/null <&4 & # continuously reads from buffer and dumps to null

but WHATEVER. it works. link light🚦: green✅. loves it💚.

enter image description here

Solution no. 4:

A few others seemed to hint at this, but the following demonstrates using ifconfig to create a vlan and test DNS on the virtual interface (using minidns) on OS X 10.9.5:

$ sw_vers -productVersion
10.9.5
$ sudo ifconfig vlan169 create && echo vlan169 created
vlan169 created
$ sudo ifconfig vlan169 inet 169.254.169.254 netmask 255.255.255.255 && echo vlan169 configured
vlan169 configured
$ sudo ./minidns.py 169.254.169.254 &
[1] 35125
$ miniDNS :: * 60 IN A 169.254.169.254


$ dig @169.254.169.254 +short test.host
Request: test.host. -> 169.254.169.254
Request: test.host. -> 169.254.169.254
169.254.169.254
$ sudo kill 35125
$ 
[1]+  Exit 143                sudo ./minidns.py 169.254.169.254
$ sudo ifconfig vlan169 destroy && echo vlan169 destroyed
vlan169 destroyed

Solution no. 5:

It's possible to use TUN/TAP device.
http://tuntaposx.sourceforge.net/

Solution no. 6:

What do you mean by


"but it will not act as a real fully functional interface (if the original interface is inactive, then the derived one is also inactive"

?

I can make a new interface, base it on an already existing one, then disable the existing one and the new one still works. Making a second interface does however not create a real interface (when you check with ifconfig), it will just assign a second IP to the already existing one (however, this one can be DHCP while the first one is hard coded for example).

So did I understand you right, that you want to create an interface, not bound to any real interface? How would this interface then be used? E.g. if you disconnect all WLAN and pull all network cables, where would this interface send traffic to, if you send traffic to it? Maybe your question is a bit unclear, it might help a lot if rephrase it, so it's clear what you are actually trying to do with this "virtual interface" once you have it.

As you mentioned "alias IP" in your question, this would mean an alias interface. But an alias interface is always bound to a real interface. The difference is in Linux such an interface really IS an interface (e.g. an alias interface for eth0 could be eth1), while on Mac, no real interface is created, instead a virtual interface is created, that can configured and used independently, but it is still the same interface physically and thus no new named interface is generated (you just have two interfaces, that are both in fact en0, but both can be enabled/disabled and configured independently).

Solution no. 7:

Take a look at this tutorial, it's for FreeBSD but also applies to OS X. http://people.freebsd.org/~arved/vlan/vlan_en.html

Solution no. 8:

if you are on a dev environment and want access some service already running on localhost/host machine. in docker for mac you have another option.use docker.for.mac.localhost instead of localhost in docker container.
docker.for.mac.host.internal should be used instead of docker.for.mac.localhost from Docker Community Edition 17.12.0-ce-mac46 2018-01-09.
this allows you to connect to service running on your on mac from within a docker container.please refer below links

understanding the docker.for.mac.localhost behavior

release notes

Solution no. 9:

i have resorted to running PFSense, a BSD based router/firewall to achieve this goal….

why? because OS X Server gets so FREAKY without a Static IP…

so after wrestling with it for DAYS to make NAT and DHCP and firewall and …

I'm trying this is parallels…

will let ya know how it goes...

Solution no. 10:

Go to Network Preferences.

At the bottom of the list of network adapters, click the + icons

Select the existing interface that you want to arp (say Ethernet 1), and give the Service Name that you want for the new port (say Ethernet 1.1) then press create.

Now you have the new virtual interface in the gui and can manage IP addresses etc it in the normal way.

ifconfig -a will confirm that you have multiple IPs on the interface, and these will still be there when you reboot.

Its a Mac. Don't fight it, do it the easy way.

Hope this helps!