Is it possible to use AirDrop and Sidecar with a mac on a VPN

If you have a couple of computers kicking around to test AirDrop on, you can open a terminal on each machine and enter something like 'ifconfig -a' which will list all your networking interface cards. I'm not near a Mac or Unix box to show, but what you will see is a network interface that might be called say "en0" (Ethernet0) which is a physycal interface (may be wifi, or cabled) and a further one called "en0:0" which is a logical interface that piggybacks on top of the physycal interface. In this way you can run multiple virtual interfaces using just one physical one, and this is how AirDrop works. It is possible to manually create these interfaces yourself, and "multihome" your mac by having one interface say on a 192.168 address, and the other on say a 172.16 address, thus allowing it to talk to 2 networks at a time. It was always relatively straightforward on cabled interfaces, but I am not sure how tricky it would be (from a hardware support viewpoint) with wireless connections, but it's clearly possible in some way. See this question and answer for more details, but in short you need to be familiar with such terminal commands as ifconfig, netstat, route etc. Use the Airdrop network to access a computer?

I had the same problem on my Mac, and after fixing it I have figured out that it was caused by FortiClient (VPN client). Even when FortiClient was disconnected - it's DNS still appeared in the scutil.

The solution for me was:

scutil
> list ".*DNS"

This will show you a list of all DNS configs, that will look something like:

subKey [0] = State:/Network/Global/DNS <br>
subKey [1] = State:/Network/MulticastDNS<br>
subKey [2] = State:/Network/OpenVPN/DNS<br>
subKey [3] = State:/Network/OpenVPN/OldDNS<br>
subKey [4] = State:/Network/PrivateDNS<br>
subKey [5] = State:/Network/Service/forticlientsslvpn/DNS <br>

To check each of them run: (until you find the problematic one)

> get key_name
> d.show

…and to fix it run:

> get key_name
> d.remove ServerAddresses
> set key_name

This is how it looked on my machine:

> get State:/Network/Service/forticlientsslvpn/DNS 
> d.show
<dictionary> {
  ServerAddresses : <array> {
    0 : 192.168.30.6
    1 : 192.168.30.15
  }
  SupplementalMatchDomains : <array> {
    0 :
  }
  SupplementalMatchOrders : <array> {
    0 : 100000
  }
}
> d.remove ServerAddresses
> d.show
<dictionary> {
  SupplementalMatchDomains : <array> {
    0 :
  }
  SupplementalMatchOrders : <array> {
    0 : 100000
  }
}
> set State:/Network/Service/forticlientsslvpn/DNS
> exit