Can't route specified site traffic to direct WiFi connection, to avoid VPN macOS Catalina 10.15.2

WiFi on en0 (MAC xx:xx:xx:xx:85:80)

VPN — Wireguard CLI (utun2)

I have a permanent VPN connection and all traffic is going through it. But I need to route traffic for music.yandex.ru (213.180.204.186) to the Wi-Fi connection.

I used the command route add -host music.yandex.ru -interface en0 to do it. The resulting routing table (netstat -nr) is below:

Destination        Gateway            Flags        Netif Expire
0/1                utun2              USc          utun2
default            192.168.43.63      UGSc           en0
10.217.47.164      10.217.47.164      UH           utun2
127                127.0.0.1          UCS            lo0
127.0.0.1          127.0.0.1          UH             lo0
128.0/1            utun2              USc          utun2
169.254            link#5             UCS            en0      !
190.2.141.162      192.168.43.63      UGHS           en0
192.168.43         link#5             UCS            en0      !
192.168.43.42/32   link#5             UCS            en0      !
192.168.43.63/32   link#5             UCS            en0      !
192.168.43.63      0:a:f5:12:f9:98    UHLWIir        en0   1197
213.180.204.186    xx:xx:xx:xx:85:80  UHLS           en0
224.0.0/4          link#5             UmCS           en0      !
224.0.0.251        1:0:5e:0:0:fb      UHmLWI         en0
255.255.255.255/32 link#5             UCS            en0      !


But after adding the route for music.yandex.ru it becomes unreacheable. I don't get any ping returns.

Then, I used direct forward to my gateway IP by route add -host music.yandex.ru 192.168.43.63

Internet:
Destination        Gateway            Flags        Netif Expire
0/1                utun2              USc          utun2
default            192.168.43.63      UGSc           en0
10.217.47.164      10.217.47.164      UH           utun2
127                127.0.0.1          UCS            lo0
127.0.0.1          127.0.0.1          UH             lo0
128.0/1            utun2              USc          utun2
169.254            link#5             UCS            en0      !
190.2.141.162      192.168.43.63      UGHS           en0
192.168.43         link#5             UCS            en0      !
192.168.43.42/32   link#5             UCS            en0      !
192.168.43.63/32   link#5             UCS            en0      !
192.168.43.63      0:a:f5:12:f9:98    UHLWIir        en0   1200
213.180.204.186    192.168.43.63      UGHS           en0
224.0.0/4          link#5             UmCS           en0      !
224.0.0.251        1:0:5e:0:0:fb      UHmLWI         en0
255.255.255.255/32 link#5             UCS            en0      !


And everything works as I want. But I need to use the network interface instead of the gateway IP, because it usually changes from time to time.

How can I set proper redirection?
Your usage of the -interface option is faulty. As the router's man page man routerdescribes: 


  If the destination is directly reachable via an interface requiring no
  intermediary system to act as a gateway, the -interface modifier should
  be specified; the gateway given is the address of this host on the common
  network, indicating the interface to be used for transmission.


The host music.yandex.ru (213.180.204.186) is no destination directly reachable via en0. It requires at least one intermediary system (your Wi-Fi router) to reach this host.

Compare this with your router:

192.168.43.63      0:a:f5:12:f9:98    UHLWIir        en0   1200


The router's Wi-Fi interface is "directly connected" to your Mac's Wi-Fi interface. 0:a:f5:12:f9:98 is your router's MAC-address (some Airgo/Qualcomm device).

Additional background: The MAC address is an address of a node on the data link layer (layer 2). Layer 2 has no routing capability. Routing is done on the network layer (layer 3) - nodes of the network layer have IP addresses!



If your VPN app doesn't provide the feature to route single IP-addresses to the system's default gateway (the IP address of your Wi-Fi router), you indeed have to create static routes.

To deal with changing networks (and thus changing default gateways) simply create different locations in System Preferences > Network > Location.