Mac OSX: Altering the OS route table to re-direct the traffic of a website to a different interface (eg re-routing whatsapp traffic to en0)

This was a hard article to figure out the title for! Put simply, your mac book has a route table and if you want to move a specific IP address or dns from one interface to another, then follow the steps below:

First find the IP address of the website that you want to re-route the traffic for:

$ nslookup web.whatsapp.com
Server:		100.64.0.1
Address:	100.64.0.1#53

Non-authoritative answer:
web.whatsapp.com	canonical name = mmx-ds.cdn.whatsapp.net.
Name:	mmx-ds.cdn.whatsapp.net
Address: 102.132.99.60

We want to re-route traffic the traffic from: 102.132.99.60 to the default interface. So first lets find out which interface this traffic is currently being routed to?

$ route -n get web.whatsapp.com
   route to: 102.132.99.60
destination: 102.132.99.60
    gateway: 100.64.0.1
  interface: utun0
      flags: <UP,GATEWAY,HOST,DONE,WASCLONED,IFSCOPE,IFREF>
 recvpipe  sendpipe  ssthresh  rtt,msec    rttvar  hopcount      mtu     expire
       0         0         0        34        21         0      1400         0

So this is currently going to a tunnelled interface called utun0 on gateway 100.64.0.1.

Ok, so I want to move if off this tunnelled interface. So lets first display the kernel routing table. The -n option forces netstat to print the IP addresses. Without this option, netstat attempts to display the host names.

$ netstat - rn | head -n 5
Active Internet connections
Proto Recv-Q Send-Q  Local Address          Foreign Address        (state)
tcp4       0    126  100.64.0.1.64770       136.226.216.14.https   ESTABLISHED
tcp4       0      0  100.64.0.1.64768       whatsapp-cdn-shv.https ESTABLISHED
tcp4       0      0  100.64.0.1.64766       52.178.17.3.https      ESTABLISHED

Now we want to re-route whatsapp to the default interface. So lets get the IP address of the default interface.

$ netstat -nr | grep default
default            192.168.8.1        UGScg                 en0
default                                 fe80::%utun1                            UGcIg               utun1
default                                 fe80::%utun2                            UGcIg               utun2
default                                 fe80::%utun3                            UGcIg               utun3
default                                 fe80::%utun4                            UGcIg               utun4
default                                 fe80::%utun5                            UGcIg               utun5
default                                 fe80::%utun0                            UGcIg               utun0

We can see that our en0 interface is on IP address: 192.168.8.1. So lets re-route the traffic from Whatsapp’s ip address to this interace’s IP address:

$ sudo route add 102.132.99.60 192.168.0.1
route: writing to routing socket: File exists
add host 102.132.99.60: gateway 192.168.8.1: File exists

Now lets test if we are routing via the correct interface:

$ route -n get 102.132.99.60
   route to: 102.132.99.60
destination: 102.132.99.60
    gateway: 192.168.8.1
  interface: utun6
      flags: <UP,GATEWAY,HOST,DONE,STATIC>
 recvpipe  sendpipe  ssthresh  rtt,msec    rttvar  hopcount      mtu     expire
       0         0         0         0         0         0      1400         0

Finally delete the route and recheck the routing:

$ sudo route delete 102.132.99.60
delete host 102.132.99.60

$ route -n get 102.132.99.60
   route to: 102.132.99.60
destination: 102.132.99.60
    gateway: 100.64.0.1
  interface: utun6
      flags: <UP,GATEWAY,HOST,DONE,WASCLONED,IFSCOPE,IFREF>
 recvpipe  sendpipe  ssthresh  rtt,msec    rttvar  hopcount      mtu     expire
       0         0         0         0         0         0      1400         0