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Routing tips for VPNs on OS X

When VPNs Just Work™, they're a fantastic way of allowing access to a private network from remote locations. When they don't work it can be an experience in frustration. I've had situations where I can connect to a VPN from my Mac, but various networking situations cause routing conflicts. Here are a couple of cases and how I've been able to get around them.

Specific cases

Case 1: conflicting additional routes.

In this example the VPN we are connecting to has a subnet that does not conflict with our local IP, but has additional routes that conflict in some way with our local network's routing. In my example the remote subnet is 10.0.x.0/24, my local subnet is 10.0.y.0/24, and the conflicting route is 10.0.0.0/8. Without the later route, I can't access all hosts on the VPN without manually adding the route after connecting to the VPN:

	#!/usr/bin/env bash

	# Originally published on https://magnushoff.com/blog/kick-the-bitbucket/

	# Copyright (c) 2019 Magnus Hovland Hoff
	#
	# Permission is hereby granted, free of charge, to any person obtaining a copy
	# of this software and associated documentation files (the "Software"), to deal
	# in the Software without restriction, including without limitation the rights
	# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

	using System.Threading.Tasks;
	using Newtonsoft.Json;
	using Refit;
	using System.Net.Http;
	using System;

	namespace wms_xamarin
	{
	public class LoginApi
	{

	// List available formats for ffmpeg
	ffmpeg -pix_fmts

	// Convert a 720x480 nv12 (yuv 420 semi-planar) image to png
	ffmpeg -s 720x480 -pix_fmt nv12 -i captdump-nv12.yuv -f image2 -pix_fmt rgb24 captdump.png

	// Convert a 640x480 uyvy422 image to png
	ffmpeg -s 640x480 -pix_fmt uyvy422 -i frame-000003.yuv -f image2 -pix_fmt rgb24 captdump.png

	// Display a 640x480 grayscale raw rgb file