Why 198.18.0.0/15 ?

[r3a1d3a1]

In routing config for Mac, it's suggested to add a route for 198.18.0.0/15 though the range is already contained in 128.0.0.0/1. Is there a rationale behind it?

[r3a1d3a1]

@xjasonlyu Also, the only difference between

sudo route add -net 1.0.0.0/8 198.18.0.1
sudo route add -net 2.0.0.0/7 198.18.0.1
sudo route add -net 4.0.0.0/6 198.18.0.1
sudo route add -net 8.0.0.0/5 198.18.0.1
sudo route add -net 16.0.0.0/4 198.18.0.1
sudo route add -net 32.0.0.0/3 198.18.0.1
sudo route add -net 64.0.0.0/2 198.18.0.1
sudo route add -net 128.0.0.0/1 198.18.0.1

and simply 0.0.0.0/0 is the 0.0.0.0/8 block. So why is 0.0.0.0/8 left out?!

[xjasonlyu]

This routing configuration is just a common suggestion that fits the majority of usage scenarios.

0.0.0.0/8 is not used for Internet routing, so it can be ignored. https://en.wikipedia.org/wiki/Reserved_IP_addresses

198.18.0.0/15 is a reversed IP range that was commonly used in tun2socks, but it's not the only IP range. In fact, you can choose any reversed IP range you like.

[r3a1d3a1]

Thanks for the reply. My question was that why not simply use 0.0.0.0/0 i.e. default instead of all those rules? like so:

route delete default;
route add default 198.18.0.1

(The only difference is the 0.0.0.0/8 block which -as you mentioned- does not seem to matter anyway.)

[xjasonlyu]

It's a good question. If you change the default gateway, you will have to change it back when you close the tun2socks, otherwise you will lose the connection. But using multiple such routes won't affect the default route and you can exit tun2socks anytime without worrying about the connection loss.

[xjasonlyu]

In short, it won't mess up the original default gateway/route.

[r3a1d3a1]

Great, thanks for confirming! I thought maybe there's more to it than what I know.