Make default gateway IP '.1' instead of '.254'

[emtuls]

Having the default gateway be set to the common default IP address of the Virtual Adapter (.1) fixes an issue where FakeNet expects to be able to reach out of the guest via the DHCP server which it assumes is at .254.

The DHCP server is only at .254 if using VMware and the last address in the IP pool for DHCP is .254, which is fairly common, but this is not the case on VirtualBox. VirtualBox uses 1 IP address less than the lowest address in the IP pool for DHCP and thus, FakeNet does not work out of the box for VirtualBox.

If we instead use the IP Address of the Virtual Adapter created by VMware and VirtualBox, which is typically the .1 address, we can make FakeNet work out of the box for both of these platforms.

Context wise, this is for a Host-Only network for a guest VM where DHCP is enabled.

[stevemk14ebr]

LGTM! Tested this with Elliot last week, great work identifying the fix!

[thejoelpatrol]

It has been a while since I have tried it, but last time I used VirtualBox, .1 did not work for the gateway with the current version of FakeNet at that time.

I filed an issue about it but then went back to using VMWare: #168
If this is resolved since then, we can close that.

[emtuls]

@thejoelpatrol That is interesting...
I have never hit the issue of FakeNet not being able to set the Gateway like that. And for the .100 case, I suspect that is the DHCP server address that your adapter is being set to use, if you were to check in the VirtualBox Network Settings.
.1 seems to work for myself and @stevemk14ebr when we tested.

In all of my testing, FakeNet always sets the Gateway to .254 which FakeNet uses as a default and can be seen here:

flare-fakenet-ng/fakenet/diverters/winutil.py

Line 366 in ac33a70

gw_address = ip_address[:ip_address.rfind('.')] + '.254'

And that of course fails in VirtualBox due to it not being the DHCP server (at least not by default) or the Virtual Adapter address (which is typically .1).

Here is that default on version 1.4.11 (most of my testing was on version 3.0-alpha) where it tries .254 and everything fails:

And here is the change to .1 with the pings working (along with testing things like google.com):

Also, here it is with the change to .1, but instead of setting manually through the GUI, I tried with the same command you used to see if that made a difference:

I am on VirtualBox 7.0.14r161095, Virtualbox Guest Additions: 7.0.14

[thejoelpatrol]

@emtuls thanks for all that testing. I can't explain why it didn't work for me at that time, I didn't dig into the FakeNet code to try to understand it fully beyond just figuring out how to reproduce it locally. I hope it was something specific to my setup that was uncommon. But just something to be aware of, in case it's one of those bugs that goes away by itself and then comes back by itself.

[tinajohnson]

Thanks for the PR, @emtuls! Tested from my end as well and the fix works smoothly.

[strictlymike]

Approved for pre-release