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Quick question about routing

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Ok, I have a LAN with the following notes:

192.168.1.254 - Main router / default gateway for LAN
192.168.1.4   - Linux server (eth0)
192.168.1.8   - Windows laptop

Linux server (192.168.1.4) has ip(v4) forwarding enabled.

As an experiment I added an ip, 10.0.0.4, as eth0:0.

Then I added a static route for 10.0.0.0/8 using 192.168.1.4 as the 
gateway on the main router.

After that, I ran `ping 10.0.0.4` from the Windows laptop and the ping 
was successful.

While I do have plenty of networking experience and I'm not surprised 
that this worked, one thing sort of bugs me.

I'm able to ping an ip in the 10.0.0.0/8 subnet from a host that only 
has an ip in the 192.168.1.0/24 subnet. I know that the laptop is using 
the route from the default gateway (the main router) but how exactly is 
the ping getting back when the source of the ping isn't coming from 
another 10.0.0.0/8 address? Is this more due to ip forwarding, or 
because it's on the same physical network segment?

Again, I otherwise have a very good understanding of networking, but I 
can't seem to resolve this scenario completely in my mind, and would 
really like to know what exactly is happening here that allows the round 
trip to occur successfully.

-- 
szr

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Thread

Quick question about routing szr <szr@sREzMOrVEoman.com> - 2019-04-26 19:17 -0700
  Re: Quick question about routing William Unruh <unruh@invalid.ca> - 2019-04-27 03:02 +0000
  Re: Quick question about routing Pascal Hambourg <pascal@plouf.fr.eu.org> - 2019-04-27 09:14 +0200
    Re: Quick question about routing Theodore Heise <theise@panix.com> - 2019-04-27 14:28 +0000
    Re: Quick question about routing szr <szr@sREzMOrVEoman.com> - 2019-04-27 08:03 -0700

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