On Mon, 2025-03-03 at 17:21 +0100, Patrick Dupre via users wrote:
> Following your suggestion, I set the following
>
> On PC A, the interface for PC C with IP 10.42.1.1 with a gateway to 10.42.0.2
> and on PC C
> IP 10.42.1.2 with a gateway to 10.42.1.1
I am thoroughly confused by that description. The best I can guess is
that you've done this:
internet
192.168.43.1
|
|
192.168.43.115
PC B
10.42.0.1
|
|
10.42.0.5
PC A
10.42.1.1
|
|
10.42.1.2
PC C
> It let me communicate between PC A and PC C,
> But not between PC C and PC B.
> Would it be possible?
internet service
|
B
|
A
|
C
Each PC has its gateway address set to the IP of the device immediately above it
(the gateway is where non-local [not its own subnet] traffic goes through),
and each PC shares its internet out its interface facing downwards.
B has its gateway address set to the internet service IP (above) facing B,
B is sharing its internet out the downward facing interface,
B acts as the router between what's below it to the internet,
and routes any traffic that's not internal or LAN traffic out its gateway to the internet.
A has its gateway address set to B's IP facing A,
A is sharing its internet out the downward facing interface,
it will act as the router for C to B,
routing any traffic that's not meant to go downward, upward (in that diagram)
for itself and C.
C has its gateway address set to A's IP facing C,
all traffic that isn't internal will go through its gateway (A) upwards.
Draw a diagram for yourself, fill in the addresses, picture the routing
that has to be done. Make life easier for yourself, rather than
confusing random-seeming IPs, make the digits of your IPs logically
associated with your PC names.
A will have the hardest job of figuring out which direction to route
things upwards or downwards. I'm not sure if B could talk to C without
a fair bit of manual route configuration, too, C to B might be slightly
easier. Probably the best you could hope for is can each PC browse the
internet
In all seriousness, this is hard to manage correctly. And may not work
depending on how well its NAT has been programmed (by the programmer,
not just you). And may come to a grinding halt if the internet device
loses connectivity, reacquires it, and nothing below it knew about what
happened.
I'm not sure about this with Fedora, but with other systems I'd
certainly be getting one device at the top of the chain up and running,
then going down the chain one by one. I don't just mean doing the
configuration, I mean starting the network in a sequence. It is a
house of cards.
In the past I have tried doing what you are with a laptop, simply for
the sake of trying it, on an otherwise fully functional network. It
did not go well.
As you're double-NATing (or triple NATing, considering the mobile
internet device is also NATing), traffic will be fragile. And you will
have to manually reconfigure how A does its NAT for it to use
completely different IPs than what NAT is doing on B. This is more
than just manually configuring IPs for your interfaces, it's also
configuring IPs in NAT configuration.
You would be far better to swap a couple of computers around and have
just one gateway in the middle without all the daisy-chaining.
This kind of (family tree) NATing is painful enough:
internet
/ | \
router--router--router
/ | \ | \ / | \
PC PC PC PC PC PC PC PC
It's logical, and well within the abilities of NAT. Often, used to
deliberately isolate subnets from each other in large organisations,
with some very carefully configured interlinking for a few specific
things (such as mail servers). But that interlinking requires careful
consideration, and it's designed with minimal PC to PC communication
allowed.
I wouldn't attempt daisy chaining like you are doing.
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