Thank for the feedback.

Yes the schamatics is correct.

I set the gateway and now it works.

Now

1) I wish to use internet from PC A.

I guess that I need to set a name server

But not possible manually

2) How do I need to set for PC 3

From PC A

From PC C

I tried several things but none works

On Sat, 1 Mar 2025 at 22:22, Patrick Dupre via users <users@lists.fedoraproject.org> wrote:

I am lost.

I had a configuration with was working, but my usb WiFi doogle does not work anymore.
The configuration which was working

Doogle on PC A with 2 ethernet cards.
One connected to PC B: a laptop
one connected to PC C

Now, The laptop PC B is connect to a wifi mobile.
It works
wlp2s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.43.115 netmask 255.255.255.0 broadcast 192.168.43.255

I set the ethernet interface "shared to other computers"
enp3s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 10.42.0.1 netmask 255.255.255.0 broadcast 10.42.0.255

Now I am trying to connect this ethernet card to PC A
From the network interface, It tried
"shared to other computers"
and
"Automatic (DHCP)",
but none of them allow me to make the connection
(connecting for ever).
Hence, I tried manually
10.42.0.5 255.255.255.0
It connected
enp1s0 flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 10.42.0.5 netmask 255.255.255.0 broadcast 10.42.0.255

But the 2 computers do not talk together
From PC B to PC A:
ping 10.42.0.5
PING 10.42.0.5 (10.42.0.5) 56(84) bytes of data.
From 10.42.0.1 icmp_seq=1 Destination Host Unreachable
traceroute to 10.42.0.5 (10.42.0.5), 30 hops max, 60 byte packets
1 Sappho (10.42.0.1) 3068.823 ms !H 3068.691 ms !H 3068.614 ms !H
route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.43.1 0.0.0.0 UG 600 0 0 wlp2s0
10.42.0.0 0.0.0.0 255.255.255.0 U 100 0 0 enp3s0
192.168.43.0 0.0.0.0 255.255.255.0 U 600 0 0 wlp2s0

From PC A to PC B:
same behavior
route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
10.42.0.0 0.0.0.0 255.255.255.0 U 100 0 0 enpls0
192.168.122.0 0.0.0.0 255.255.255.0 U 600 0 0 virbr0

I think if I'm reading your description correctly, this is roughly your topology and addressing?

https://photos.app.goo.gl/sWCqtQNNBBzBuGWk9

If my understanding is correct

- the default gateway (0.0.0.0) from PC A (10.42.0.5) needs to be PC B (10.42.0.1)

- you probably don't want 192.168.0.122.0 to be a gateway configured on PC A

- you probably need ip_forwarding (net.ipv4.ip_forward) enabled on PC B if it's being used as an ersatz router