On Sun, Sep 4, 2022 at 4:40 PM Rand Pritelrohm <rand.pritelr...@gmx.com>
wrote:
> Hello,
>
> I am not a network specialist and despite a lot of documentation
> readings and searchs on the net I haven't get a simple and clear answer
> to my question.
>
> Consider this simple schematic:
>
>
>     | VM | -----> | HOST | -----> | GW | -----> ISP
>
>
> Lets say the physical interface name on the 'host' is eth0 and the LAN
> subnet is 192.168.0.0.
>
> I want to configure the network on the 'host' in order for the VM to
> access the Internet.
>
> Thus I consider 2 scenarios to setup the 'host' network.
>
>
> 1. Bridge using routed subnet:
>
>     ip link add dev br0 type bridge
>     ip addr add 192.168.222.1/24 dev br0
>     ip link set dev br0 up
>
>     ip tuntap add tap0 mode tap
>     ip link set dev tap0 up
>     ip link set dev tap0 master br0
>
>     #Then I have to enable routing
>     echo '1' > /proc/sys/net/ipv4/ip_forward
>     iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
>
>
> 2. Bridge on the same subnet as the LAN:
>
>     ip link add dev br0 type bridge
>     ip link set dev br0 up
>
>     ip link set dev eth0 master br0
>     ip link set dev eth0 up
>     ip addr add 192.168.0.200/24 dev br0
>     ip route add default via 192.168.0.1
>
>     ip tuntap add tap0 mode tap
>     ip link set dev tap0 up
>     ip link set dev tap0 master br0
>
>
> For both scenarios the VM is then setup with it's own MAC address and
> it's IP on the configured subnet of the bridge.
>
>
> Here is my question:
>     For both scenarios, what is the effectively seen MAC address by the
>     GW when the VM access the Internet (host or VM MAC address)?
>
> Regards,
> Rand.
>
>
MAC is used in L2 networking level and GW is L3 routing hence the MAC is
irrelevant. If you run `ip route show` locally all you see is IPs and
network interfaces no MACs in there at all.

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