in and outbound work well without Static Routes in my system, if that is the reason using Static Routes
debian-admin@vm-DEBIAN:~$ ip link show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
9: eth1: <BROADCAST,MULTICAST,DYNAMIC,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
link/ether 00:16:3e:55
debian-admin@vm-DEBIAN:~$ routel
Dst Gateway Prefsrc Protocol Scope Dev Table
default 10.10.8.1 eth1
10.10.8.0/24 10.10.8.3 kernel link eth1
10.10.8.1 link eth1
10.10.8.3 10.10.8.3 kernel host eth1 local
10.10.8.255 10.10.8.3 kernel link eth1 local
127.0.0.0/8 127.0.0.1 kernel host lo local
127.0.0.1 127.0.0.1 kernel host lo local
127.255.255.255 127.0.0.1 kernel link lo local
debian-admin@vm-DEBIAN:~$ traceroute google.com
traceroute to google.com (142.250.203.110), 30 hops max, 60 byte packets
1 10.10.8.1 (10.10.8.1) 0.349 ms 0.329 ms 0.275 ms
2 3.80.254.84.ftth.as8758.net (84.254.80.3) 1.884 ms 2.235 ms 2.564 ms
3 gwen.glb.as8758.net (212.25.27.124) 1.556 ms 1.894 ms grace.glb.as8758.net (212.25.27.126) 1.919 ms
4 212.25.28.50 (212.25.28.50) 0.925 ms 0.891 ms 0.821 ms
5 glyn.glb.as8758.net (212.25.27.247) 0.903 ms glyn.glb.as8758.net (212.25.27.245) 0.947 ms glyn.glb.as8758.net (212.25.27.247) 0.882 ms
6 83.150.38.119 (83.150.38.119) 1.121 ms 1.185 ms 72.14.198.50 (72.14.198.50) 1.214 ms
7 142.251.53.177 (142.251.53.177) 2.524 ms 142.251.245.151 (142.251.245.151) 1.099 ms 142.251.53.177 (142.251.53.177) 2.376 ms
8 192.178.254.76 (192.178.254.76) 1.524 ms 216.239.41.42 (216.239.41.42) 1.680 ms 142.251.70.185 (142.251.70.185) 0.930 ms
9 zrh04s16-in-f14.1e100.net (142.250.203.110) 1.484 ms 192.178.109.54 (192.178.109.54) 1.746 ms zrh04s16-in-f14.1e100.net (142.250.203.110) 0.811 ms
what leaves me still clueless is that I still can reach the VM via VNC and the TN host IP altough the don’t share a NIC.
RealVNC® Viewer 7.13.1 (r57) x64 (Dec 6 2024 18:17:18)
OS: Microsoft Windows 11, version 24H2, x64
Desktop name: QEMU (desktop-DEBIAN)
VNC Server: 10.10.9.231::5900 (TCP)
Size: 1280 x 800
Pixel format: depth 24 (32 bpp) little-endian rgb888
VNC Server default: depth 24 (32 bpp) little-endian rgb888
Audio format: VNC Server does not support audio
Requested encoding: ZRLE2
Last-used encoding: Hextile
Line-speed estimate: 100000 kbit/s (RTT ~0ms)
Protocol version: 3.8
Security method: no encryption [VncAuth]
Connection type: Direct TCP
Extensions: