SDN not work properly

[redfury]

Hello guys, for a couple of days I am struggling to make it work SDN on a Proxmox instaled on a VPS but for no reason, it won't work. I work just once but because I added some iptables rules and mess it I reinstalled the Proxmox and since then, it never worked again.

1st The VPS have 4vCore 6GB of RAM and 600GB SSD.

IT came with Debian 12 installed and used official guide to install Proxmox. https://pve.proxmox.com/wiki/Install_Proxmox_VE_on_Debian_12_Bookworm

I added to /etc/network/interfaces the required line at the end: source /etc/network/interfaces.d/*

After that I used the official guide to configure SDN https://pve.proxmox.com/wiki/Setup_Simple_Zone_With_SNAT_and_DHCP

To test DHCP and internet functionality I build quickly an Ubuntu Container. And now here it comes. One time, but ONLY one time, the DHCP and internet was function correct. At that time I was struggling to find a way to forward some ports from a VM to be exposed to internet. But the DHCP and internet function correct (ping from CT/VM to google.com and response properly).

Since then I was trying several times to make the internet work but no luck. DHCP is working but not the internet. What in the hell is happening? Could be something related to VPS provider? What should I do/check in order to make it work again?

 

[redfury]

When I ping from CT/VM to GW (10.0.0.1) it responde, ping to VPS public IP response but ping to 8.8.8.8 no response. Also ping from Proxmox to CT no response.
This is the content of the sdn file:
#version:1

auto vnet0
iface vnet0
address 10.0.0.1/24
post-up iptables -t nat -A POSTROUTING -s '10.0.0.0/24' -o eth0 -j SNAT --to-source (my public IP)
post-down iptables -t nat -D POSTROUTING -s '10.0.0.0/24' -o eth0 -j SNAT --to-source (my public IP)
post-up iptables -t raw -I PREROUTING -i fwbr+ -j CT --zone 1
post-down iptables -t raw -D PREROUTING -i fwbr+ -j CT --zone 1
bridge_ports none
bridge_stp off
bridge_fd 0
ip-forward on

and the content of the interfaces file, I think configured by the VPS hoster via template or something.

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
address public ip/23
gateway 45.92.8.1
dns-search invalid
dns-nameservers 195.179.224.51 195.179.224.52
up ip route replace 45.92.8.0/23 via 45.92.8.1 dev eth0

iface eth0 inet6 static
address 2a02:c202:2205:4526:0000:0000:0000:0001/64
gateway fe80::1
accept_ra 0
autoconf 0
privext 0

source /etc/network/interfaces.d/*

2 questions:
1. can disable IPv6 as I do not need/use? Best method?
2. Can MTU be the cause of network malfunctioning as I see on this guide? at min 3:10 https://www.youtube.com/watch?v=UZ9mfxNMyHw&ab_channel=Jim'sGarage
I tried using 1460 but still not work.