Posts tagged nat

proxmox nat howto

posted on 2016-08-29 08:29

Network Adress Translation in combination with port forwarding lets you access a VM of a proxmox instance via the IP of the hypervisor itself. A second bridge is added for creating the internal network, and the hypervisor is configurated to forward packets destined to a certain port to the VM on the internal network. The added bridge is called vmbr1 here, and this was added to our networking config.

This is just an excerpt of the relevant part of the /etc/network/interfaces file there:

auto vmbr1
iface vmbr1 inet static
    address  10.0.2.1
    netmask  255.255.255.252
    bridge_ports none
    bridge_stp off
    bridge_fd 0

    post-up echo 1 > /proc/sys/net/ipv4/ip_forward
    post-up iptables -t nat -A POSTROUTING -s 10.0.2.0/30 -o eth0 -j MASQUERADE
    post-up iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 2222 -j DNAT --to 10.0.2.2:22

    post-down iptables -t nat -D POSTROUTING -s 10.0.2.0/30 -o eth0 -j MASQUERADE
    post-down iptables -t nat -D PREROUTING -i eth0 -p tcp --dport 2222 -j DNAT --to 10.0.2.2:22 

This is the network configuration for the VM in question:

auto eth0
iface eth0 inet static
    address 10.0.2.2
    netmask 255.255.255.252
    gateway 10.0.2.1

As soon as the bridge on the HV is started, the masqerading and port forwarding rules are added, they are removed again when the interface gets disabled.

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