Newbe Dev Stack

Answer : Hetzner had stopped assigning public IPv4 addresses to virtual servers. As far as I can tell this change happened when they changed the product name from VQ to CX. The usage of NAT is not mentioned in the product description though. Eventually Hetzner introduced a newer cloud platform in which VMs get real public IPv4 addresses and a routed /64 IPv6 prefix. Both versions share the CX name. Virtual servers ordered in 2012 and 2013 would keep their public IPv4 address until 2019 when the VQ line was discontinued. But virtual servers ordered in 2016 only have an RFC1918 address, and Hetzner will not route a public IPv4 address to such a virtual server. They still allocated a dedicated public IPv4 address to each virtual server, which they NAT to the assigned RFC1918 address. Hetzner believed this was not a problem because it was a 1:1 NAT. As you found out, this is error prone when configuring the server. You have to know about this NAT. And you have to look up the map...

Answer : The easiest way to configure this would be to use a Multi-WAN router such as the Linksys RV042. Technically: yes In practice, it's an exotic and expensive configuration. You can put more than one address on an interface or use more than one interface and be multihomed . However, this is much more likely to be effective for a big server cluster in a data center. Expensive routers capable of running routing protocols will be needed and then it still would not help you with a single given TCP connection. If you try this as a single user of two retail ISPs, then you will have two different IP addresses, so incoming traffic will use the one you made the outbound connection on, and it's unlikely that any equipment you have can be configured with more than one gateway. A large site with a /24 or shorter prefix and their own ASN can actually announce a single IP address over multiple networks, but that won't work without being further upstream than a retail...