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Comment by sargun | Hacker News Reader

It turns out this is kind of already in the Linux Kernel. See here: https://lwn.net/Articles/614348/

You can tunnel TCP / IP / GRE, reasonably even Ethernet itself over UDP. This is actually really interesting for cases where you want layer 2 bridging over the internet without all the complexity and overhead of a VPN.

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Wouldn't work directly here, as "ip fou add" reserves a local port, while in OP's case it's a reserved remote port. And reserving local port 53 in case of 53<->53 packets would kill dns resolution.

With an extra iptables rule should work though:

  iptables -t nat -A PREROUTING -s my.server -p udp --sport 53 -d DNAT --to 127.0.0.1:5555
  ip fou add port 5555 ipproto 4

Agreed. The same is true for VXLAN which is also in the Kernel and also runs over UDP.

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