С OpenVPN это сделать сравнительно легко — у него имеется встроенное средство переназначения сетей.
--client-nat args
This pushable client option sets up a stateless one-to-one NAT rule on packet addresses (not ports), and is useful in cases where routes or ifconfig settings pushed to the client would
create an IP numbering conflict.
Examples:
client-nat snat 192.168.0.0/255.255.0.0
client-nat dnat 10.64.0.0/255.255.0.0
network/netmask (for example 192.168.0.0/255.255.0.0) defines the local view of a resource from the client perspective, while alias/netmask (for example 10.64.0.0/255.255.0.0) defines
the remote view from the server perspective.
Use snat (source NAT) for resources owned by the client and dnat (destination NAT) for remote resources.
Set --verb 6 for debugging info showing the transformation of src/dest addresses in packets.
А с другими типами — использовать ядерное переназначение через iptables/nftables: DNAT/SNAT, NETMAP.
