When managing multiple internet lines on a MikroTik device, you don't necessarily have to avoid using NAT (Network Address Translation). In fact, NAT is essential for allowing multiple devices on your private network to access the Internet through one or more public IP addresses. The key is how you configure NAT and your routes to handle multiple internet connections.

For setups with multiple internet lines, you can use techniques like load balancing, failover, or even assign certain traffic to go out a specific connection based on rules, all of which may require NAT in different ways:

Load balancing

This involves distributing outbound traffic across your available internet lines to maximize the utilization of your network resources. In this scenario, you would use NAT along with mangrove rules in MikroTik to mark packets and then decide, based on these markings, over which internet line they should be routed. This ensures that outgoing traffic is correctly translated to the public IP addresses corresponding to each internet line.

Failover

In a failover configuration, NAT is still required to translate private addresses to a public IP address. The goal here is to provide redundancy; If an internet line fails, traffic is automatically redirected to another available line. The NAT configuration will work with routing rules and fault detection scripts to switch internet traffic to the backup connection.

Policy-based routes

You might want certain traffic to always go out over a specific Internet connection (for example, VoIP traffic over the most stable but not necessarily the fastest line). In this case, you would use NAT along with mangle and policy-based routing to ensure that traffic is correctly routed and translated to the appropriate public IP address.

In summary, rather than avoiding NAT, what you do in the presence of multiple lines to the Internet is configure NAT in a more complex and sophisticated way. The exact configuration will depend on your specific load balancing, failover, and traffic management needs.

MikroTik RouterOS is very flexible in this sense, offering multiple tools and options to manage complex network configurations.