To output a block of private IP addresses through a public IP address using BGP on a MikroTik router, you will need to configure NAT (Network Address Translation).

This is commonly required when you want multiple devices on a private network to access the Internet through a single public IP address.

We explain how you can configure this on your MikroTik router:

Step 1: Configure Public IP

Make sure your MikroTik router has a public IP address configured on the interface that is connected to your Internet provider. This address will be used to output your private blocks.

Step 2: Configure NAT

You will use the NAT functionality to translate the private IP addresses on your network to the public IP address configured on your router. Here I show you how to configure Network Address Translation (Source NAT) to allow private IP addresses to access the Internet:

/ip firewall nat
add chain=srcnat action=masquerade out-interface=ether1

In this example, ether1 should be replaced by the name of the interface where your public IP address is configured. The action masquerade is a form of Source NAT that automatically uses the IP address of the specified interface as the source address in outgoing packets.

Step 3: Verify BGP Routes

Make sure BGP routes are configured correctly so traffic can flow to and from your router. You do not need to advertise your private IP addresses over BGP, as they are generally not routable on the Internet.

Step 4: Firewall Rules

It is important to ensure that your firewall configuration allows outbound traffic from your private addresses and necessary inbound traffic. Here is an example of a firewall rule to allow all outgoing traffic:

/ip firewall filter
add chain=forward action=accept out-interface=ether1

Additionally, ensure that any security policies necessary to protect your internal network are properly implemented.

Step 5: Testing

After configuring NAT and firewall rules, perform tests to ensure that devices on your private network can access the Internet correctly and that traffic is being NATed as expected. You can do this by checking active connections in MikroTik:

/ip firewall connection print

This will show you the active connections and you should be able to see the address translations that occur thanks to NAT.

Conclusion

Configuring NAT on a MikroTik router to allow a block of private addresses to access the Internet through a public address while using BGP is a relatively straightforward process that involves making sure you have the proper NAT, firewall, and BGP settings.

These settings help ensure that your network is secure and traffic is handled correctly.