Post subject: Netmap vs dstnat & srcnat

I am about to replace an old Cisco SOHO Router with a MT RB1100 and want to make sure that I get it right. I have a /30 to the provider with a /28 routed over the /30. The Public IP's in the /28 are assigned (mapped) when needed to various private IP's in some /24 and /22 private subnets. All other IP's in the private /24 are natted to the Public /30. The Cisco didn't care which Public IP's went to which subnets or addresses as they were done with one rule for each mapping as below.

Natting a network range with NETMAP+Iptables

Some times we need to do a 1 to 1 NAT of a network range depending upon a condition (the destination network for example).
For example, you have the 192.168.1.0/24 network and you would like to NAT each IP to its equivalent in 192.168.2.0/24 when the packet travels through the NAT device.
If you use Netfilter as a NAT device or gateway you can use the NETMAP module like this :

iptables -t nat -A POSTROUTING -s 192.168.1.0/24 -d 10.1.1.0/24 -j NETMAP --to 192.168.2.0/24

In the example above, the source address 192.168.1.100 will become 192.168.2.100 while traversing the gateway.
I think that’s clear enough

NETMAP target

Linux Packet Filtering and iptables
Prev	Chapter 11. Iptables targets and jumps	Next

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11.11. NETMAP target

NETMAP is a new implementation of the SNAT and DNAT targets where the host part of the IP address isn't changed. It provides a 1:1 NAT function for whole networks which isn't available in the standard SNAT and DNAT functions. For example, lets say we have a network containing 254 hosts using private IP addresses (a /24 network), and we just got a new /24 network of public IP's. Instead of walking around and changing the IP of each and every one of the hosts, we would be able to simply use the NETMAP target like -j NETMAP -to 10.5.6.0/24 and voila, all the hosts are seen as 10.5.6.x when they leave the firewall. For example, 192.168.0.26 would become 10.5.6.26.