![]() with IPs ranging from 10.0.100.0 to 10.0.103.255) for which our firewall has a known route. On the right there is a partner’s network, 10.0.100.0/22 (i.e. ![]() Fortinet instead has a different order of operations, more like Linux with Iptables: the packet arrives from the incoming interface, there is a pre-routing step where Destination NAT (DNAT from now on) happens, follows a routing decision (since now the final destination is known) that determines the outgoing interface, security policies (IPv4 policies) are examined and finally Source NAT (SNAT from now on) takes place and the packet can be sent out on the outgoing interface (more detail can be found here, I’ve omitted a lot of other intermediate steps).ĭuring the rules’ migration, I’ve had the necessity to implement SNAT and DNAT rules to map a /22 network onto another /22 network, with deterministic mappings. ![]() Checkpoint applies security policies first (at least the version I’m using) and then it checks the NAT policies and applies both source and destination NAT. I’ve recently had to migrate some firewall security and NAT rules from Checkpoint to Fortinet firewalls and faced some challenges due to the different behavior of the two technologies. Let’s see how to implement a subnet-to-subnet 1-to-1 translation with deterministic mappings, using VirtualIPs (DNAT) and Fixed-Port-Range IP-Pools (SNAT). Article originally published by me on Medium on 26 April 2021: Implementing SNAT/DNAT on Fortinet Firewalls has never been straightforward as on other platforms like Checkpoint, in my opinion, at least before the introduction of Central NAT. ![]()
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