Technical Tip: How to prevent IPv6 addresses from using NAT64

There are 2 options to prevent IPv6 addresses from using NAT64 policies

• In the Virtual IP, specify the range of allowed IPv6 addresses in the source filter. In this screenshot, 2001:ab::20 is not in the range so it will be prevented from usingNAT64:

• Use an IPv6 address group as a source in the NAT64 firewall with source-negate enabled, which means that all IPv6 addresses will be allowed except for the specified source:

config firewall policy
    edit 1
        set name "nat64"
        set srcintf "port5"
        set dstintf "WAN1"
        set action accept
        set nat64 enable
        set srcaddr6 "2001:ab::20"
        set dstaddr6 "vip64"
        set schedule "always"
        set service "ALL"
        set ippool enable
        set poolname "vip64"
        set srcaddr6-negate enable
    next
end

All IPv6 addresses will be allowed except for 2001:ab::20.. It is possible to have a range or a list of IPv6 addresses.

Related article:

Simplify NAT46 and NAT64 policy and routing configurations - FortiGate documentation.