Tell me is it really possible to set up a VPN tunnel with a speed of 2 Gbit between Firebox and FortiGate?
Yes, using Link Aggregation of 2 @ 1 Gbps interfaces, or by using a WG firewall set up with a 10 Gbps external interface.
About Link Aggregationhttps://www.watchguard.com/help/docs/help-center/en-US/Content/en-US/Fireware/networksetup/link_aggregation_about_c.html
It is possible on some of the firewalls. I can't speak for FortiGate, but I would assume it is possible there as well.
If you're looking at spec sheets, please keep the following in mind:
-Throughput speeds show aggregate throughput. i.e., all of the VPNs running via the box, not one specific data stream to one firewall.
-One of the most common types of data sent across Branch Office VPNs is SMB (or windows file sharing.) It is not particularly suited to environments with latency, which will almost always occur at least somewhat when traversing a WAN.
-Tests are done using a very specific types of traffic to ensure reproducibility. See IETF's RFC 2544 for more info: https://www.ietf.org/rfc/rfc2544.txt
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