You are encountering connectivity problems caused by intermediate devices blocking IPsec traffic. In which two ways can you effectively resolve the…

When intermediate devices like firewalls or NAT routers block IPsec traffic, two primary methods can resolve the issue. First, switching to SSL VPN (Option A) is highly effective. SSL VPN encapsulates traffic within SSL/TLS, typically using TCP port 443, which is standard for HTTPS traffic and almost universally permitted through network devices. This bypasses blocks on IPsec-specific protocols and ports (ESP, UDP 500/4500).

Second, some connectivity problems arise when intermediate devices drop large, fragmented IKE packets, which can occur during certificate-based authentication. Enabling IKE fragmentation (Option B) allows the FortiGate to split large IKE messages into smaller ones, preventing them from being dropped by these devices and resolving the connectivity issue.

C. The network topology (hub-and-spoke) is irrelevant to solving the problem of blocked ports. The core solution is using SSL VPN, which is more accurately described in option A.

D. Switching to IKEv2 does not solve the problem, as it uses the same ports (UDP 500/4500) and protocol (ESP) as IKEv1. If these are being blocked, IKEv2 will fail just as IKEv1 would.

1. Fortinet FortiOS 7.0.0 Administration Guide, Chapter: SSL VPN, Page 1031: "SSL VPN is a flexible remote access solution... It is an alternative to IPsec VPN that is often easier to configure and is not susceptible to the same network blocking issues that IPsec VPN can experience." This supports using SSL VPN to bypass IPsec blocking issues (Option A).

2. Fortinet FortiOS 7.0.0 Administration Guide, Chapter: IPsec VPN > IKEv2 fragmentation, Page 978: "Some network devices may drop IKE messages that are fragmented. To avoid this, you can enable IKE fragmentation on the FortiGate to allow the IKE messages to be split into smaller messages so that they do not need to be fragmented." This directly supports enabling fragmentation to resolve blocking by intermediate devices (Option B).

3. Fortinet FortiOS 7.0.0 Cookbook, IPsec VPN with IKEv2, Section: "To configure the IPsec VPN at the head office": The configuration steps demonstrate that IKEv2 utilizes UDP ports 500 and 4500, confirming that it is subject to the same port-blocking issues as IKEv1 (making Option D incorrect).