In an ADVPN (Auto-Discovery VPN) network, a dynamic VPN tunnel is established on-demand between spokes to optimize traffic flow and reduce latency.
Process:
1. Traffic Initiation:
A client behind Spoke-1 sends traffic to a device behind Spoke-2.
The traffic initially flows through the hub, following the pre-established overlay tunnel.
2. Hub Detection:
The hub detects that Spoke-1 is communicating with Spoke-2 and determines that a direct shortcut tunnel between the spokes can optimize the connection.
3. Shortcut Offer:
The hub sends a "Shortcut Offer" message to Spoke-1, informing it that a direct dynamic tunnel to Spoke-2 is possible.
4. Tunnel Establishment:
Spoke-1 and Spoke-2 then negotiate and establish a direct IPsec tunnel for communication.

Unlike IPS or antivirus databases, FortiGate does not store a full web filter database locally.
Instead, FortiGate queries FortiGuard (or FortiManager, if configured) dynamically to classify and filter web content in real time.
Key points:
Web filtering works on a cloud-based model:
When a user requests a website, FortiGate queries FortiGuard servers to check its category and reputation.
The response is then cached locally for faster lookups on repeated requests.
No local web filter database version:
Unlike IPS and antivirus, which download and store signature updates locally, web filtering relies on cloud-based queries.
This is why no database version appears in the GUI.
Flow mode vs Proxy mode:
In proxy mode, FortiGate can cache some web filter data, improving performance. In flow mode, all queries happen dynamically, with no locally stored database.

The diagram shows a multi-area OSPF network where:
FortiGate A is in OSPF Area 0 (Backbone area).
FortiGate B is in OSPF Area 0.0.0.1 and is connected to an RIP network.
To ensure that OSPF Area 0 (0.0.0.0) learns routes from the external RIP network, FortiGate B must redistribute RIP routes into OSPF.
Steps to achieve this:
1. Enable route redistribution on FortiGate B to inject RIP-learned routes into OSPF.
2. This allows OSPF Area 0.0.0.1 to forward RIP routes to OSPF Area 0 (0.0.0.0), making the external network visible.

When using IPsec VPNs and VXLAN, additional headers are added to packets, which can exceed the default 1500-byte MTU. This can lead to fragmentation issues, dropped packets, or degraded performance.
To resolve this, the MTU (Maximum Transmission Unit) should be adjusted only if all devices in the network path support it. Otherwise, some devices may still drop or fragment packets, leading to continued issues.
Why adjusting MTU helps:
VXLAN adds a 50-byte overhead to packets.
IPsec adds additional encapsulation (ESP, GRE, etc.), increasing the packet size. If packets exceed the MTU, they may be fragmented or dropped, causing intermittent connectivity issues.
Lowering the MTU on interfaces ensures packets stay within the supported size limit across all network devices.

ADVPN (Auto-Discovery VPN) 2.0 is the optimal solution for enabling direct spoke-to-spoke communication without passing through the hub, while also allowing automatic link selection based on quality metrics.
Dynamic Direct Tunnels:
ADVPN 2.0 allows spokes to establish direct IPsec tunnels dynamically based on traffic patterns, reducing latency and improving performance.
Unlike static VPNs, spokes do not need to pre-configure tunnels for each other.
Automatic Link Optimization:
ADVPN 2.0 monitors the quality of multiple internet connections on each spoke. It automatically switches to the best available connection when the primary link degrades or fails.
This is achieved by dynamically adjusting BGP-based routing or leveraging SD-WAN integration.