FortiCarrier – Configuring GTP

Configuring GTP on FortiOS Carrier

Configuring GTP support on FortiOS Carrier involves configuring a number of areas of features. Some features require longer explanations, and have their own chapters. The other features are addressed here.

GTP support on the Carrier-enabled FortiGate unit

Configuring General Settings on the Carrier-enabled FortiGate unit

Configuring Encapsulated Filtering in FortiOS Carrier

Configuring the Protocol Anomaly feature in FortiOS Carrier

Configuring Anti-overbilling in FortiOS Carrier

Logging events on the Carrier-enabled FortiGate unit

GTP support on the Carrier-enabled FortiGate unit

The FortiCarrier unit needs to have access to all traffic entering and exiting the carrier network for scanning, filtering, and logging purposes. This promotes one of two configurations — hub and spoke, or bookend.

A hub and spoke configuration with the Carrier-enabled FortiGate unit at the hub and the other GPRS devices on the spokes is possible for smaller networks where a lower bandwidth allows you to divide one unit into multiple virtual domains to fill multiple roles on the carrier network. It can be difficult with a single FortiOS Carrier as the hub to ensure all possible entry points to the carrier network are properly protected from potential attacks such as relayed network attacks.

A bookend configuration uses two Carrier-enabled FortiGate units to protect the carrier network between them with high bandwidth traffic. One unit handles traffic from mobile stations, SGSNs, and foreign carriers. The other handles GGSN and data network traffic. Together they ensure the network is secure.

The Carrier-enabled FortiGate unit can access all traffic on the network. It can also verify traffic between devices, and verify that the proper GPRS interface is being used. For example there is no reason for a Gn interface to be used to communicate with a mobile station — the mobile station will not know what to do with the data — so that traffic is blocked.

When you are configuring your Carrier-enabled FortiGate unit’s GTP profile, you must first configure the APN. It is critical to GTP communications — no traffic will flow without the APN.

GTP support on the Carrier-enabled FortiGate unit

The Carrier-enabled FortiGate unit does more than just forward and route GTP packets over the network. It also performs:

  • Packet sanity checking l GTP stateful inspection l Protocol anomaly detection and prevention
  • HA
  • Virtual domain support

Packet sanity checking

The FortiOS Carrier firewall checks the following items to determine if a packet confirms to the UDP and GTP standards:

  • GTP release version number — must be 0, 1, or 2 l Settings of predefined bits l Protocol type l UDP packet length

If the packet in question does not confirm to the standards, the FortiOS Carrier firewall drops the packet, so that the malformed or forged traffic will not be processed.

GTP stateful inspection

Apart from the static inspection (checking the packet header), the FortiOS Carrier firewall performs stateful inspection.

Stateful inspection provides enhanced security by keeping track of communications sessions and packets over a period of time. Both incoming and outgoing packets are examined. Outgoing packets that request specific types of incoming packets are tracked; only those incoming packets constituting a proper response are allowed through the firewall.

The FortiOS Carrier firewall can also index the GTP tunnels to keep track of them.

Using the enhanced Carrier traffic policy, the FortiOS Carrier firewall can block unwanted encapsulated traffic in GTP tunnels, such as infrastructure attacks. Infrastructure attacks involve attempts by an attacker to connect to restricted machines, such as GSN devices, network management systems, or mobile stations. If these attmpts to connect are detected, they are to be flagged immediately by the firewall .


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