FortiCarrier Configuring Encapsulated Non-IP End User Address Filtering

Configuring Encapsulated Non-IP End User Address Filtering

Much of the traffic on the GPRS network is in the form of IP traffic. However some parts of the network do not used IP based addressing, so the Carrier-enabled FortiGate unit is unable to perform Encapsulated IP Traffic

Filtering.

Depending on the installed environment, it may be beneficial to detect GTP packets that encapsulate non-IP based protocols. You can configure the FortiOS Carrier firewall to permit a list of acceptable protocols, with all other protocols denied.

The encoded protocol is determined in the PDP Type Organization and PDP Type Number fields within the End User Address Information Element. The PDP Type Organization is a 4-bit field that determines if the protocol is part of the ETSI or IETF organizations. Values are zero and one, respectively. The PDP Type field is one byte long. Both GTP specifications only list PPP, with a PDP Type value of one, as a valid ETSI protocol. PDP Types for the IETF values are determined in the “Assigned PPP DLL Protocol Numbers” sections of RFC 1700. The PDP types are compressed, meaning that the most significant byte is skipped, limiting the protocols listed from 0x00 to 0xFF.

To configure the Encapsulated Non-IP End User Address Filtering, go to Security Profiles > GTP Profile, and edit a GTP profile. Expand Encapsulated Non-IP End User Address Filtering to configure settings. See Encapsulated non-IP end user traffic filtering options.

Configuring the Protocol Anomaly feature in FortiOS Carrier

When anomalies do happen, it is possible for the anomaly to interrupt network traffic or consume network resources ā€” if precautions are not taken. Anomalies can be generated by accident or maliciously, but both methods can have the same results ā€” degrading the performance of the carrier network, or worse.

To configure GTP protocol anomalies, go to Security Profiles > GTP Profile, and edit a GTP profile. Expand the Protocol Anomaly option. See Protocol Anomaly prevention options.

The following are some examples:

  • The GTP header specifies the length of the packet excluding the mandatory GTP header. In GTP version 0 (GSM

09.60), the mandatory GTP header size is 20 bytes, whereas GTP version 1 (GSM 29.060) specifies that the

minimum length of the GTP header is 8 bytes. The GTP packet is composed of the header, followed by Information Elements typically presented in a Type-Length-Value format. It is possible for an attacker to create a GTP packet with a GTP header field length that is incompatible with the length of the necessary information elements.

  • The same concepts are true for GTP version 2 headers even though there are different fields in them.
  • It is similarly possible for an attacker to create a packet with an invalid IE length. Invalid lengths may cause protocol stacks to allocate incorrect amounts of memory, and thereby cause crashes or buffer overflows.

By default the FortiOS Carrier firewall detects these problems, as well as other protocol anomalies, and drops the packets. All protocol anomaly options are set to Deny by default. However, you can change the policy to allow them.


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