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Introduction to GTPv1 Message Filtering and GTP Message Types

Learn about GTPv1 message filters, including message-length and message-type filters. This topic explains how devices process GTP packets, apply inspection policies, and enforce security rules.

A GTP packet contains a message body and the GTP, UDP, and the IP headers. A GTP packet is passed or dropped based on the GTP message filters. The GTP messages are filtered based on the message length and message type.

Types of GTP Message Filters

When the device receives a GPRS tunneling protocol (GTP) packet, it checks the packet against policies configured on the device. If the packet matches a policy, the device inspects the packet according to the GTP configuration applied to the policy. If the packet fails to meet any of the GTP configuration parameters, the device will pass or drop the packets based on the configuration of the GTP inspection object.

A GTP packet consists of the message body and three headers: GTP, UDP, and IP. If the resulting IP packet is larger than the maximum transmission unit (MTU) on the transferring link, the sending Serving GPRS Support Node (SGSN) or gateway GPRS support node (GGSN) performs an IP fragmentation.

By default, the device buffers IP fragments until it receives a complete GTP message, and then inspects the GTP message.

GTP Message-Length Filter

Devices can be configured to drop packets outside the allowed minimum or maximum message length. The message length field in the GTP header indicates the size (in octets) of the GTP payload, excluding GTP, UDP, and IP headers.

  • Default minimum length: 0 bytes

  • Default maximum length: 65,535 bytes

GTP Message-Type Filter

Devices can permit or deny GTP packets based on their message type. By default, all GTP message types are permitted.

  • Filtering applies at the message type level. Denying one message type (e.g., sgsn-context) denies all its related messages (request, response, acknowledge).

  • Message-type filtering can differ by GTP version. For example, a type may be denied in one version but permitted in another.

Example: Set the GTP Message-Length Filter

This example shows how to set the GTP message lengths.

Requirements

No special configuration beyond device initialization is required before configuring this feature.

Overview

In this example, you configure the minimum GTP message length to 8 octets and the maximum GTP message length to 1200 octets for the GTP inspection object.

Configuration

Step-by-Step Procedure

To configure the GTP message lengths:

  1. Specify the GTP profile.

  2. Specify the minimum message length.

  3. Specify the maximum message length.

  4. If you are done configuring the device, commit the configuration.

Supported GTP Message Types

Table 1 lists the GTP messages supported in GTP Releases 1997 and 1999 (including charging messages for GTP) and the message types that you can use to configure GTP message-type filtering.

Table 1: GTP Messages

Message

Message Type

Version 0

Version 1

create AA pdp context request

create-aa-pdp

b

  

create AA pdp context response

create-aa-pdp

b

  

create pdp context request

create-pdp

b

b

create pdp context response

create-pdp

b

b

data record request

data-record

b

b

data record response

data-record

b

b

delete AA pdp context request

delete-aa-pdp

b

  

delete AA pdp context response

delete-aa-pdp

b

  

delete pdp context request

delete-pdp

b

b

delete pdp context response

delete-pdp

b

b

echo request

echo

b

b

echo response

echo

b

b

error indication

error-indication

b

b

failure report request

failure-report

b

b

failure report response

failure-report

b

b

forward relocation request

fwd-relocation

b

b

forward relocation response

fwd-relocation

b

b

forward relocation complete

fwd-relocation

b

b

forward relocation complete acknowledge

fwd-relocation

b

b

forward SRNS context

fwd-srns-context

b

b

forward SRNS context acknowledge

fwd-srns-context

b

b

identification request

identification

b

b

identification response

identification

b

b

node alive request

node-alive

b

b

node alive response

node-alive

b

b

note MS GPRS present request

note-ms-present

b

b

note MS GPRS present response

note-ms-present

b

b

pdu notification request

pdu-notification

b

b

pdu notification response

pdu-notification

b

b

pdu notification reject request

pdu-notification

b

b

pdu notification reject response

pdu-notification

b

b

RAN info relay

ran-info

b

b

redirection request

redirection

b

b

redirection response

redirection

b

b

relocation cancel request

relocation-cancel

b

b

relocation cancel response

relocation-cancel

b

b

send route info request

send-route

b

b

send route info response

send-route

b

b

sgsn context request

sgsn-context

b

b

sgsn context response

sgsn-context

b

b

sgsn context acknowledge

sgsn-context

b

b

supported extension headers notification

supported-extension

b

b

g-pdu

gtp-pdu

b

b

update pdp context request

update-pdp

b

b

updated pdp context response

update-pdp

b

b

version not supported

version-not-supported

b

b

Example: Filter GTP Message Types

This example shows how to permit and deny GTP message types.

Requirements

No special configuration beyond device initialization is required before configuring this feature.

Overview

In this example, for the gtp1 profile, you configure the device to drop the error-indication and failure-report message types for version 1.

Configuration

Step-by-Step Procedure

To permit and deny GTP message types:

  1. Configure the device.

  2. Drop the error indication.

  3. Drop the failure report messages.

  4. If you are done configuring the device, commit the configuration.