Understanding GTP Sequence Number Validation

You can configure the device to perform sequence-number validation.

The header of a GPRS tunneling protocol (GTP) packet contains a Sequence Number field. This number indicates to the gateway GPRS support node (GGSN) receiving the GTP packets the order of the packets. During the packet data protocol (PDP) context-activation stage, a sending GGSN uses zero (0) as the sequence number for the first G-PDU it sends through a tunnel to another GGSN. The sending GGSN increments the sequence number for each following G-PDU it sends. The value resets to zero when it reaches 65,535.

During the PDP context-activation stage, the receiving GGSN sets its counter to zero. Subsequently, whenever the receiving GGSN receives a valid G-PDU, the GGSN increments its counter by one. The counter resets to zero when it reaches 65,535.

Normally, the receiving GGSN compares the sequence number in the packets it received with the sequence number from its counter. If the numbers correspond, the GGSN forwards the packet. If they differ, the GGSN drops the packet. By implementing a Juniper Networks device between the GGSNs, the device can perform this validation for the GGSN and drop packets that arrive out of sequence. This feature helps conserve GGSN resources by preventing the unnecessary processing of invalid packets.

Related Topics

JUNOS Software Feature Support Reference for SRX Series and J Series Devices