Understanding IMSI Prefix Filtering of GTP Packets

A GPRS support node (GSN) identifies a mobile station (MS) by its International Mobile Station Identity (IMSI). An IMSI consists of three elements: the mobile country code (MCC), the mobile network code (MNC), and the Mobile Subscriber Identification Number (MSIN). The MCC and MNC combined constitute the IMSI prefix and identify the mobile subscriber’s home network, or public land mobile network (PLMN).

By setting IMSI prefixes, you can configure the device to deny GPRS tunneling protocol (GTP) traffic coming from nonroaming partners. By default, a device does not perform IMSI prefix filtering on GTP packets. By setting IMSI prefixes, you configure the device to filter create-pdp-request messages and permit only GTP packets with IMSI prefixes that match the ones you set. The device allows GTP packets with IMSI prefixes that do not match any of the IMSI prefixes that you set. To block GTP packets with IMSI prefixes that do not match any of the IMSI prefixes set, use an explicit wildcard for the IMSI filter, and the drop action should be the last IMSI prefix filtering policy.

When you filter GTP packets based on an IMSI prefix, you must also specify an APN.

Related Topics

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