GTP PROTOCOL- the ultimate telecom security

INTRODUCTION-

A collection of IP-based communication protocols known as GPRS Tunnelling Protocol (GTP) is used to transmit general packet radio service (GPRS) via radio networks such as GSM, UMTS, LTE, and 5G NR. GTP and Proxy Mobile IPv6-based interfaces are provided on several interface points in 3GPP architectures. The GPRS core network uses GTP-C for signalling between serving GPRS support nodes and gateway GPRS support nodes (GGSN) (SGSN). Within the GPRS core network, between the radio access network and the core network, user data is transported using GTP-U. Our Secgen developers design the GTP protocol, and we provide technical background on how GTP works. Going more deeply into this, any IPv4, IPv6, or PPP formatted packets may be used to convey user data.GTP comprises the following separate protocols: GTP - C, GTP-U. 



GTP STANDARDIZATION - 


GTP was first standardized by ETSI (GSM standard 09.60). When the UMTS standards were developed, this was transferred to the 3GPP, which kept it as 3GPP standard 29.060 as of 2005. GTP employs the same message structure, but along with the specified forms for the charging data it transfers, standard 32.295 also covers its unique uses.

GTPv1/v0 interworking is deprecated in later versions of TS 29.060; therefore, there is no fallback if the GSN does not support the higher version.GTPv2 specifically disallows a fallback to GTPv0 but provides a fallback to GTPv1 via the older "Version Not Supported" mechanism.



GTP PROTOCOL STACK - 


GTP can be used with UDP or TCP. GTP-U is also used to transfer user data from the RNC to the SGSN in UMTS networks. However, in this scenario, signalling is done utilizing RANAP instead of GTP-C.

There are three defined versions as of 2018: 0, 1, and 2. Versions 0 and 1 have very different structures. In version 0, the signalling and tunnelling protocols are integrated into a single port to create the tunnels by enabling the PDP context. 

Versions 1 and 2 are two protocols: GTP-C for control and TUN for user data tunnelling (called GTP-U). Only in GTP-C does GTP version 2 differ from version 1. The 3GPP specified improvements to GTP-C for EPS in version 2 to facilitate bearer handling.

The stack goes like this :

  • Application Protocols

  • IP (user)

  • GTP

  • UDP

  • IP

  • Layer 2 (e.g., WAN or Ethernet)

  • GTP-U protocol stack 



WHAT'S INSIDE THE GPRS CORE NETWORK? 


The GPRS core network uses GTP as its main protocol. The protocol enables end users of a GSM or UMTS network to move from one location to another while maintaining an Internet connection as if from the GGSN. It transfers the subscriber's data from the SGSN managing their session to the GGSN.


GSNs (GGSNs and SGSNs combined) monitor UDP port 2123 and port 2152 for GTP-C and GTP-U communications, respectively. This communication occurs in a single network, but in the case of international roaming, it happens internationally across a GPRS roaming exchange. 


The GPRS core network employs three types of GTP-


  1. GTP-U- It allows user data transfer in distinct tunnels for each PDP context

  2. GTP-C is used for control purposes, such as creating and deleting PDP contexts and verifying GSN reachability changes, such as when subscribers switch between SGSNs.

  3. GTP' for the charging function's data transfer from GSNs. 


COGNIZANT OF GTP TRAFFIC -


A GPRS tunnelling protocol (GTP) tunnel is an exchange route for data between two hosts between two GPRS support nodes. The GTP control plane (GTP-C) and GTP user plane make up the GTP tunnel (GTP-U). A service gateway GPRS support node (SGSN), a gateway GPRS support node (GGSN), an SGSN, and a mobility management entity build a GTP tunnel for a user device using the GPRS Tunneling Protocol (GTP) (MME). To send packets to the GGSN through the GTP tunnel, the SGSN first receives them from the user equipment and encapsulates them in a GTP header. After the GGSN receives the packets, they are decapsulated and forwarded to the external host. 



KNOWLEDGE OF GTP-U INSPECTION - 


Security audits are carried out on GTP-U packets using the GPRS Tunneling Protocol User Plane (GTP-U) inspection. When GTP-U inspection is enabled, the GPRS support node (GSN) is shielded from a GTP-U attack, and the invalid GTP-U packets GTP-U inspection may include checks on GTP-in-GTP packets, end-user authorization, packet sequence validity, and tunnel validity once it is enabled and depending on the device configuration.


The numerous GTP-U inspections that are carried out on the traffic are listed below:


  • The GTP-U module verifies GTP-U packet matching to a GTP tunnel. The GTP-U packet is dropped if no tunnels match the one it was sent over.


  • Checking GTP in GTP- The GTP module in the SPU checks to ensure the GTP-U payload isn't a GTP packet. A GTP packet is lost if it is present in the payload.

  • End-user address check- The GTP-U module then looks for the end-user address if the user tunnel for the GTP-U packet is located. The GTP-U packet is dropped if the end-user address and the GTP-U payload don't match. 

  • Checking the sequence number: The GTP-U module verifies the sequence number of the GTP-U packet to the series number stored in the GTP-U tunnel. The GTP-U packet is settled if it is outside the specified range.



GTP TUNNEL ENHANCEMENTS: AN UNDERSTANDING -


A GPRS tunnelling protocol (GTP) tunnel is an exchange route for data between two hosts between two GPRS support nodes. Both the GTP control plane (GTP-C) and the GTP user plane make up the GTP tunnel (GTP-U). The serving GPRS support node and the gateway GPRS support node communicate using GTP-C. At the same time, the user plane traffic is routed and encapsulated via the GTP-U tunnel across several signalling interfaces. To prevent GTP tunnel timeout problems, GTP handling has been improved to update the GTP tunnel and session lifetime.

Even when data traffic continues through the tunnels when the GTP-U inspection is off, the timer value expires, and the GTP-U tunnel cannot be refreshed. As a result, all GTP tunnels time out.

Even if the GTP user validation is turned off, the GTP-U traffic can refresh the GTP tunnel to prevent timeout problems. Only GTPv1 and GTPv2 tunnels can be refreshed by GTP-U traffic; GTPv0 tunnels. 


EXPERTS AT SECGEN : 


The GTP protocol is a collection of IP-based communication protocols that transmit general packet radio service (GPRS) through radio networks such as GSM, UMTS, LTE, and 5G NR. Our experts provide the best service and design GTP protocol for tunnelling and encapsulating data units and control messages in GPRS. Our expertise is at your disposal to help you in any state. 



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