IR.21 (Roaming Data Sheet)

Also known as: Roaming Data Sheet, IR21

IR.21 is the GSMA-defined operator roaming information document listing an operator's PLMN identifiers, network element addresses (STPs, GTs, Diameter realms, SEPP FQDNs), SCCP/Diameter/HTTP/2 addressing, protocol variants and roaming testing contacts. IR.21 is used to establish and maintain roaming relationships and, historically, its leakage has enabled targeted SS7 and Diameter attacks against specific operators.

Categories: SignalingRoaming and InterconnectSecurity Controls

IR.21 in context

Signaling protocols carry the control-plane instructions that set up calls, register subscribers, hand over sessions and route SMS. SS7, Diameter, GTP-C and SIP are the four dominant families, and interconnect exposure of any of them is treated by GSMA FS.11 / FS.19 / FS.20 as a top-tier telecom risk.

Roaming and interconnect are where two operators, often with an IPX or GRX carrier in between, exchange signaling and user-plane traffic. Trust boundaries here are the primary attack surface for location tracking, SMS interception and fraud, which is why GSMA now mandates SEPP with PRINS on 5G interconnect.

To place IR.21 in the wider telecom-security picture, review Diameter Interconnect Security, Hybrid KEM, SEPP Security, SS7 Interconnect Security, FS.36 and IBCF.

Related terms

Related topic hubs

  • Roaming Security IPX/GRX interconnect risk, home-routed vs local-breakout, SEPP.
  • Signaling Firewall Unified SS7/Diameter/GTP/SMS signaling firewall framework.
  • SS7 Security SS7/MAP/CAP/SCCP attacks and defenses across 2G/3G interconnect.
  • SS7 Firewall GSMA FS.11 category 1/2/3 SS7 message screening at the STP edge.

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