Internet-Security.com UDP port 2123 details

UDP port 2123 is the well-known port for the GPRS Tunneling Protocol Control plane (GTP-C), per IANA (“gtp-control”) and 3GPP specs.
In 2G/3G networks, GTPv1-C on UDP/2123 is used between SGSN and GGSN on the Gn/Gp interfaces; real deployments include Ericsson SGSN/GGSN, Nokia/NSN, and Huawei core nodes.
In LTE/EPC, GTPv2-C on UDP/2123 is used on S11 (MME↔SGW) and S5/S8 (SGW↔PGW); examples include Cisco ASR 5000/5500 (StarOS), Ericsson MME/EPG, Nokia MME/SGW/PGW, and Huawei EPC.
Open-source mobile cores also use it, such as Open5GS (MME/SGW/PGW on S11/S5/S8), srsRAN’s srsEPC, and Osmocom’s OsmoSGSN/OsmoGGSN.
Some 5G deployments still use UDP/2123 for LTE interworking/roaming via GTPv2-C on S5/S8 with EPC anchors (e.g., Mavenir and Affirmed Networks vEPC).
Security note: Exposed GTP-C on UDP/2123 has been abused in the wild to manipulate sessions or cause DoS on misconfigured gateways; telecom guidance (e.g., GSMA) recommends strict filtering and never exposing it to the public internet.

UDP 2123