3GPP 38.300 v19.3.0 — the document's own text
8.3 User Data Transport on the CN-RAN Interface
Taught in 8. Where the radio network meets the core (TSG RAN — the group that specifies the radio, in depth).
The core network may provide two transport layer addresses of different versions to enable that a NG-RAN node can select either IPv4 or IPv6.