hile the UPF is connected to the DN via the N6 interface. The N9 interface might be activated to enable a direct communi- cation between UPFs. Both N3 and N6 interfaces implement GTP to identify and forward encapsulated traffic in the CN, while the N6 interface assumes routing plain IP protocol data units (PDUs). Encapsulation consists of adding a GTP-user (GTP-U) header to the IP datagram (i.e. the user data packet T-PDU) and using User Datagram Protocol (UDP)/IP as transport layer. Both IPv4 and IPv6 traffic types are supported, as explained in (3GPP TS 29.281, 2019). The GTP-U header has a variable length that depends on the number of optional fields. The minimum length is 8 bytes and includes the Tunnel Endpoint Identifier (TEID), which is the key element to identify the packet data protocol (PDP) context of the T-PDU of any received packet. However, this protocol does not provide native path differentiation and it is already showing its limitations for some of the 5G use cases, including V2X scenarios [10]. 13.5.2 Segment Routing v6 Recently envisioned as the successor to the GTP protocol, SRv6 uses an IPv6 routing header extension, the Segment Routing Header (SRH), as defined in [11]. Its structure consists of segment lists (SLs), wherein each segment is identified with an IPv6 address, i.e. the Seg- mentID (SID). The current active segment is the destination address of the packet, while the next address is indicated by the SL field of the SRH. The use of segment routing fully enables network programmability, as one can associate a given SID with given processing function behaviors, which may be tailored onto specific applications, such as V2X services. Segment routing enables service providers to support network slicing without any additional protocol [12]. Such functions can be classified into two main categories: endpoint behaviors, which have a local SID to the destination address received, being associated to a processing function in the local node; and transit behaviors, wherein there is no local SID 