 PDP Type, even if the actual addressing information was absent. Even if a complete IPv6 address is included within the information element, a UE must ignore the /64 prefix when the PDP Address information element is received from the network and only extract the IID for the further configuration of the link-local address for the PDP Context (this is specifically stated in multiple 3GPP specifications [12, 13, 25]). Some SGSNs even send an IPv6 link-local address instead of the IPv6 GUA assigned to the PDP Context. Figure 4.23 shows the PDN Address information element [13] used in EPS. It may only appear in the network originated Activate Default EPS Bearer Context Request NAS message. Unlike its GPRS companion, the information element does not carry an IPv6 prefix anymore, just the IID. Furthermore, the PDN Type for requesting a specific type of PDN Connection now has a dedicated PDN Type information element, which can be found in the UE originated PDN Connectivity Request NAS message. Figure 4.24 shows the PDN Type information element. If for any reason a MME does not understand the PDN Type content, it must be treated as PDN Type IPv6 (i.e., 010). Another small detail concerns the EPS and the NAS signaling. Although the GTPv2 information elements (see Figure 4.14 in Section 4.3.2) allows for arbitrary length IPv6 prefix, the PDN Address information element is hardcoded to /64. During the PDN Connection activation, a number of IP level configuration parameters gets exchanged between the UE and the PGW. The configuration information, in addition to IPv4 address and/or IPv6 prefix, is conveyed inside the PCOs [12]. The UE may request, for example, Recursive DNS Server (RDNSS) and P-CSCF addresses, or indicate whether it wants to configure its IPv4 address using DHCPv4. As a response, the PGW returns Octets PDN address IEI (mandatory in current NAS messages thus no code point) Length (5 for IPv4, 9 for IPv6, 13 for IPv4v6) PDN Type (v4 = 001, v6 = 010, Spare '00000' v4v6 = 011) 4-n (15) PDN Address (IPv4, IPv6 IID