 downloaded into a pre-Release-10 SGSN (or even pre-Release-9). As a result, the PDP Type gets treated only as the PDP Type IPv4 and there is no way for the UE to activate a PDP Type IPv6 PDP Context. Actually, the deployment described earlier should never be allowed to happen. A network deployment must take care that the SGSN/MME versions are up to date with the HLR/HSS versions and provisioning, and there is no feature disparity. Some early GGSNs could not handle a configuration where two APNs had the same name and different PDP Types. For their remission there was no 3GPP specification text that would have mandated such configuration prior to Release-8. However, such a limitation effectively makes fallback cases to two single IP ver- sion PDP Contexts instead of a dual-stack one harder. The UE and the network have to be configured with different APNs for each PDN Type instead of having just one. 4.5.3 Dual Address Bearer Flag The DAF is used in GTP-C (interfaces S2b, Gn/Gp, S5/S8, S3, and S11) signaling during the activation of the PDN Connection. Its value is pre-configured by an operator and set by an SGSN/MME when a UE requests a PDN Type IPv4v6 and all SGSNs that the UE may handover to are Release-9 and PDP Type IPv4v6 capable. This is useful during a phased core network migration to fully Release-9 capable SGSNs. There is a strict requirement that when an inter-SGSN RAU or an intra-RAT handover takes place that the PDN Types must match one-to-one. During the migration phase the core network might have a mixture of Release-9 SGSNs, pre-Release-9 SGSNs, and possibly MMEs, and a handover between those should be allowed. Deploying IPv6 in 3GPP Networks The DAF is signaled within the Indication information element in GTPv2 [3]. Within GTPv1 the DAF is found in the Common Flags information element [9]. The absence of the DAF is interpreted as being unset. 4.5.4 Requested PDN Type Handling in a PGW A PGW configuration may also affect the final selection of the PDN Type for a PDN Connection. The configuration is 