n employing route optimization). In MIPv6, we can pig- gyback mobile IP specific information onto data packets. MIPv4 has the ability to provide smoother handover as an add-on feature that forms part of the route optimization protocol. In contrast support for smoother handover is an integral part of the MIPv6 specification. In MIPv4 we require reverse tunnelling to avoid ingress filtering problems (where firewalls drop the mobile's outgoing packets) since packets are sent with the home address as the source. In MIPv6 packets may be sent with the COA as the source address, hence there should not be any problems with ingress filtering. MIPv4 provides its own security mechanisms whereas MIPv6 employs the IPsec protocol suite. To adequately assess the evolution and compatibility issues between MIPv4 and MIPv6 when applying to UMTS networks, we have to address each of above differences. We have to address additional issues when preparing the deployment or migration between IPv4 and IPv6 networks in general [8]. 9.10.2.1 Reverse Tunnels In Ipv4 we need reverse tunnels (that is tunnels from the FA to the HA), both for remote network secure access and to avoid packet drops due to ingress filtering. Ingress filter- ing allows tracking of malicious users attempting denial of service attacks based on topologically inconsistent source address spoofing In mobile IPv6, we do not need reverse tunnels to avoid problems with ingress filters. However they may still be beneficial when the ME is concerned about location privacy. The MN may use the care-of address as sender address but that is not required. The UMTS Network and Radio Access Technology 9.10.2.2 Use of Route Optimization Route optimization reduces delays between the CH and ME, and it also reduces the load placed on HAs. Nonetheless, in MIPv4 it adds to the complexity of the HA and requires security associations between the HA and all CHs. Furthermore it still requires packets to be tunnelled from the CH to the FA-COA. In contrast, route optimization in MIPv6 removes th