Currently, various efforts are being performed on specifying distributed mobility management (DMM) for IPv6 mobile networks. DMM is expected to eliminate the limitations of the current IPv6 mobility protocols and to cope with the rapid increase in mobile data traffic. In current DMM approaches, the mobility anchoring is distributed at the access router level and the mobile node changes dynamically the mobility anchor for new sessions. Although such approaches avoid any network bottleneck and allow optimal routing in most cases, they lack reachability support since the mobile node has no permanent IPv6 address. In this paper, we consider one of the DMM approaches, dynamic mobility anchoring, and study the usage of session initiation protocol (SIP) for providing reachability support. After defining different SIP-based location update modes, we carry out a comparative cost analysis considering new performance metrics related to the processing loads at each network entity. We consider the location update loads on the location server as well as the context, signaling, and tunneling loads on a mobility anchor. We investigate the different modes in several scenarios, allowing the mobile network operator to adopt the preferred mode depending on their architecture