Assume IPv6 is used to support mobile IP network on campus. To speed up the process of getting a care-of address, one suggests to use the auto-configuration function provided by IPv6. The idea is that each device will use its physical address for the host field and each mobile router (called agent) will periodically broadcast a packet to its broadcast domain. When a mobile device moves into a new broadcast domain, the device can figure out its new IPv6 address without using a DHCP protocol. Explain why that is the case.