How does a DHCP server dynamically assign IP addresses to hosts?

A、 Addresses are permanently assigned so that the host uses the same address at all times．
B、 Addresses are assigned for a fixed period of time． At the end of the period, a new request for an address must be made, and another address is then assigned．
C、 Addresses are leased to hosts． A host will usually keep the same address by periodically contacting the DHCP server to renew the lease．
D、 Addresses are allocated after a negotiation between the server and the host to determine the length of the agreement．

【正确答案】 C

【答案解析】在DHCP租约期限一半时，DHCP客户端会提交租约续订请求到DHCP服务器。如果DHCP服务器在联机状态，那么通常DHCP服务器会接受续订，然后租约周期重新开始。如果DHCP服务器不可用那么DHCP客户端会在剩余一半的租约周期过去后尝试再次续订DHCP租约。如果在租约时间的87．5%过去后DHCP服务器仍然不可用，DHCP客户端会尝试寻找一个新的DHCP服务器，并可能获取一个不同的IP地址。