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

A.允許unrestricted訪問到console或VTY口
B.用防火墻去限制外網(wǎng)的網(wǎng)絡(luò)設(shè)備訪問
C.因?yàn)閿?shù)據(jù)被自動(dòng)加密，所以總是允許使用TELNET命令訪問網(wǎng)絡(luò)設(shè)備的命令行
D.使用SSH或其他加密、認(rèn)證機(jī)制去訪問設(shè)備的配置
E.為了避免丟失密碼，所以不對(duì)密碼進(jìn)行加密（明文）