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

A.spanning-tree backbonefast
B.spanning-tree uplinkfast
C.spanning-tree portfast
D.spanning-tree cost512

A.拒絕服務(wù)器攻擊
B.IP地址欺騙
C.DOS TCP SYN攻擊
D.DOS smurf攻擊

A.802.3ad
B.802.1w
C.802.1Q
D.802.1d

A.每個(gè)用戶的挑戰(zhàn)驗(yàn)證機(jī)制
B.簡(jiǎn)化路由器對(duì)ACL的處理
C.降低網(wǎng)絡(luò)黑客對(duì)網(wǎng)絡(luò)的攻擊機(jī)會(huì)
D.在不損害其他安全配置的前提下，可以動(dòng)態(tài)的讓用戶穿越防火墻