A.物理層 B.數(shù)據(jù)鏈路層 C.網(wǎng)絡(luò)層 D.傳輸層
A.一次B.二次C.三次D.四次
A.255.255.255.224 B.255.255.255.192 C.255.255.255.254 D.255.285.255.240