Network Device 中繼傳輸裝置

-L1：Hub, Repeater
-L2：bridge, switch
-L3：router, L3switch, IP sharing
-L4~L7：Gateway, Firewall, 防毒牆，頻寬分流器，Proxy server
-L7 Server：DHCP, Web, Email, FTP, TFTP, DNS