# Protocol Summary - Computer Networks ## Application Layer Protocols HTTP - HyperText Transfer Protocol - port 80 - transfers web pages from server to browser - stateless request response protocol HTTPS - HTTP Secure - port 443 - HTTP with TLS encryption - used for secure web browsing FTP - File Transfer Protocol - port 21 control port 20 data - transfers files between client and server - has active and passive modes SSH - Secure Shell - port 22 - encrypted remote access to computers - replaces Telnet - supports key based authentication Telnet - port 23 - unencrypted remote access - insecure, replaced by SSH SMTP - Simple Mail Transfer Protocol - port 25 and 587 - sends email between mail servers and from client to server POP3 - Post Office Protocol version 3 - port 110 - downloads email from server to client and deletes from server IMAP - Internet Message Access Protocol - port 143 - syncs email across multiple devices keeping messages on server DNS - Domain Name System - port 53 UDP for queries TCP for zone transfers - resolves domain names to IP addresses DHCP - Dynamic Host Configuration Protocol - port 67 server port 68 client - automatically assigns IP addresses and network configuration SNMP - Simple Network Management Protocol - port 161 - monitors and manages network devices NTP - Network Time Protocol - port 123 - synchronizes clocks across network devices ## Transport Layer Protocols TCP - Transmission Control Protocol - connection oriented - reliable ordered delivery - three way handshake - flow control - congestion control - used for HTTP FTP SSH email UDP - User Datagram Protocol - connectionless - unreliable but fast - no handshake no acknowledgment - used for DNS DHCP streaming gaming VoIP ## Network Layer Protocols IP - Internet Protocol - provides logical addressing and routing - IPv4 32 bit addresses IPv6 128 bit addresses ICMP - Internet Control Message Protocol - error messages and diagnostics - used by ping and traceroute ARP - Address Resolution Protocol - resolves IP addresses to MAC addresses within local network RARP - Reverse ARP - resolves MAC addresses to IP addresses - obsolete replaced by DHCP OSPF - Open Shortest Path First - link state interior routing protocol - uses cost metric based on bandwidth RIP - Routing Information Protocol - distance vector routing protocol - hop count metric maximum 15 hops BGP - Border Gateway Protocol - exterior routing protocol between autonomous systems - path vector algorithm IGMP - Internet Group Management Protocol - manages multicast group membership ## Data Link Layer Protocols Ethernet - IEEE 802.3 - wired LAN standard - CSMA/CD media access - MAC addressing - most common LAN technology WiFi - IEEE 802.11 - wireless LAN standard - CSMA/CA media access - multiple versions with increasing speeds PPP - Point to Point Protocol - encapsulates network layer protocols for transmission over serial links HDLC - High Level Data Link Control - bit-oriented protocol for point to point and multipoint connections ## Security Protocols TLS - Transport Layer Security - encrypts data in transit - used for HTTPS email FTPS - replaced SSL IPSec - Internet Protocol Security - encrypts and authenticates IP packets - used for VPNs WPA2 - WiFi Protected Access 2 - encrypts WiFi communications - uses AES encryption WPA3 - latest WiFi security standard - stronger against dictionary attacks - mandatory for new WiFi devices