TCP/IP Basics - SRTY1021 PDF

TCP/IP Basics  A computer is assigned an IP address when it is connected to a network Manual (static) or automatically (DHCP) Connectivity to a computer on the network can be tested with the PING command When a reply is received there is an active path to the other computer Ping is one co...

TCP/IP Basics  A computer is assigned an IP address when it is connected to a network Manual (static) or automatically (DHCP) Connectivity to a computer on the network can be tested with the PING command When a reply is received there is an active path to the other computer Ping is one command that is part of the Internet Control Messaging Protocol (ICMP) IP addressing will be examined in detail in the INFO1220 Networking course SRTY1021 3  Applications and programs running on a computer are assigned a port number by the TCP/IP service Port numbers are assigned to progams by the Internet Assigned Numbers Authority (IANA) Port 80 – HTTP protocol used by web server Port 443 – HTTPS protocol for encrypted packet to web server Port 23 – Telnet protocol (terminal console connection) Port 21 – File Transfer Protocol (FTP) TCP/IP service will be studied in detail in this and other courses in the CYB program SRTY1021 4  A computer with a single IP address may be running several applications which have been assigned different TCP port numbers Multitasking When a computer wants to establish a connection to a service on another computer it sends a packet to the other computer IP address and port number assigned to the program To connect to a web server an IP packet is sent to port 80 The combination of an IP address and a port is a socket 192.168.1.16:80 The command http:\\192.168.1.16 assumes the destination port number is 80 because 80 is the assigned port number for the HTTP (web) protocol SRTY1021 5  There are 65536 available port numbers Port field in TCP header is 16 bits long Port numbers are arranged into 3 ranges 0 - 1023 are the Well Known port number Assigned to the original TCP/IP applications such as FTP 1024 - 49151 are Registered Ports Assigned to newer applications 49152 - 65535 are Dynamic ports Assigned by your operating system when a program such as Chrome browser is started SRTY1021 6  The operating system assigns a port number to applications that do not have a well known port number Port 80 is reserved for web servers When the browser is opened it is assigned a port number at random in the range 49152 – 65535 Some documentation refers to the ephemeral range If the browser is opened a second time another port number will be assigned to that instance of the browser SRTY1021 7  A computer may have several TCP/IP connections established at the same time on a single IP address The current connections can be viewed with the command netstat Netstat has many command options to list the connection information details SRTY1021 8 SRTY1021 9  Windows has some well-known services that are listening by default in the upper range of port numbers wininit.exe 49152 event log service 49153 schedule service 49154 services.exe 49155 lsass.exe 49156 The netstat command with –abn option will display the service running the listening port Shown on next slide SRTY1021 10 SRTY1021 11