TCP/IP Concepts Review. Ed Crowley

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1 TCP/IP Concepts Review Ed Crowley 1

2 Objectives At the end of this unit, you will be able to: Describe the TCP/IP protocol stack For each level, explain roles and vulnerabilities Explain basic IP addressing concepts including ports, protocols, and subnetting 2

3 TCP/IP Overview Transmission Control Program/Internet Protocol Worlds most widely used protocol Vint Cerf aka father of the Internet TCP/IP Vulnerabilities Lack of identification and authentication In design, no security goals TCP/IP Four layered stack Application Transport (Host to Host) Internet(work) Network Interface 3

4 Levels of Data Structures At the Application Level, Stream or Message At the Transport Level, TCP Segment or UDP Datagram At the IP Level, Datagram At the Media Level, Frame 4

5 Transmit and receive data flows 5

6 Layers Described 6

7 Application Layer Interface between application program and lower-layer protocols Application program is what you see and touch Includes HTTP FTP TFTP SNMP SMTP 7

8 TCP/IP Application Protocols 8

9 Transport Layer TCP Encapsulates TCP data into segments TCP is connection-oriented TCP connections begin with a three-way handshake Computer A sends a SYN packet Computer B replies with a SYN-ACK packet Computer A replies with an ACK packet UDP Encapsulates UDP data into datagrams UDP is connectionless SSL also operates at this level 9

10 TCP Segment Headers Critical components: Flags Ports source and destination Initial Sequence Number (ISN) To identify vulnerabilities, can be (actively) abused NMap Hping Other packet shapers 10

11 TCP Header 11

12 TCP Flags Each flag is one bit Either 0 (off) or 1 (on) Six flags SYN: synchronization ACK: acknowledge PSH: push URG: urgent RST: reset FIN: finish 12

13 Initial Sequence Number (ISN) 32-bit number Tracks packets received Enables reassembly of large packets Set on steps 1 and 2 of the TCP three-way handshake 13

14 Transport Level Ports Port Logical, connection component Typically used to map a packet to a running process Two socket components (IP:Port) Port numbers are 16-bit integers 2 16 X 2 possible ports Both source and destination ports are utilized Enables unneeded services to be identified Unneeded open ports represent, potentially serious, vulnerabilities 14

15 Port Categories Well-known ports are defined as the first (lower) 1024 (Numbered ) ports Well known means that they have an assigned service In Linux, only privileged system or root processes can use lower level ports Example: HTTP uses port 80 Internet Assigned Numbers Authority (IANA) maintains well-known ports list (www.iana.org) Ports 1024 to are called the Registered Ports Ports to are called Dynamic or Private Ports 15

16 TCP Port Examples Ports 20 and 21 File Transfer Protocol (FTP) Use for sharing files over the Internet Requires a logon name and password Port 25 Simple Mail Transfer Protocol (SMTP) servers listen on this port Port 53 Domain Name Service (DNS) Facilitates connection to Web sites using URLs instead of IP addresses Port 80 Hypertext Transfer Protocol (HTTP) Used when connecting to a Web server 16

17 User Datagram Protocol (UDP) Fast, unreliable (connectionless) transport layer protocol No delivery verification Does not even check that receiver is listening Higher TCP/IP stack layers may provide reliability 17

18 Internet Layer Responsible for: 1. Logical addressing and 2. Routing packets to their destination Uses a logical IP addresses IP is connectionless 18

19 IP Datagram Protocol field 1:ICMP, 6:TCP, 17:UDP 19

20 Internet Layer Nothing can be directly sent to a logical (IP) Address. Information can only be directly sent to physical i.e. MAC Addresses ARP translates between IP and MAC Addresses DHCP offers IP configuration services 20

21 ICMP Internet Control Message Protocol (ICMP) Used to send messages relating to network operations Aides network troubleshooting Example commands include: Ping Traceroute Note: Can be misused as in a Smurf DoS attack 21

22 IPv4 Address Four bytes, 32 bits Two components Network address Host address Classes Class A Class B Class C 22

23 IPv6 Described in RFC 2460 Uses 128 bit address Space for individual addresses 64 bit Host address with 64 bit Network address Mandates IPSec support 23

24 IPv4 Address Classes 24

25 Class A IP Address Class A First byte network address Last three bytes host address Supports more than 16 million host computers Limited number of Class A networks Format: network.node.node.node 25

26 Class B IP Addressing Class B First two bytes for network address Last two bytes host address Supports more than 65,000 host computers Assigned to large corporations and Internet Service Providers (ISPs) Format: network.network.node.node 26

27 Class C IP Addressing Class C First three bytes for network address Last byte for host address Supports up to 254 host computers Usually available for small business and home networks Format: network.network.network.node 27

28 Subnetting Subnetting Each network can be assigned a subnet mask Helps separate the network address bits from the host address bits RFC

29 Questions??? 29

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