1. Telecommunications Essentials John R. Durrett July 5, 2005

2. CISSP CIA Triad ● Confidentiality ● Integrity ● Availability

3. Basic Definitions ● Protocol – a standard set of rules for computer to computer communications – Describes format of messages – Describes way messages are transmitted – Enables different computers to communicate – Allows extensions of existing standards – Typically uses a layered model

4. Layered Architectures ● Utilizes logical groups called layers ● Helps clarify communications process ● Breaks down complexity ● Enables interoperability ● Allows changing of individual layers without changing others ● Makes for easier troubleshooting

5. The OSI Model Physical TransportApplicationSession Presentation Datalink Physical TransportApplicationSession Presentation Datalink Across Network The path messages take Sender Receiver Network Network

6. OSI Layers Communication between apps, user interface, WWW, FTP, etc Semantics, encryption compression Establishes, manages, terminates sessions Sequencing, flow/error control, name/address resolution Routing, network addresses (routers) MAC address, ARP, RARP, ICMP, (bridges) Encoding/decoding digital bits, interface card Physical Network TransportApplicationSession Presentation Datalink

7. TCP/IP Network Layer TransportLayer Application TransportLayer Application TransportLayer Alice Bob Router

8. TCP/IP: The Protocols and the OSI Model Ethernet Token Bus Token Ring FDDI Internet Protocol ARP TELNET FTP SMTP DNS SNMP DHCP DatalinkPhysical Network Transport ApplicationPresentationSession ICMP IGMP RTPRTCPTransmission Control Protocol User Datagram Protocol OSPF RIP

9. Data Encapsulation by Layer Destination Data TCP Header Datagram Packet Application TCP Network Data Link Frame Opens envelopes layer-by-layer

10. Transmission Control Protocol ● Full duplex ● Connection Oriented, packets are sequenced ● Costly in terms of network overhead ● Slower than UDP ● Syn, Ack-Syn, Ack

11. TCP Fields Source portDestination port Sequence number Acknowledgment number Data offset Reserved Window ChecksumUrgent pointer OptionsPadding data URPACKPSHRSTSYNFIN

12. User Datagram Protocol ● Best effort delivery only ● Connectionless ● No sequence, no error correction ● “unreliable” protocol

13. Source Port Destination Port Message Length Checksum Data … UDP Fields

14. Ports PORTUSE 17Quote of the Day 20File Transfer Data 21File Transfer Control 22SSH 23Telnet 25SMTP 53DNS > 1024 “Ports are used in the TCP [RFC793] to name the ends of logical connections which carry long term conversations. For the purpose of providing services to unknown callers, a service contact port is defined. This list specifies the port used by the server process as its contact port. The contact port is sometimes called the "well-known port". RFC793 Source portSource port Destination portDestination port Logical connectionLogical connection Privileged – unprivileged portsPrivileged – unprivileged ports Netstat –naNetstat –na

15. Internet Protocol ● Network Layer Protocol ● Logical ID called an IP address ● IP sender & IP recipient ● Routing decisions based on destination IP address

16. IP Address (IPv4) ● uniquely identifies a computer on a network ● 32 bits, 4 bytes of 8 bits each: xxxxxxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx ● dotted quad notation system ● Example 198.113.201.23 ● There are five classes of addresses: A - E.

17. Identifying a Class AddressIdentifier Network Address Host Address 11110 Class E - Reserved for future use 0 7 bits of network address 24 bits of host address First byte Last three bytes Class A 10 14 bits of network address 16 bits of host address First two bytesLast two bytes 110 21 bits of network address 21 bits of network address 8 bits of host address First three bytes Last byte 1110 Multicast address in the range of 224.0.0.0 - 239.255.255.255 Class B Class C Class D Class E 0-126 128-191 192-223 224-239 240-255 16,277,214 hosts per network ID 254 hosts 65,354 hosts

18. Subnetting ● Each address consists of two components: Network address and Host address ● Determined by Netmask ● 10.21.41.3 = 00001010 00010101 00101001 00000011 ● 255.255.0.0 = 11111111 11111111 00000000 00000000 ● Network address is IP XORed with netmask Customer Site 130.1.0.0 130.1.1.0130.1.2.0130.1.3.0..............130.1.255.0 Internet