Computer Science and Engineering Computer System Security CSE 5339/7339 Session 24 November 11, 2004

Computer Science and Engineering Contents  Network Basics (cont.)  Group Work  Security in Networks  Group Work  Allison’s presentation

Computer Science and Engineering Computer Network Basics  Wide Area Networks (WAN)  Metropolitan Area Network (MAN)  Local Area Network (LAN)  System or Storage Area Network (SAN)

Computer Science and Engineering Routing Schemes  Connection-oriented The entire message follows the same path from source to destination.  Connectionless A message is divided into packets. Packets may take different routes from source to destination Serial number

Computer Science and Engineering Network Performance  Gilder’s Law George Gilder projected that the total bandwidth of communication systems triples every twelve months. Ethernet: 10Mbps  10Gbps (1000 times) CPU clock frequency: 25MHz  2.5GHz (100 times)  Metcalfe's Law Robert Metcalfe projected that the value of a network is proportional to the square of the number of nodes Internet

Computer Science and Engineering Internet Internet is the collection of networks and routers that form a single cooperative virtual network, which spans the entire globe. The Internet relies on the combination of the Transmission Control Protocol and the Internet Protocol or TCP/IP. The majority of Internet traffic is carried using TCP/IP packets.

Computer Science and Engineering Country Internet Users Latest Data Population ( 2004 Est. ) % of Population United States209,518,183294,540, % China79,500,0001,327,976, % Japan63,884,205127,944, % Germany45,315,16682,633, % United Kingdom35,089,47059,157, % South Korea29,220,00047,135, % France22,534,96759,494, % Brazil20,551,168183,199, % Italy19,900,00056,153, % Canada16,841,81132,026, %

Computer Science and Engineering ISO OSI Network Model Application Presentation Session Transport Network Data Link Physical Application Presentation Session Transport Network Data Link Physical LAN Internet

Computer Science and Engineering Group Work (Simple example) Show how a message is sent from point A to point B on a network through the seven layers. You might want to look at the example on page 375.

Computer Science and Engineering Mail ftp Telnet Transmission Control Protocol (TCP) Internet Protocol (IP) Ethernet Token ring TCP/IP

Computer Science and Engineering TCP/IP Packets Physical Header IP Header TCP Header message

Computer Science and Engineering Addressing  MAC (Media Access Control) address Every host connected to a network has a network interface card (NIC) with a unique physical address.  IP address IPv4  32 bits ( ) IPv6  128 bits

Computer Science and Engineering Routing  Routers  Routing Tables  Example

Computer Science and Engineering IP Protocol  Unreliable packet delivery service  Datagram (IPv4) Service TypeVERSHLENTOTAL LENGTH IDENTIFICATIONFLAGSFRAGMENT OFFSET TIME TO LIVEPROTOCOLHEADER CHECKSUM SOURCE ADDRESS DESTINATION ADDRESS PADDINGOPTIONS (IF ANY) DATA

Computer Science and Engineering Group Work Discuss possible attacks

Computer Science and Engineering Attacks  IP Spoofing  Teardrop attacks

Computer Science and Engineering ICMP (Internet Control Message Protocol)  Transmit error messages and unusual situations  Different types of ICMP have slightly different format TypeCodeCHECKSUM Unused (must be zero) DATA: Header and 1 st 64 bits of offending datagram ICMP time-exceeded message

Computer Science and Engineering ICMP (Echo request/reply)  Transmit error messages and unusual situations  Different types of ICMP have slightly different format TypeCodeCHECKSUM Sequence number DATA (optional) ICMP Echo Request/Reply Message Identifier

Computer Science and Engineering Ping of Death Attack  Denial of service attack (1 st in 1996)  Some systems did not handle oversized IP datagrams properly  An attacker construct an ICMP echo request containing 65,510 data octets and send it to victim  The total size of the resulting datagram would be larger than the octet limit specified by IP  System would crash

Computer Science and Engineering SMURF  Attacker send echo request message to broadcast address  Attacker also spoofs source address in the request Intermediary Attacker Victim

Computer Science and Engineering UDP (User Datagram Protocol) CHECKSUM (optional) DATA LENGTH DESTINATION PORTSOURCE PORT  From one application to another (multiple destinations)  Port  positive integer (unique destination)

Computer Science and Engineering Group Work Discuss possible attacks

Computer Science and Engineering TCP CODE BITSHLENRESVWINDOW URGENT POINTER SEQUENCE NUMBER PADDINGOPTIONS (IF ANY) DATA CHECKSUM DESTINATION PORTSOURCE PORT Acknowledgment  Reliable delivery  TCP messages are sent inside IP datagrams

Computer Science and Engineering Group Work Discuss possible attacks

Computer Science and Engineering Wired Backbone with Mobile nodes Fixed Communication Network Fixed Host Fixed host Fixed Host Base Station Wired Backbone Mobile Host

Computer Science and Engineering Wireless Multi-hop Backbone Mobile Host

Computer Science and Engineering Hybrid backbone Fixed Communication Network Fixed Host Fixed host Fixed Host Base Station Wired Backbone Mobile Host Wireless Multi-hop Backbone Mobile Host Hybrid Backbone Mobile Host

Computer Science and Engineering Mobile IP (Cont.) Arbitrary Topology of Routers and Links Home Agent Mobile Host at Home Foreign Agent Mobile Host visiting A foreign subnet Home subnet Foreign subnet