CSCI 6781 Advanced Computer Networks

1. CSCI 6781Advanced Computer Networks Ram Dantu Introduction: Part-1

2. Course Overview Introduction: Part-1

3. Syllabus • This class IS about... • Recent advances in Computer Networks • New developments in Physical Layer, Layer 2 (ATM/MPLS), Layer 3 (mobile IP, ForCES), Layer 4 (SCTP) and application layers like SIP, MIDCOM, MobileIP, etc. • Vulnerability of these protocols, threat models • Risk analysis using behavior, attack profile and graph theory • Working together and learning together …. Introduction: Part-1

4. Background • My background • Your background, thesis topic and why are you talking this course • Need some course to finish the degree • Want to be network security engineer • Want to be a hacker • Check your email often (atleast twice a day) • Office Hours and appointment (available most of the week days, get an appointment) Introduction: Part-1

5. Grading Introduction: Part-1

6. HomeWork1 • Document the state diagram and a short description for two protocols. In addition, survey and collect exploits for at least two protocols. You can use CERT, NIST, NSA, DHS or any other source for collecting the exploits. You can consider some of the following protocols: i)TCP and UDP ii) ICMP iii) SMTP iv) HTTP v) SNMP vi) SSL vii) DNS viii) BGP (if you like to work on any other protocols, let me know) • The documentation should include the following: • -The effect of the exploit • -Reason for the exploit (hole in the spec., DOS, improper implementation, etc.,) • -Vendors effected • -Date when it was detected • (with a metric, how many places it was detected) • -What are the sequence of actions to arrive the exploit. Introduction: Part-1

7. Homework1 • Collect 25 exploits for each protocol (where ever it is applicable) • Search the IEEE database, web and books etc., and get the state diagram for the protocol. Make sure you relate the state diagram with the list of exploits. • Make sure you have conclusions • Relate the exploits with spec. See where and how it was broken; Is there any pattern ? Which vendor is more prone to these vulnerabilities ? Do you foresee any other holes will be exploited ? Introduction: Part-1

8. Project • Project Description (suggested) • Threat models and quantitative derivations for vulnerability. For example, you can start with a state diagram of the protocol and draw an attack graph. In this attack graph, you can use behavior attributes (or probabilistic, or any other methods) for traversing the graph and compute the vulnerability (using analytical methods). An example for BGP is given in the reference. The following protocols can be used for the analysis: RSVP, LDP, SIP, SCTP, and routing protocols. • Guidelines: Do not try to cut and past from documents. Creativity and innovation will be the only factors during evaluation of the project. Introduction: Part-1

9. Issues in Internet • QoS • Security • Availability Introduction: Part-1

10. millions of connected computing devices: hosts, end-systems pc’s workstations, servers PDA’s phones, toasters running network apps communication links fiber, copper, radio, satellite routers: forward packets (chunks) of data thru network router workstation server mobile local ISP regional ISP company network What’s the Internet: “nuts and bolts” view Introduction: Part-1

11. protocols: control sending, receiving of msgs e.g., TCP, IP, HTTP, FTP, PPP Internet: “network of networks” loosely hierarchical public Internet versus private intranet Internet standards RFC: Request for comments IETF: Internet Engineering Task Force What’s the Internet: “nuts and bolts” view router workstation server mobile local ISP regional ISP company network Introduction: Part-1

12. communication infrastructure enables distributed applications: WWW, email, games, e-commerce, database., voting, more? communication services provided: connectionless connection-oriented cyberspace [Gibson]: “a consensual hallucination experienced daily by billions of operators, in every nation, ...." What’s the Internet: a service view Introduction: Part-1

13. Perspective • Network users: Does the network support the users’ applications • Reliability • Error free service • Speed of data transfer • Network designers: Cost efficient network design • Good utilization of network resources • Cost of building the network • Types of services to be supported • Security Introduction: Part-1

14. Perspective • Network providers: Network administration and customer service • Maximize Revenue • Minimize Operations Expenses • Survivability and Resiliency (Why) • Discuss the difference! • Give examples Introduction: Part-1

15. network edge: applications and hosts network core: routers network of networks access networks, physical media: communication links A closer look at network structure: Introduction: Part-1

16. Building Blocks • Switches, Routers, Gateways • Special network components responsible for “moving” packets across the network from source to destination. • Network hosts, workstations, etc. • they generally represent the source and sink (destination) of data traffic (packets) • We can recursively build large networks by interconnecting networks via gateways and routers. Introduction: Part-1

17. An Interconnection Network Introduction: Part-1

18. end systems (hosts): run application programs e.g., WWW, email at “edge of network” client/server model client host requests, receives service from server e.g., WWW client (browser)/ server; email client/server peer-peer model: host interaction symmetric e.g.: teleconferencing The network edge: Introduction: Part-1

19. Goal: data transfer between end sys. handshaking: setup (prepare for) data transfer ahead of time Hello, hello back human protocol set up “state” in two communicating hosts TCP - Transmission Control Protocol Internet’s connection-oriented service TCP service[RFC 793] reliable, in-order byte-stream data transfer loss: acknowledgements and retransmissions flow control: sender won’t overwhelm receiver congestion control: senders “slow down sending rate” when network congested Network edge: connection-oriented service Introduction: Part-1

20. Goal: data transfer between end systems same as before! UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service unreliable data transfer no flow control no congestion control App’s using TCP: HTTP (WWW), FTP (file transfer), Telnet (remote login), SMTP (email) App’s using UDP: streaming media, teleconferencing, Internet telephony Network edge: connectionless service Introduction: Part-1

21. mesh of interconnected routers the fundamental question: how is data transferred through net? circuit switching: dedicated circuit per call: telephone net packet-switching: data sent thru net in discrete “chunks” The Network Core Introduction: Part-1

22. Different Types of Switching • Different Types of Switching: • Circuit Switching (telephone network) • dedicated circuit, sending and receiving bit streams • Message Switching • Packet Switching • store and forward, sending and receiving packets • Virtual Circuit Switching • Cell Switching (ATM) • What are Packets? • Data to be transmitted is divided into discrete blocks Introduction: Part-1

23. End-end resources reserved for “call” link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup required Network Core: Circuit Switching Introduction: Part-1

24. Cost-Effective Resource Sharing • Must share (multiplex) network resources among multiple users. • Common Multiplexing Strategies • Time-Division Multiplexing (TDM) • Synchronous TDM (STDM) • Frequency-Division Multiplexing (FDM) • Multiplexing multiple logical flows over a single physical link. Introduction: Part-1

25. network resources (e.g., bandwidth) divided into “pieces” pieces allocated to calls resource piece idle if not used by owning call (no sharing) dividing link bandwidth into “pieces” frequency division time division Network Core: Circuit Switching Introduction: Part-1

26. each end-end data stream divided into packets user A, B packets share network resources each packet uses full link bandwidth resources used as needed, Bandwidth division into “pieces” Dedicated allocation Resource reservation Network Core: Packet Switching resource contention: • aggregate resource demand can exceed amount available • congestion: packets queue, wait for link use • store and forward: packets move one hop at a time • transmit over link • wait turn at next link Introduction: Part-1

27. Packet-switching versus circuit switching: human restaurant analogy other human analogies? D E Network Core: Packet Switching 10 Mbs Ethernet C A statistical multiplexing 1.5 Mbs B queue of packets waiting for output link 45 Mbs Introduction: Part-1

28. Packet-switching: store and forward behavior Network Core: Packet Switching Introduction: Part-1

29. 1 Mbit link each user: 100Kbps when “active” active 10% of time circuit-switching: 10 users packet switching: with 35 users, probability > 10 active less that .004 Packet switching allows more users to use network! Packet switching versus circuit switching N users 1 Mbps link Introduction: Part-1

30. Great for bursty data resource sharing no call setup Excessive congestion: packet delay and loss protocols needed for reliable data transfer, congestion control Q: How to provide circuit-like behavior? bandwidth guarantees needed for audio/video apps still an unsolved problem (chapter 6) Is packet switching a “slam dunk winner?” Packet switching versus circuit switching Introduction: Part-1

31. Goal: move packets among routers from source to destination we’ll study several path selection algorithms (chapter 4) datagram network: destination address determines next hop routes may change during session analogy: driving, asking directions virtual circuit network: each packet carries tag (virtual circuit ID), tag determines next hop fixed path determined at call setup time, remains fixed thru call routers maintain per-call state Packet-switched networks: routing Introduction: Part-1

32. Q: How to connect end systems to edge router? residential access nets institutional access networks (school, company) mobile access networks Keep in mind: bandwidth (bits per second) of access network? shared or dedicated? Access networks and physical media Introduction: Part-1

33. Dialup via modem up to 56Kbps direct access to router (conceptually) ISDN: intergrated services digital network: 128Kbps all-digital connect to router ADSL: asymmetric digital subscriber line up to 1 Mbps home-to-router up to 8 Mbps router-to-home ADSL deployment: UPDATE THIS Residential access: point to point access Introduction: Part-1

34. HFC: hybrid fiber coax asymmetric: up to 10Mbps upstream, 1 Mbps downstream network of cable and fiber attaches homes to ISP router shared access to router among home issues: congestion, dimensioning deployment: available via cable companies, e.g., MediaOne Residential access: cable modems Introduction: Part-1

35. company/univ local area network (LAN) connects end system to edge router Ethernet: shared or dedicated cable connects end system and router 10 Mbs, 100Mbps, Gigabit Ethernet deployment: institutions, home LANs soon LANs: chapter 5 Institutional access: local area networks Introduction: Part-1

36. shared wireless access network connects end system to router wireless LANs: radio spectrum replaces wire e.g., Lucent Wavelan 10 Mbps wider-area wireless access CDPD: wireless access to ISP router via cellular network router base station mobile hosts Wireless access networks Introduction: Part-1

37. physical link: transmitted data bit propagates across link guided media: signals propagate in solid media: copper, fiber unguided media: signals propagate freelye.g., radio Twisted Pair (TP) two insulated copper wires Category 3: traditional phone wires, 10 Mbps ethernet Category 5 TP: 100Mbps ethernet Physical Media Introduction: Part-1

38. Coaxial cable: wire (signal carrier) within a wire (shield) baseband: single channel on cable broadband: multiple channel on cable bidirectional common use in 10Mbs Ethernet Physical Media: coax, fiber Fiber optic cable: • glass fiber carrying light pulses • high-speed operation: • 100Mbps Ethernet • high-speed point-to-point transmission (e.g., 5 Gps) • low error rate Introduction: Part-1

39. signal carried in electromagnetic spectrum no physical “wire” bidirectional propagation environment effects: reflection obstruction by objects interference Physical media: radio Radio link types: • microwave • e.g. up to 45 Mbps channels • LAN (e.g., waveLAN) • 2Mbps, 11Mbps • wide-area (e.g., cellular) • e.g. CDPD, 10’s Kbps • satellite • up to 50Mbps channel (or multiple smaller channels) • 270 Msec end-end delay • geosynchronous versus LEOS Introduction: Part-1

40. Different Types of Links Sometimes you install your own! Introduction: Part-1

41. Bigger Pipes! Sometimes leased from the phone company STS: Synchronous Transport Signal Introduction: Part-1

42. packets experience delay on end-to-end path four sources of delay at each hop nodal processing: check bit errors determine output link queueing time waiting at output link for transmission depends on congestion level of router transmission A propagation B nodal processing queueing Delay in packet-switched networks Introduction: Part-1

43. Transmission delay: R=link bandwidth (bps) L=packet length (bits) time to send bits into link = L/R Propagation delay: d = length of physical link s = propagation speed in medium (~2x108 m/sec) propagation delay = d/s transmission A propagation B nodal processing queueing Delay in packet-switched networks Note: s and R are very different quantitites! Introduction: Part-1

44. Performance Bandwidth (throughput) • Amount of data that can be transmitted per time unit • Example: 10Mbps • link versus end-to-end • Notation • KB = 210 bytes • Mbps = 106 bits per second Introduction: Part-1

45. Performance • Bandwidth related to “bit width” a) 1 second b) 1 second Introduction: Part-1

46. Latency (delay) • Time it takes to send message from point A to point B • Example: 24 milliseconds (ms) • Sometimes interested in in round-trip time (RTT) • Components of latency Latency = Propagation + Transmit + Queue + Proc. Propagation = Distance / SpeedOfLight Transmit = Size / Bandwidth Introduction: Part-1

47. The “hard” limit • Speed of light • 3.0 x 108 meters/second in a vacuum • 2.3 x 108 meters/second in a cable • 2.0 x 108 meters/second in a fiber • Notes • no queuing delays in direct link • bandwidth not relevant if Size = 1 bit • process-to-process latency includes software overhead • software overhead can dominate when Distance is small Introduction: Part-1

48. Relative importance of bandwidth and latency • small message (e.g., 1 byte): 1ms vs. 100ms dominates 1Mbps vs. 100Mbps • large message (e.g., 25 MB): 1Mbps vs. 100Mbps dominates 1ms vs. 100ms • Consider two channels of 1Mbps and 100 Mbps respectively. For a 1 byte message, the available bandwidth is relatively insignificant given a RTT of 1 ms. The transmit delay for each channel is 8 s and 0.08 s, respectively. Introduction: Part-1

49. Delay • Delay x Bandwidth Product e.g., 100ms RTT and 45Mbps Bandwidth = 560KB of data • We have to view the network as a buffer. This may have interesting consequences: • How much data did the sender transmit before a response can be received? Bandwidth Introduction: Part-1

50. Application Needs • bandwidth requirements: burst versus peak rate • jitter: variance in latency (inter-packet gap) • Average Bandwidth Requirement is Not enough: • consider a source with an avg. BW-requirement of 2Mbps. If the application generates 1 Mbit in one second interval and 3Mbit in a second, a channel that can support 2 Mbps max. will have a tough time. • Other Quality of Service (QOS) Parameters: • max. and min. delay • max. and min. bandwidth demand • rates for dynamic increase of demands • Cell-Loss Rate Introduction: Part-1