1. Data Networking Overview Presented by Scott M. Ballew Copyright of Scott M. Ballew and Purdue University, July 19, 2007

2. 2 Agenda  Network Models  Network Technologies Layer 1 Layer 2 Etc.  Network Security  Network Usability The Domain Name System Host Configuration Remote Access

3. 3 Network Models  Network models use layers to describe networks  Each layer describes the services provided to the layer above it and those required from the layer below it  It also describes the format of exchanges between peer layers on different network hosts  Because the layers “stack” on top of one another, we often refer to network protocol “stacks” when we talk about the implementation Layer N Layer N+1 Layer N-1 Layer N+1 Layer N Layer N-1 Provides Requires Exchanges

4. 4 Network Models  The most well-known network model is the OSI (Open Systems Interconnect) Reference Model defined and maintained by the Organization for International Standardization (ISO)  It consists of seven layers, numbered from the bottom (closest the network) to the top (closest the user) Layer 1 – Physical Layer 2 – Data Link Layer 3 – Network Layer 4 – Transport Layer 5 – Session Layer 6 – Presentation Layer 7 – Application

5. 5 OSI Reference Model  Layer 1 – The Physical Layer Defines the type of media to be used Defines representation of data on the medium »Is a ‘0’ “high” or “low”, “on” or “off”? »What order are bits transmitted (if serial)? Layer 1 – Physical

6. 6 OSI Reference Model  Layer 2 – The Data Link Layer Defines “right to transmit” rules Provides directly- connected host-to-host data transfer Defines higher-level structure of data (frames) Defines “physical” address structure for hosts Layer 1 – Physical Layer 2 – Data Link

7. 7 OSI Reference Model  Layer 3 – The Network Layer Provides end-host-to- end-host data transfer across (potentially) multiple data links Defines higher-level structure of data (packets) Defines “abstract” address structure for hosts Layer 1 – Physical Layer 2 – Data Link Layer 3 – Network

8. 8 OSI Reference Model  Layer 4 – The Transport Layer Provides process-to- process data transfer May provide for reliable data transfer Defines higher-level structure for data (datagrams, streams, etc.) Defines “port” addresses for services (processes) Layer 1 – Physical Layer 2 – Data Link Layer 3 – Network Layer 4 – Transport

9. 9 OSI Reference Model  Layer 5 – The Session Layer Provides a logically persistent connection between processes May involve user or host authentication (login), transaction encapsulation (for database access), etc. Layer 1 – Physical Layer 2 – Data Link Layer 3 – Network Layer 4 – Transport Layer 5 – Session

10. 10 OSI Reference Model  Layer 6 – The Presentation Layer Defines the network representation of data Converts between the network and host representations of data (ASCII/EBCDIC, byte order, encryption, compression, etc.) Layer 1 – Physical Layer 2 – Data Link Layer 3 – Network Layer 4 – Transport Layer 5 – Session Layer 6 – Presentation

11. 11 OSI Reference Model  Layer 7 – The Application Layer Provides a portal for the application to access the network Describes the dialog between two applications communicating across the network. Layer 1 – Physical Layer 2 – Data Link Layer 3 – Network Layer 4 – Transport Layer 5 – Session Layer 6 – Presentation Layer 7 – Application

12. 12 TCP/IP Network  When TCP/IP was defined in the early days of the Internet, the OSI Reference Model had not been defined, so a different layering model was used  It consists of 4 or 5 layers, and maps closely to the OSI Reference Model Layer 1 – Physical Layer 2 – Link Layer 3 – Internetwork Layer 4 – Transport Layer 5 – Application

13. 13 TCP/IP Network  Layers 1 & 2 – The Physical and Link Layers Provide physical communications between hosts within a network. Sometimes combined into a single “Link” layer. Correspond to OSI layers 1 and 2 Layer 1 – Physical Layer 2 – Link

14. 14 TCP/IP Network  Layer 3 – The Internetwork Layer Provides all necessary components to move data between networks, including addressing, routing, etc. Corresponds to OSI layer 3 Layer 1 – Physical Layer 2 – Link Layer 3 – Internetwork

15. 15 TCP/IP Network  Layer 4 – The Transport Layer Provides everything necessary to move data between applications Corresponds to OSI layer 4 Layer 1 – Physical Layer 2 – Link Layer 3 – Internetwork Layer 4 – Transport

16. 16 TCP/IP Network  Layer 5 – The Application Layer Provides everything specific to an application or a session Corresponds to OSI layers 5 through 7 Layer 1 – Physical Layer 2 – Link Layer 3 – Internetwork Layer 4 – Transport Layer 5 – Application

17. 17 Agenda  Network Models  Network Technologies Layer 1 Layer 2 Etc.  Network Security  Network Usability The Domain Name System Host Configuration Remote Access

18. 18 Network Technologies – L1  Layer 1 – The Physical Layer Copper Cable »Coax – bulky, heavy, but relatively immune to noise »Twisted pair – thinner, lighter, cheaper, and okay about noise Fiber Optic Cable »Multi-mode – good for relatively short distances (a couple of km) and moderate speeds (< 10 Gbps) »Single-mode – good for short and long distances (100+ km) and virtually any speed Radio, Microwaves, Satellite, others  None are inherently secure!

19. 19 Network Technologies – L2  Layer 2 – The Data Link Layer Ethernet Token Ring FDDI ATM SLIP/PPP Frame Relay SONET Waxed String

20. 20 Network Technologies – L2  Ethernet Ethernet has a very simple transmission control protocol 1.Listen to the network 2.If someone is talking, wait your turn 3.If no one is talking, send your data 4.If someone starts talking while you are talking, stop talking and scream at them!

21. 21 Network Technologies – L2  Ethernet transmissions occur in “frames” of 64 to 1518 octets in length  The frame contains a header, data, and a checksum  The header contains source and destination addresses and the frame type 64 – 1518 octets Header Data FCSFCS Dst AddressSrc AddressType 6 octets 2 4 octets 14 octets

22. 22 Network Technologies – L2  Early Ethernet devices had fairly basic functions Transceivers physically connect hosts to the Ethernet coax cable Repeaters amplify and repeat frames from one coax cable to another Bridges selectively amplify and repeat frames from one coax cable to another

23. 23 Network Technologies – L2  Hubs provide a combination of convenience and flexibility Coax hubs were a way to share a transceiver among multiple systems to avoid having to install so many. They used the same cable between a system and the hub as was used between a system and a transceiver Twisted pair Ethernet hubs made it practical to provide network connections in office spaces  Hub == Repeater!

24. 24 Network Technologies – L2  Switches provide for improved performance Recall that bridges selectively forward frames from one network segment to another, while repeaters (hubs) always forward frames from one network segment to another Switches are simply multi-port bridges implemented in hardware

25. 25 Network Technologies – L2  Finally, Wireless Access Points removed the need for cables between the network and the system An access point is sort of a hub/switch hybrid »Individual systems have to share available bandwidth (radio waves) »Frames are selectively transmitted between network segments (wired/wireless) »Wireless systems may or may not be able to “hear” each other’s transmissions

26. 26 Network Technologies – L3  Layer 3 – The Network Layer Layer 3 is where we connect layer 2 networks together The layer 2 networks can be the same or different technologies They can be the same or different speeds Many of the concepts are the same as layer 2, only different

27. 27 Network Technologies – L3  IPv4 is the most successful layer 3 protocol ever developed Hundreds of millions of systems Every time zone Every continent (yes, even Antarctica!)  The basic protocol is unchanged since its inception in the early 80’s

28. 28 Header Payload TTL Source Address Destination Address Identification VER Options Total Length Header Checksum TOS Protocol IHL Padding Offset Flags Network Technologies – L3  IP Packets Header »Addresses »Protocol »Control information Payload (data) 32 bits

29. 29  IP Addresses Network Technologies – L3... 172 10101100 24 00011000 57 00111001 18 00010010

30. 30 Network Technologies – L3  All systems on a single layer 2 network must have IP addresses with the same prefix  This prefix is the network portion of the IP address – the remainder is the host portion  IP addresses are arbitrarily split into a network portion and a host portion – local network administrators decide where the split between the network and host portions is rather than the protocol

31. 31 Network Technologies – L3  Network Masks Network masks specify where the split between network and host portions is A mask is a 32-bit quantity, just like an IP address, and can be represented the same way as a dotted “quad”... 255 11111111 255 11111111 255 11111111 0 00000000

32. 32 Network Technologies – L3  Network Masks (cont) 10101100 00011000 00111001 00010010 11111111 11111111 11111111 00000000 10101100 00011000 00111001 00000000 172.24.57.18 255.255.255.0 172.24.57.0 10101100 00011000 00111001 00010010 11111111 11111111 11111111 11110000 10101100 00011000 00111001 00010000 172.24.57.18 255.255.255.240 172.24.57.16

33. 33 Network Technologies – L3  Network Masks (cont.) Knowing the network mask is important to understanding the structure of any IP address. But writing “172.24.57.18 with mask 255.255.255.0” is cumbersome. We could shorten it to “172.24.57.18/255.255.255.0”, but even that is longer than we need.

34. 34 Network Technologies – L3  Slash Notation 11111111 11111111 11111111 00000000 255.255.255.0 11111111 11111111 11111111 11110000 255.255.255.240 24 bits 28 bits 172.24.57.18/255.255.255.0 172.24.57.18/255.255.255.240 172.24.57.18/24 172.24.57.18/28

35. 35 Network Technologies – L3  Routers are the primary Layer 3 device  Routers perform two distinct functions: Switch packets between networks Maintain network topology information

36. 36 Network Technologies – L3  “Layer-3 switches” is a newer term It may just be another term for “router” (i.e. a marketing term) May be a “hybrid” L2/L3 device »Grew “up” from L2 »Grew “down” from L3

37. 37 Network Technologies – L3  Basic IP Routing (Switching) Algorithm Look at the destination IP address »If it is one of my addresses, deliver it to the local system »Else if it is on one of my attached networks, deliver it directly using link-specific mechanisms »Else find the longest match (address/mask) in a local table and send the packet to the next hop address from that entry »Else inform the sender of failure

38. 38 Network Technologies – L3  Routing Tables Mandatory Information »Destination IP Address »Netmask »Next Hop Router Address Optional Information »Layer 2 information (address) »Interface index »Flags

39. 39 Network Technologies – L3  Routing Table Maintenance Static Configuration »Works well for small tables with little need for change Dynamic Routing Protocols »Allows routers (and sometimes hosts) to inform each other about current network topology »Work well for large tables or highly dynamic networks, but are often overkill for hosts

40. 40 Network Technologies – L3  Routing Protocols Many variations Some designed for use within a site network (Interior Gateway Protocols) Some designed for use between sites (Exterior Gateway Protocols) All have the same goal – a consistent view of the network topology!

41. 41 Network Technologies – L3  Other Network Protocols AppleTalk IPX (Novell Netware) DECNet

42. 42 Network Technologies – L4  Layer 4 – The Transport Layer Allow multiple processes/programs to use the IP network on same host Additionally, layer 4 may provide for reliable communications between these processes The IP protocol suite defines two major layer 4 protocols – UDP and TCP

43. 43 Network Technologies – L4  UDP – The User Datagram Protocol Connectionless Datagram based Unreliable “Quick & Dirty”  Common uses: Domain Name System (DNS) Simple Network Management Protocol (SNMP) Older Network File System (NFS)

44. 44 Network Technologies – L4  TCP – The Transmission Control Protocol Connection-oriented Stream based Reliable »In order »Once and only once “Heavy weight” »3-way handshake  Common uses: Remote login (Telnet, RSH/Rlogin, SSH) File Transfer (FTP, SCP, HTTP) Newer NFS

45. 45 Network Technologies – L4  There are other Layer 4 protocols in the IP family  Most try to combine features of UDP and TCP Example: A reliable datagram protocol

46. 46 Network Technologies – L5+  Layer 5+ - The Session, Presentation, and Application Layers Telnet – Remote Login File Transfer Protocol (FTP) – File Transfer Simple Mail Transfer Protocol (SMTP) – Email RSH/Rlogin – Remote Login HyperText Transfer Protocol (HTTP) – World Wide Web SSH/SCP – Secure Remote Login/File Transfer Many others!

47. 47 Agenda  Network Models  Network Technologies Layer 1 Layer 2 Etc.  Network Security  Network Usability The Domain Name System Host Configuration Remote Access

48. 48 Network Security  Security Devices Firewalls »Packet Filters »Stateless or Stateful »Network or Host-based Intrusion Detection/Prevention Systems (IDS/IPS) »Network or Host-based

49. 49 Network Security  Security Protocols Ident SSH – Secure Shell SSL – Secure Sockets Layer IPSec

50. 50 Agenda  Network Models  Network Technologies Layer 1 Layer 2 Etc.  Network Security  Network Usability The Domain Name System Host Configuration Remote Access

51. 51 Network Usability  The Domain Name System (DNS) Provides Name-to-Address mapping Also provides Address-to-Name mapping Implemented as a distributed database of trusting systems DO NOT trust the DNS blindly! »Subject to attacks »Not all DNS servers are controlled by “good” people

52. 52 Network Usability  Host Configuration Need 4 critical items »Own IP address »Network mask »Routing Table »DNS Servers’ IP addresses Dynamic Host Configuration Protocol (DHCP)

53. 53 Network Usability  Remote Access Modems Virtual Private Networks (VPN) »Point-to-Point Tunneling Protocol (PPTP) »IPSec »SSL

54. 54 Television is an invention which allows people to entertain you in your living room that you would never allow in your house. -David Frost The Internet is an invention which allows people to access your computer that you would never allow in your house.