1. 1 Introduction to Networking Concepts Chu-Sing Yang Department of Electrical Engineering National Cheng Kung University

2. 2 Networking Concepts Network Definition Protocol Architecture Protocol Layers Encapsulation/Decapsulation Network Abstractions Internet Control Message Protocol (ICMP)

3. Network Definitions A network can be defined as two or more computers connected together in such a way that they can share resources. The purpose of a network is to share resources. –A file –A folder –A printer –A disk drive –Or just about anything else that exists on a computer.

4. Network Definitions(cont..) A network is simply a collection of computers or other hardware devices that are connected together, either physically or logically, using special hardware and software, to allow them to exchange information and cooperate. Networking is the term that describes the processes involved in designing, implementing, upgrading, managing and otherwise working with networks and network technologies.

5. Advantages of Networking Connectivity and Communication Data Sharing Hardware Sharing Internet Access Internet Access Sharing Data Security and Management Performance Enhancement and Balancing Entertainment

6. The Disadvantages of Networking Network Hardware, Software and Setup Costs Hardware and Software Management and Administration Costs Undesirable Sharing Illegal or Undesirable Behavior Data Security Concerns

7. Fundamental Network Classifications Local Area Networks (LANs): A local area network (LAN) is a computer network covering a small geographic area, like a home, office, or group of buildings Wide Area Networks (WANs): Wide Area Network (WAN) is a computer network that covers a broad area (i.e., any network whose communications links cross metropolitan, regional, or national boundaries). Or, less formally, a network that uses routers and public communications links The largest and most well-known example of a WAN is the Internet. WANs are used to connect LANs and other types of networks together, so that users and computers in one location can communicate with users and computers in other locations Metropolitan Area Network (MAN): o A metropolitan area network (MAN) is a network that interconnects users with computer resources in a geographic area or region larger than that covered by even a large local area network (LAN) but smaller than the area covered by a wide area network (WAN). The term is applied to the interconnection of networks in a city into a single larger network (which may then also offer efficient connection to a wide area network). It is also used to mean the interconnection of several local area networks by bridging them with backbone lines. The latter usage is also sometimes referred to as a campus network.

8. 8 Sending a packet from Argon to Neon

9. 9 DNS: The IP address of “neon.tcpip-lab.edu ” is 128.143.71.21 ARP: What is the MAC address of 128.143.137.1? Sending a packet from Argon to Neon DNS: What is the IP address of “neon.tcpip-lab.edu ” ? ARP: The MAC address of 128.143.137.1 is 00:e0:f9:23:a8:20 128.143.71.21 is not on my local network. Therefore, I need to send the packet to my default gateway with address 128.143.137.1 frame 128.143.71.21 is on my local network. Therefore, I can send the packet directly. ARP: The MAC address of 128.143.137.1 is 00:20:af:03:98:28 ARP: What is the MAC address of 128.143.71.21? frame

10. 10 Communications Architecture The complexity of the communication task is reduced by using multiple protocol layers: Each protocol is implemented independently Each protocol is responsible for a specific subtask Protocols are grouped in a hierarchy A structured set of protocols is called a communications architecture or protocol suite

11. 11 TCP/IP Protocol Suite The TCP/IP protocol suite is the protocol architecture of the Internet The TCP/IP suite has four layers: Application, Transport, Network, and Data Link Layer End systems (hosts) implement all four layers. Gateways (Routers) only have the bottom two layers.

12. 12 Functions of the Layers Data Link Layer: –Service: Reliable transfer of frames over a link Media Access Control on a LAN –Functions: Framing, media access control, error checking Network Layer: –Service: Move packets from source host to destination host –Functions: Routing, addressing Transport Layer: –Service: Delivery of data between hosts –Functions: Connection establishment/termination, error control, flow control Application Layer: –Service: Application specific (delivery of email, retrieval of HTML documents, reliable transfer of file) –Functions: Application specific

13. 13 TCP/IP Suite and OSI Reference Model The TCP/IP protocol stack does not define the lower layers of a complete protocol stack

14. 14 Assignment of Protocols to Layers

15. 15 Layered Communications An entity of a particular layer can only communicate with: 1. a peer layer entity using a common protocol (Peer Protocol) 2. adjacent layers to provide services and to receive services

16. 16 Layered Communications A layer N+1 entity sees the lower layers only as a service provider Service Provider N+1 Layer Entity N+1 Layer Peer Protocol Request Delivery Indicate Delivery

17. 17 Service Access Points A service user accesses services of the service provider at Service Access Points (SAPs) A SAP has an address that uniquely identifies where the service can be accessed

18. 18 Exchange of Data The unit of data send between peer entities is called a Protocol Data Unit (PDU) For now, let us think of a PDU as a single packet Scenario: Layer-N at A sends a layer-N PDU to layer-N at B What actually happens: –A’s layer-N passes the PDU to one the SAPs at layer-N-1 –Layer-N-1 entity at A constructs its own (layer-N-1) PDU which it sends to the layer-N-1 entity at B –PDU at layer-N-1 = layer-N-1 Header + layer –N PDU AB

19. 19 Exchange of Data AB

20. 20 Layers in the Example

21. 21 Layers in the Example Send HTTP Request to neon Establish a connection to 128.143.71.21 at port 80 Open TCP connection to 128.143.71.21 port 80 Send a datagram (which contains a connection request) to 128.143.71.21 Send IP datagram to 128.143.71.21 Send the datagram to 128.143.137.1 Send Ethernet frame to 00:e0:f9:23:a8:20 Send Ethernet frame to 00:20:af:03:98:28 Send IP data-gram to 128.143.71.21 Send the datagram to 128.143.7.21 Frame is an IP datagram IP datagram is a TCP segment for port 80

22. 22 Layers and Services Service provided by TCP to HTTP: –reliable transmission of data over a logical connection Service provided by IP to TCP: –unreliable transmission of IP datagrams across an IP network Service provided by Ethernet to IP: –transmission of a frame across an Ethernet segment Other services: –DNS: translation between domain names and IP addresses –ARP: Translation between IP addresses and MAC addresses

23. 23 Encapsulation and Demultiplexing As data is moving down the protocol stack, each protocol is adding layer-specific control information

24. 24 Encapsulation and Demultiplexing in our Example Let us look in detail at the Ethernet frame between Argon and the Router, which contains the TCP connection request to Neon. This is the frame in hexadecimal notation. 00e0 f923 a820 00a0 2471 e444 0800 4500 002c 9d08 4000 8006 8bff 808f 8990 808f 4715 065b 0050 0009 465b 0000 0000 6002 2000 598e 0000 0204 05b4

25. 25 Parsing the information in the frame

26. 26 Encapsulation and Demultiplexing

27. 27 Encapsulation and Demultiplexing: Ethernet Header

28. 28 Encapsulation and Demultiplexing: IP Header

29. 29 Encapsulation and Demultiplexing: IP Header

30. 30 Encapsulation and Demultiplexing: TCP Header Option: maximum segment size

31. 31 Encapsulation and Demultiplexing: TCP Header

32. 32 Encapsulation and Demultiplexing: Application data No Application Data in this frame

33. 33 Different Views of Networking Different Layers of the protocol stack have a different view of the network. This is HTTP’s and TCP’s view of the network.

34. 34 Network View of IP Protocol

35. 35 Network View of Ethernet Ethernet’s view of the network

36. 36 Internet Control Message Protocol (ICMP)

37. 37 The IP (Internet Protocol) relies on several other protocols to perform necessary control and routing functions: Control functions (ICMP) Multicast signaling (IGMP) Setting up routing tables (RIP, OSPF, BGP, PIM, …) Overview

38. 38 Overview The Internet Control Message Protocol (ICMP) is a helper protocol that supports IP with facility for –Error reporting –Simple queries ICMP messages are encapsulated as IP datagrams:

39. 39 ICMP Message Format 4 byte header: Type (1 byte): type of ICMP message Code (1 byte): subtype of ICMP message Checksum (2 bytes): similar to IP header checksum. Checksum is calculated over entire ICMP message If there is no additional data, there are 4 bytes set to zero.  each ICMP messages is at least 8 bytes long

40. 40 ICMP Query Message ICMP query: Request sent by host to a router or host Reply sent back to querying host

41. 41 Example of ICMP Queries Type/Code: Description 8/0 Echo Request 0/0 Echo Reply 13/0 Timestamp Request 14/0Timestamp Reply 10/0 Router Solicitation 9/0Router Advertisement The ping command uses Echo Request/ Echo Reply

42. 42 Ping’s are handled directly by the kernel Each Ping is translated into an ICMP Echo Request The Ping’ed host responds with an ICMP Echo Reply Example of a Query: Echo Request and Reply Host or Router ICMP ECHO REQUEST Host or router ICMP ECHO REPLY

43. 43 Example of a Query: ICMP Timestamp A system (host or router) asks another system for the current time. Time is measured in milliseconds after midnight UTC (Universal Coordinated Time) of the current day Sender sends a request, receiver responds with reply Sender Receiver Timestamp Request Timestamp Reply

44. 44 ICMP Error message ICMP error messages report error conditions Typically sent when a datagram is discarded Error message is often passed from ICMP to the application program

45. 45 ICMP Error message ICMP error messages include the complete IP header and the first 8 bytes of the payload (typically: UDP, TCP)

46. 46 Frequent ICMP Error message TypeCodeDescription 30–15Destination unreachable Notification that an IP datagram could not be forwarded and was dropped. The code field contains an explanation. 50–3RedirectInforms about an alternative route for the datagram and should result in a routing table update. The code field explains the reason for the route change. 110, 1Time exceeded Sent when the TTL field has reached zero (Code 0) or when there is a timeout for the reassembly of segments (Code 1) 120, 1Parameter problem Sent when the IP header is invalid (Code 0) or when an IP header option is missing (Code 1)

47. 47 Some subtypes of the “Destination Unreachable” Code Description Reason for Sending 0Network Unreachable No routing table entry is available for the destination network. 1Host Unreachable Destination host should be directly reachable, but does not respond to ARP Requests. 2Protocol Unreachable The protocol in the protocol field of the IP header is not supported at the destination. 3Port Unreachable The transport protocol at the destination host cannot pass the datagram to an application. 4Fragmentation Needed and DF Bit Set IP datagram must be fragmented, but the DF bit in the IP header is set.

48. 48 Example: ICMP Port Unreachable RFC 792: If, in the destination host, the IP module cannot deliver the datagram because the indicated protocol module or process port is not active, the destination host may send a destination unreachable message to the source host. Scenario: Client Request a service at a port 80 Server No process is waiting at port 80 Port Unreachable