Introduction to Networking S Y STEMS

Transcription

1 Introduction to Networking CS 40: INTRODUCTION TO U NIX A ND L I NUX O P E R AT ING S Y STEMS

2 Objectives Introduce networking, including what it is and what it contains, which includes: Networking layers Protocols Addressing Subnets

3 There Is This Kind of Networking

4 And There Is Also This Kind of Networking

5 Then There Is This Kind of Networking

6 What Is Computer Networking? Connecting computers together so they can transfer data between each other Can connect one of two ways: Wired Wireless

7 Why Do We Network Computers? Print remotely Just like our printer in the back of the room Store data and applications on servers For example, saving files to the cloud The Internet! Browsing for information Connecting with others, whether by , social networking, or messaging

8 How Do We Model This Communication? Use a conceptual model Characterize and standardize the internal functions of the communication system Partition it into abstraction layers (i.e. don t worry about the implementation of the underneath layers right now) From this, what do we get?

9 Open Systems Interconnection (OSI) Model Application Presentation Session Transport Network Data Link Physical

10 OSI Model Physical Layer Defines the electrical and physical specifications of the data connection Provides the hardware the means of sending and receiving data on a carrier Examples: Ethernet, RJ45 Physical

11 OSI Model Data Link Layer Provides node-to-node data transfer, where data is encoded and decoded into bits Split into two layers Media Access Control (MAC) layer: responsible for controlling how devices in a network gain access to data and permission to transmit it Logical Link Control (LLC) layer: controls error checking and packet synchronization Data Link Physical Examples: Point-to-Point Protocol (PPP), Asynchronous Transfer Mode (ATM)

12 OSI Model Network Layer Provides the functional and procedural means of transferring variable length data sequences (called datagrams) from one node to another connected to the same network Translates logical network address physical address Network Data Link Physical Datagram delivery at this layer is not guaranteed to be reliable Examples: Internet Protocol (IP)

13 OSI Model Transport Layer Provides the functional and procedural means of transferring variable-length data sequences from a source to a destination host via one or more networks, while maintaining the quality of service functions Transport Network Data Link Physical Controls the reliability of a given link through flow control, segmentation, and error control (i.e. ensures complete data transfer) Examples: Transmission Control Protocol (TCP), User Datagram Protocol (UDP)

14 OSI Model Session Layer Session Transport Network Data Link Physical Controls the dialogues (connections) between computers Establishes, manages and terminates the connections between the local and remote application Provides for full-duplex, half-duplex, or simplex operation Simplex: two one-way streets Half-duplex: two-way street, only one flow of traffic allowed Full-duplex: two-way street, traffic allowed from both sides Examples: Network File System (NFS), Remote Procedure Calls (RPC)

15 OSI Model Presentation Layer Presentation Session Transport Network Provides independence from data representation (e.g., encryption) by translating between application and network formats Transforms data into the form that the application accepts Formats and encrypts data to be sent across a network Sometimes called the syntax layer Examples: ASCII, GIF, JPEG, MPEG Data Link Physical

16 OSI Model Application Layer Application Presentation Session Transport Closest to the end user Interacts with software applications that implement a communicating component Examples: World Wide Web (WWW), File Transfer Protocol (FTP) Network Data Link Physical

17 Protocols For communication, these are the rules for data exchange within or between computers In the Internet Protocol (IP), two of the major types of data transmission: Transmission Control Protocol (TCP) User Datagram Protocol (UDP)

18 User Datagram Protocol (UDP) Connectionless protocol i.e. data keeps being transmitted without knowing whether it got there or not Sometimes, the U is known as unreliable Works well to deal with lots of clients as data transfers quick and easy Examples: streaming media, online games, voice-over IP (VOIP)

19 Transmission Control Protocol (TCP) Reliable Connection between the two sides starts with synchronizing the connection and acknowledging both sides are ready for transmission Transmission of data is done with handshaking between the two sides Ordered Transmission of data is done with packets ordered sequentially Error-checked Duplicate packets can be thrown out with the sequence being kept

20 TCP Header

21 TCP Header Components TCP Header Field Description Number of Bits Source Port Number of the calling port 16 Destination Port Number of the called port 16 Sequence Number Number used to ensure correct sequencing of the arriving data Acknowledgment Number Next expected TCP octet 32 Header Length Number of 32-bit words in the header 4 Reserved Set to zero 6 32

22 TCP Header Components (2) TCP Header Field Description Number of Bits URG Indicates Urgent pointer field is significant 1 ACK PSH Indicates Acknowledgment field is significant; should be set after initial SYN packet Asks to push the buffered data to the receiving application RST Reset the connection 1 SYN Synchronize sequence numbers; only first packet from each end should have this set FIN No more data from sender

23 TCP Header Components (3) TCP Header Field Description Number of Bits Window Checksum Number of octets that the device is willing to accept Calculated checksum of the header and data fields Urgent Indicates the end of the urgent data 16 Options Examples: maximum window size, window scaling Data Data to be transmitted Varies

24 Addressing A way to identify a computer uniquely on a network Ways to think about it: Home or work address Driver s License El Camino College ID # How do we do this physically?

25 Physical Address: MAC Each network interface has a Media Access Control (MAC) address This 6-byte address is burned into each device Each identifier is unique (1 of 2 48 possibilities) Example MAC address: 01:23:45:67:89:ab But, how do we map ourselves logically on the information superhighway?

26 Logical Address: IP Numerical label assigned to each device participating in a computer network that uses the Internet Protocol (IP) for communication Devices include: Computers Printers Smart phones Example IP address:

27 Addressing Used to Deliver Data Network Access Layer Addresses Internet Layer Addresses Transport Layer Addresses Destination MAC Address Source MAC Address Destination IP Address Source IP Address Destination Port Source Port Application Data

28 Internet Address Classes Three types of Internet address classes Class A Class B Class C Today, we will be looking at IP v4 addressing There is now IP v6 addressing, with the difference being the increase in bits for addresses from 32 bits (4 bytes) to 128 bits (16 bytes)

29 Class A Internet Address Network (1 126) Host Host Host First byte is the network address Final 3 bytes are the host address 126 Class A networks, each with up to 16,777,216 hosts On the Internet, all Class A networks have been assigned

30 Class B Internet Address Network ( ) Network Host Host First 2 bytes are the network address Final 2 bytes are the host address 16,384 Class B networks, each with up to 65,536 addresses

31 Class C Internet Address Network ( ) Network Network Host First 3 bytes are the network address Final byte is the host address 2,097,152 Class C networks, each with up to 256 hosts

32 Reserved Addresses According to Request for Comments, which does the principal technical development and standard settings for the Internet, with RFC 1918, the following addresses are reserved: Used as internal private addresses Do not connect directly to the public Internet

33 Before We Start Talking Calculations We need to understand our binary representation, with its decimal conversion Bit Binary Decimal Decimal Sum The decimal row is 2 bit (e.g. 2 7 = 128, 2 3 = 8) The decimal sum row is adding the bits from 7 0 together (e.g = = 224, = = 248)

34 Calculating Address Space Write the 32-bit host address in binary notation Host

35 Calculating Address Space (2) Write the 32-bit subnet mask in binary notation Host Mask

36 Calculating Address Space (3) Draw a vertical line just after the last contiguous subnet mask 1 bit Host Mask

37 Calculating Address Space (4) In a row below, copy the host address line Then, place 0 s to the right of the line in all the remaining free spaces This will be the subnet Host Mask Subnet

38 Calculating Address Space (5) In a row below, copy the host address line Then, place 1 s to the right of the line in all the remaining free spaces This will be the broadcast address Host Mask Subnet Broadcast

39 Calculating Address Space (6) In a row below, copy the subnet address line Then, replace the last 0 with a 1 This will be the first usable address Host Mask Subnet Broadcast First

40 Calculating Address Space (7) Step 4: In a row below, copy the broadcast address line Then, replace the last 1 with a 0 This will be the last usable address Host Mask Subnet Broadcast First Last

41 Calculating a Subnet Mask How do we know what subnet mask to use? It ll depend on how we balance the following: Number of hosts Number of sub-networks

42 Calculating a Subnet Mask Example Let s say I have a network I want to subnet it to support all my networks and hosts I expect to have 100 remote sites to support Each of these remote sites supports 300 computers What subnet mask do I need?

43 Calculating a Subnet Mask Example (2) First, let s look at the minimal subnet mask for this network If you have a network, you need a subnet to cover the portion Let s get the binary representation of : Network

44 Calculating a Subnet Mask Example (3) Now, we need to have a subnet mask that, when you or the bits, will capture the network Let s take a simple one such as : Network Mask The good news: it ll support 65,536 hosts The bad news: it ll support just 1 network

45 Calculating a Subnet Mask Example (4) What do we do? Add 1 s to the subnet mask to add networks Let s try adding 5 1 s to the subnet mask: Network Mask Adding 5 1 s means adding 2 n 2 = networks or 30 networks, still not quite enough to meet 100 networks

46 Calculating a Subnet Mask Example (5) Let s try adding 2 more 1 s to the subnet mask and make it 7: Network Mask Adding 7 1 s means adding networks or 126 networks, just enough to meet 100 networks

47 Calculating a Subnet Mask Example (6) How about calculating the number of hosts? Network Mask Count the number of 0 s from the right until we hit the first 1; in our case, 9 Then use the formula 2 n 2 to get the number of hosts From this, we get hosts = = 510 hosts > 300 hosts GOOD TO GO!

48 Class B Addressing Let s look at the private network Host We ll use the same subnet mask from our last example: Host Mask Remember, we have 126 (2 7 2) networks and 510 (2 9 2) hosts per network

49 Class B Addressing (2) Now, let s create our first subnet: Network Mask Subnet

50 Class B Addressing (3) From here, we can create our first and last addresses for this subnet, as well as the broadcast address: Network Mask Subnet First Last Broadcast

51 Class B Addressing (4) Now, let s create our second subnet: Network Mask Subnet

52 Class B Addressing (5) From here, we can create our first and last addresses for this subnet, as well as the broadcast address: Network Mask Subnet First Last Broadcast

53 Class B Addressing (6) Number of Bits Subnet Mask Number of Subnets Number of Hosts

54 Class B Addressing (6) Number of Bits Subnet Mask Number of Subnets Number of Hosts

55 Class C Addressing Let s look at the network Network We ll use a different subnet mask this time: Network Mask Here, we have 6 (2 3 2) networks and 30 (2 5 2) hosts per network

56 Class C Addressing (2) Now, let s create our first subnet: Network Mask Subnet

57 Class C Addressing (3) From here, we can create our first and last addresses for this subnet, as well as the broadcast address: Network Mask Subnet First Last Broadcast

58 Class C Addressing (4) Now, let s create our second subnet: Network Mask Subnet

59 Class C Addressing (5) From here, we can create our first and last addresses for this subnet, as well as the broadcast address: Network Mask Subnet First Last Broadcast

60 Class C Addressing (6) Number of Bits Subnet Mask Number of Subnets Number of Hosts