01/17/08 TDC /17/08 TDC363-03

Transcription

1 Introduction to LAN TDC 363 Week 3 Network Protocols Book: Chapter 4 & 11 1 Outline The TCP/IP model vs. the OSI Model IP Address Address Resolution Protocol (ARP) IPX/SPX and NetBIOS Protocols on Windows XP DNS and WINS TCP and UDP NAT and Firewall BOOTP and DHCP TCP/IP utilities on Windows 2000/XP Application Layer Protocols 2 Introduction to Protocols Protocol Rules network uses to transfer data Protocols that can span more than one LAN segment are routable Multiprotocol network Network using more than one protocol 3

2 TCP/IP and OSI model 4 IP (Internet Protocol) Provides information about how and where data should be delivered Data s source and destination addresses Network layer protocol Enables TCP/IP to internetwork Unreliable, connectionless protocol IP datagram: packet, in context of TCP/IP Envelope for data 5 IP (continued) 6

3 IP Addressing IP Address Logical address used in TCP/IP networking Unique 32-bit number Divided into four groups of octets (8 (8-bit bitbytes)thatare bytes) that are separated by periods E.g., ( 7 IP Addressing Though 8 bits have 256 possible combinations, only the numbers 1 through 254 are used to identify networks and hosts Numbers 0 is reserved for network and 255 is reserved for broadcast Broadcast is transmissions to all stations on a network Total: 2 32 = 4,294,967,296 8 IP Addressing Loopback address IP address reserved for communicating from a node to itself (localhost) Value of the loopback address is always Internet Corporation for Assigned Names and Numbers (ICANN) Non-profit organization to maintain and assign IP addresses 9

4 Internet Name and Address ICANN Internet Corporation for Assigned Names and Numbers Address SO Domain Name SO Protocol SO Regional Internet Registries ARIN APNIC RIPE-NCC 10 Why IP Addresses? Unique addressing allows communication between end stations Unicast (one-to to-one) one) Broadcast (one-to to-all) Multicast (one-to to-many) Path choice is based on location Location is represented by an address 11 IP Addressing Scheme Dotted Decimal Network 32 bits Host Maximum network host 12

5 IP addresses and Classes 13 IP Address Problem and Solutions Total: 2 32 = 4,294,967,296 Only 2M Class C networks Classless Inter-Domain Routing (CIDR) RFC 1519 IP Subnet Mask Network Address Translation (NAT) RFC 1631 Use of private IP addresses behind the router IPv4 vs. IPv6 14 IP Address CIDR Subnet Mask Network Subnet Host The broadcast and routing is based on the IP subnet mask. With CIDR, Class, A, B, and C networks lose its significance, and only the IP subnet mask is significant to determine the routing and broadcasting. CIDR is covered in details in TDC365. For TDC363, I will try to stay in Class C with subnet mask =

6 IP Routing Table / /24 E0 E PC1 PC Network Address Interface /24 E /24 E1 /24: IP Routing Table E / / /24 E1 E4 E / /24 E /24 Network Address Interne t Interface /24 E /24 E /24 E /24 E /0 E /0 default 17 Frame/Packet Trace / aa.bb.cc Gateway (router) / aa.bb.cd aa.bb.cc PC1 PC aa.bb.cd Frame/Packet Address Info: MAC DA: aa.bb.cc MAC SA: aa.bb.cc IP DA: IP SA: Frame/Packet Address Info MAC DA: aa.bb.cd MAC SA: aa.bb.cd IP DA: IP SA:

7 Routing Protocols Revisited Static Routing Manually populate the routing table the route command The four most common routing gp protocols: RIP (Routing Information Protocol) for IP and IPX OSPF (Open Shortest Path First) for IP EIGRP (Enhanced Interior Gateway Routing Protocol) for IP, IPX, and AppleTalk BGP (Border Gateway Protocol) for IP 19 Address Resolution Protocol (ARP) ARP table Layer 2 to layer 3 mapping Database that lists the associated MAC and IP addresses Contains two types of entries: Dynamic ARP table entries Static ARP table entries ARP utility provides a way of obtaining information from and manipulating a device s ARP table 20 How does ARP work? :88:77:11:11: :88:77:22:22: :88:77:33:33:33 1. Who is ? 2a.. It is not me. 2b. It is me. 4. OK. Let us create an ARP entry :88:77:33:33:33 3. My MAC address is 99:88:77:33:33:33. 21

8 ARP Table :88:77:11:11: :88:77:22:22: :88:77:33:33: :88:77:22:22: :88:77:33:33: :88:77:11:11: :88:77:22:22: :88:77:11:11: :88:77:33:33:33 22 Questions you will see at Midterm MAC forwarding table: layer 1 to layer 2 mapping ARP Table: layer 2 to layer 3 mapping Routing Table: layer 1 to layer 3 mapping Packet and Frame trace Source MAC address Destination MAC address Source IP address Destination IP address 23 Host Names and Domain Name System (DNS) Host name Symbolic name that describes a TCP/IP device Domain Group of computers that belong to the same organization and have part of their IP addresses in common Note: Domain Name in TCP/IP is different from Domain Name in Windows. 24

9 Addresses and Names In addition to using IP addresses, TCP/IP networks use names for networks and hosts Each host requires a host name /etc/hosts, %windows%\system32\drivers\etc\hosts Each network requires a network name, also called a domain name cti.depaul.edu or depaul.edu Together, host name and domain name constitute the fully qualified domain name (FQDN) facweb.cti.depaul.edu 25 Domain Names Symbolic name that identifies an organization Top-level domains (TLDs) Highest-level category used to distinguish domain names A TLD is known as the domain suffix 26 Top Level Domain Names 27

10 Host Files Text file that associates TCP/IP host names with IP addresses Alias Nickname for a node s host name 28 Host Files On a UNIX-based computer a host file is: Called hosts Located in the /etc/hosts On a Windows computer, a host file: Is also called hosts What is the file lmhosts? Must be located in the c:\windows directory in order to be recognized by the operating system c:\windows\system32\drivers\etc\hosts 29 Domain Name System (DNS) Hierarchical way of tracking domain names and their addresses, devised in the mid-1980s 30

11 Configuring DNS 31 DDNS (Dynamic DNS) RFC 2136 DNS is reliable as long as host s address is static Many Internet users subscribe to the type of Internet service in which IP address changes periodically In DDNS, service provider runs program on user s computer that notifies service provider when IP address changes DNS record update effective throughout Internet in minutes 32 Zeroconf (Zero Configuration) Collection of protocols designed by IETF to simplify setup of nodes on TCP/IP networks Assigns IP address (local address) Resolves node s host name and IP address without requiring DNS server r Discovers available services Enables directly connected workstations to communicate without relying on static IP addressing IP addresses are assigned through IPv4LL (RFC 3927) 33

12 NetBIOS and NetBEUI NetBIOS originally designed to provide Transport and Session layer services for applications running on small, homogenous networks Microsoft added standard L2/L3 layer component called NetBEUI Efficient on small networks Consumes few network resources Provides excellent error correction Does not allow for good security Few possible connections Cannot be routed 34 Discussions What is the protocol that supports file sharing and printer sharing on Windows? Answer: NetBIOS NetBIOS is a transport and session layer protocol. What is the L2/L3 protocol for NetBIOS. Answer: NetBUEI originally Is NetBUEI on most Windows today? Answer: NO What is the L2/L3 protocol for NetBIOS? TCP/IP 35 How to Transfer Files NetBIOS NetBUEI Ethernet File Transfer NetBIOS FTP HTTP TFTP TCP UDP IP Ethernet Q: which one is the best? 36

13 Windows Internet Naming Service (WINS) Provides a means of resolving NetBIOS names with IP addresses WINS offers several advantages Guarantees a unique NetBIOS name is used for each computer on a network Support for DHCP Better network performance Supported but not needed in Windows 2000 (or later) Where is the setting for WINS in Windows 2000? 37 ICMP Internet Control Message Protocol Packet Internet Groper (PING): utility that can verify that TCP/IP is installed, bound to the NIC, configured correctly, and communicating Pinging: i Echo request and echo reply Can ping either an IP address or a host name Pinging loopback address, , to determine whether workstation s TCP/IP services are running 38 Transmission Control Protocol (TCP) TCP Provides reliable data delivery services Connection-orientedoriented subprotocol Requires establishment of connection n between communicating nodes before protocol will transmit data TCP segment Holds TCP data fields Becomes encapsulated by IP datagram 39

14 Transmission Control Protocol (TCP) Port: Address on host where application makes itself available to incoming data 40 TCP: 3-way hand-shaking process 41 UDP 42

15 TCP/UDP Sockets and Ports Socket Defined in TCP and UDP Logical address assigned to a specific process running on a host computer The socket s s address combines the host computer s IP address with the port number associated with a process Socket ::= IP address + Port Number Port numbers in the range of 0 to 1023 are called well-known ports 43 TCP/UDP Sockets and Ports 44 TCP/UDP Sockets and Ports 45

16 Review: IP Address Shortage Short term solution: CIDR i.e., IP Subnetting Network Address Translation (NAT) Long term solution: IPv6 46 NAT for Home and SOHO Networks ISP DSL/Cable modem Internet NAT Router Question: How can one use a private IP address to surf the public Internet? Answer: Network Address Translation (NAT) 47 How does NAT work? Internet D-port =21 NAT Router D-port =21 FTP S-port =2001 S-port =1234 Server D-IP = D-IP = S-IP = S-IP = D-port =2001 S-port =21 D-IP = S-IP = D-port =1234 S-port =21 D-IP = S-IP = Note: the sender and receiver do not know anything about NAT. 48

17 If my web server is behind the NAT router, can I make it available to the public? ISP DSL/Cable modem (web server) (ftp server) Internet NAT Router port Virtual Address Virtual Port , 8000, , 8000, IP Address Assignment Static IP address IP address manually assigned to a device Servers usually have static IP addresses. Network device (switches, routers, etc.) also uses static IP address. Dynamic IP address DHCP and BOOTP Manages dynamic distribution of IP addresses on a network Workstation usually use DHCP. 50 Dynamic Host Configuration Protocol (DHCP) Automated means of assigning a unique IP address to every device on a network Reasons for implementing DHCP Reduce the time and planning spent on IP address management Reduce the potential for errors in assigning IP addresses Enable users to move their workstations and printers without having to change their TCP/IP configuration Make IP addressing transparent for mobile users 51

18 DHCP Leasing Process Lease Agreement between DHCP server and client on how long the client will borrow a DHCP-assigned IP address 52 Terminating a DHCP Lease A DHCP lease may expire based on the period established for it in the server configuration A DHCP lease may be manually terminated at any time from either the client s TCP/IP configuration or the server s DHCP configuration Release The act of terminating a DHCP lease 53 Can you do DHCP across LAN Segment? Answer: Yes, BOOTP Relay. 3. BOOTP Relay 2. BOOTP Relay BOOTP Relay 6. BOOTP Relay DHCP Server 4. Assign DHCP supports BOOTP relay. Client 1. What is my IP address? 7. My IP address is

19 Addressing in IPv6 Also known as IP next generation or IPng Slated to replace the current IP protocol, IPv4 Perhaps the most valuable advantage IPv6 offers over IPv4 is its promise of billions and billions of additional IP addresses through its new addressing scheme (128 bits) Address format: F:F:0:0:0:0:3012:0CE3 000F:000F:0000:0000:0000:0000:3012:0CE3 8 (4 4))=1284))=128 bits F:F::3012:0CE3 Representing IPv4 in IPv6: :: Addressing in IPv6 Unicast address Type of IPv6 address that represents a single interface on a device Multicast address Type of address in IPv6 that represents multiple interfaces, often on multiple nodes No Broadcast address Anycast address Type of address specified in IPv6 that represents a group of interfaces, any of which can accept a transmission 56 TCP/IP Application Layer Protocols Hypertext Transport Protocol (HTTP) Telnet Used to log on to remote hosts using TCP/IP protocol suite File Transfer Protocol (FTP) Used to send and receive files via TCP/IP Simple Mail Transfer Protocol (SMTP) Responsible for moving messages from one server to another, using the Internet and other TCP/IP-based networks Simple Network Management Protocol (SNMP) Manages devices on a TCP/IP network 57

20 SMTP (Simple Mail Transfer Protocol) Protocol responsible for moving messages between mail servers over TCP/IP-based networks Belongs to Application layer of TCP/IP Model Relies on TCP at Transport layer Operates from port 25 Relies on higher-level programs for instructions Can only transport or hold mail When configuring clients to use Internet , must identify user s SMTP server 58 MIME (Multipurpose Internet Mail Extensions) Standard SMTP message format allows for lines that contain 1000 ASCII characters max Cannot handle pictures or formatted text MIME: standard d for encoding and interpreting ti binary files, images, video, and non-ascii character sets within messages Identifies each element of a message according to content type Works in conjunction with SMTP 59 POP (Post Office Protocol) Application layer protocol used to retrieve messages from mail servers POP3 is most current and commonly used version Mail delivered and stored on mail server until user connects (via client) to retrieve messages Mail deleted from server after retrieval Minimizes use of server resources Best suited to users who retrieve mail from same workstation all the time 60

21 IMAP (Internet Message Access Protocol) Developed as sophisticated alternative to POP3 IMAP4 is most current version Users can store messages on mail server IMAP4 provides the following features: Retrieve all or only a portion of any mail message Review messages and delete them while the messages remain on the server Create sophisticated methods of organizing messages on the server Share mailboxes in a central location 61 Hypertext Transport Protocol (HTTP) Protocol that Web clients and servers use to communicate Forms the backbone of the Web On TCP Hypertext Markup Language (HTML) Language that defines formatting standards for Web documents 62 Hypertext Transport Protocol (HTTP) Figure 11-18: Web client/server transmission using HTTP 63

22 FTP and TFTP FTP: File transfer over TCP TFTP File transfers over UDP No login Simple acknowledgement and sequence control 64 NTP Network Time Protocol (NTP): Application layer protocol used to synchronize clocks of computers 65 Windows/Linux Utilities Commands on Windows to help you configure and trouble shooting network problems ping check connectivity netstat/route see routing table and TCP sessions nbtstat (windows only) NetBIOS info ipconfig/ifconfig IP address and interface info tracert/traceroute find all routers between src and dst Nslookup/dig DNS (IP address and hostname mapping) arp mapping of IP and MAC addresses 66

23 Review Questions Compare TCP/IP to the OSI Model If I give you the IP datagram and leave out 4-5 data fields, can you fill in those blank fields in the datagram? Given an IP address, can you tell its IP address class? Class A, B, or C. Describe the problem of IPv4 address shortage. What are the two short term solutions and one long term solution to address this problem? Give a network with multiple IP subnets, can you populate the routing table on the router? What are the long term and short term solutions to the problem of IP address shortage? 67 Review Questions (cont.) ARP: What is it? How does it work? Is it a protocol on IP? Is it a protocol on Ethernet? Populate the ARP table for a network. Trace IP packets and Ethernet frames on a network. Show three different protocol stacks that support file transfers 68 Review Questions (cont.) UDP uses only four data fields in TCP. What are these four fields? What is DNS? Why do we need it? If your DNS server is down, can you surf the Internet? If data in the /etc/hosts file is hacked,, how does it affect the upper layer services? What are the port numbers for the FTP, telnet, DNS, SNMP, HTTP, TFTP, and finger? Given an IPv4 address, can you change it to the IPv6 format? 69

24 Review Questions (cont.) What is NAT and how is it used? What are the datagram fields changed by NAT? Trace IP packets before and after the NAT router. What are the differences between BOOTP and DHCP? Which one is better and used today? Can DHCP work across multiple LAN segments? How? WINS: What is it? What is it for? Is it needed on today s network? Windows vs. Linux utilities. 70 Review Questions (cont.) How do you find the IP address of How do you find the internet name of ? How do you find the number of hops (number of routers) from DePaul University to Purdue University? What are the differences between FTP and TFTP? Give three examples of protocols on TCP. Give two examples of protocols on UDP. Give a protocol to send and a protocol to receive . 71