Lecture 9 Unix Networking (see chapter 7)

1. Lecture 9 Unix Networking(see chapter 7) Unix Networking & Internetworking History Overview DNS Typical Communication Utilities

2. Network History • Internet research started in the 1960’s • ARPA – Advanced Research Planning Agency • Began work on packet switching. • ARPANET – late 1970’s

3. TCP/IP • Prototype Internet was developed. • Transmission Control Protocol/ Internet Protocol • 1st used by academic institutions, research organizations, & the U.S. military.

4. Internet Growth • 1983 – Internet sites = 562 • 1986 – Internet sites = 2,308 • Doubled every year for the next 10 years. • 1996 – 9.5 million

5. Web Browser • Key to easy network utilization. • 1st browser – Mosaic – Developed by NCSA • National Center for Supercomputer Applications. • Launched in 1991 • Web browsing surpassed FTP • File Transfer Protocol

6. Size Now • Between 50 – 100 million computers • 1 million computer networks • Unix has a special role in that most of the network protocols were initially implemented on Unix platforms. • Most servers run on Unix based machines.

7. Networks & Internetworks • Two or > hardware resources connected. • Can be computers, printers, plotters, scanners, etc. • A hardware resource is a host.

8. A typical network configuration

9. Network Types • LAN – Local Area Network • MAN – Metropolitan Area Network • WAN – Wide Area Network • These distinctions are based on the maximum distance between hosts.

10. LAN • Local Area Network • Hosts are in a room, building, or close buildings • Distance from a few meters to about 1km

11. MAN • Metropolitan Area Networks • Hosts between a city or between small cities • Distance between hosts is about 1 to 20 km

12. WAN • Wide Area Network • Hosts distance range from tens of kilometers to a few thousand kilometers.

13. Internetwork • Internetwork is a network of networks. • Can connect networks within a campus or networks thousands of kilometers apart. • Connected with routers or gateways. • Internet is an internetwork of tens of thousands of networks

14. Routers & Gateways • Routers – Connect similar networks • Gateways – Connect dissimilar networts. Convert messages to suitable form for each network.

15. Reasons for Networks • Sharing resources – Printers, plotters, scanners, software, etc. • Communication between people • Costs savings • Reliability > 1 computer

16. TCP/IP • Kernel handles the communications. • The communications hardware (NIC) • Network Interface Card • The Unix kernel handles the details.

17. DNS Name Server • Domain name service (DNS) is central to the Internet • When URLs are entered in a Web browser, a DNS server converts the name to an IP address, allowing the client to send a packet to the Web server as requested • The information in DNS can be thought of as an inverted hierarchical tree, where the top of the tree is called root and is represented by a period • Users typically don’t refer to roots, but to the last part of domain names called top-level domains

18. DNS Name Server

19. DNS Name Server

20. Setting Up a DNS Name Server • Resolving a domain to an IP address using DNS, also called querying the DNS server, stores, or caches, the conversion information resulting in speedier DNS queries • Each domain has a master DNS server which contains database files that provide IP addresses to every host in that domain • Each domain should have a slave DNS server which acts as a backup to the master

21. Setting Up a Basic Name Server • The program that implements a DNS server is called named, the name daemon, which is controlled by a system script in /etc/rc.d/init.d • named is found in the BIND package on most Linux systems; selecting the Red Hat Linux name server component provides bind-conf, bind-utils, and caching-nameserver • Caching name servers have no preconfigured domain information, but simply query other DNS servers and cache the results

22. Name Server • Resolver functions like: • gethostbyname • To invoke DNS service • Maps a host name to its IP address • gethostbyaddr • Maps an IP address to its hostname

23. View Information • ifconfig command • View the IP address & other info about your hosts interface to the network. • Usually in the /sbin directory • (Type /sbin/ifconfig)

24. View Information • nslookup • Display the IP address of a host • nslookup ibm.com • Returns the address. • Modern forms: host or dig

25. Popular Internet Services • Electronic Mail – SMTP (Simple Mail Transfer Protocol) • File Transfer – FTP (File Transfer Protocol) • Remote Login – Telnet (and ssh) • Time – Time • Web Browsing – HTTP (Hyper Text Transfer Protocol)

26. Client-Server Model • Internet services are implemented by service partitioned in two parts. • Part on the computer (host) where the user is logged onto is the client software. • The part that starts running when a server boots is the server software.

27. Client-Server • The server runs forever – • Waiting for a client request • A request is handled & then waits for another request. • Client starts running when a user runs the program for a service the client offers.

28. Web Site • URL – Universal Resource Locator • URL is given to the client process to view a page. • http://machine • Displays the home page of machine

29. List of users • List of users using hosts on a network. • rwho – Remote who • Displays users using machines on your network. • rwho –a Users currently idle

30. Testing a network Connection • ping – If host is alive it echoes a datagram. • whereis – Finds the location • finger – Display information about a user

31. Problem Areas • Size of networks continues to grow. • Big problem – Too many servers. • Usually one server per application – 1 for data base, 1 for accounting, etc.

32. Virtualization • Virtualize the many servers employed. • One server with the capability of replacing many specialized servers. • Goldman Sachs (brokerage firm) – Had 250 network people & 30 million lines of specialized code. • Large number of servers, regional, intl., etc.

33. Virtualization • The number of specialist can be greatly reduced. • The network complexity can also be reduced. • The one major problem is having one machine for critical functions.

34. Typical Communication Utilities in UNIX

35. The talk Command

36. A Complete talk Session

37. A Complete talk Session

38. A Complete talk Session

39. The write Command

40. E-Mail Programs • Some Programs available in Unix/Linux • Mail – most basic, low level mail command • ELM • PINE (PINE Is Not Elm), more user friendly text mail • Outlook, GUI driven • Eudora • Netscape Mailer

41. Email Address

42. The mail command

43. The mail command • You can use the mail command in several ways: • mail -- by itself, it opens your messages and lets you read them • mail person@address -- lets you compose a message to someone at a certain address. • mail -s (subject) person@address -- lets you send a message to someone at an address, with a certain subject. • mail -s (subject) person@address < text_file -- lets you send a message to someone with text_file as the body of the email.

44. Using mail • When you are writing the mail message body, use ^D or <enter> . <enter> to end editing and send the message. • If cc: shows up, this is a list of other addresses you can enter if you wish to send a message to other people. • ^C will kill a mail message you are typing.

45. The mail Command (Sending Mail)

46. Header Editing • While editing a message you may use… • ~h -- lets you edit the header (to, subject, cc, bcc) • These may also work: • ~s -- edit the subject. • ~t -- edit the to list. • ~c -- edit the cc (carbon copy) list. • ~b -- edit the bcc (blind carbon copy) list.

47. Message Editing Commands • Use these while writing the actual message • ~r <file> -- Add a file into the message. • ~f <num> -- add another email into the message (forwarding). • ~w <file> -- write the message to a file. • ~q -- quit without saving • ~p -- print the contents of the message.

48. Mail Command Example

49. The mail Command (Read Mail)

50. Mail reading commands • These commands are used in mail at the & prompt • q -- quit and save • x -- quit without making any changes. • R or r -- reply to a message (r = senders and recipients, R = senders only.) • f <numbers> -- view the message headers. • p or t <numbers> -- show those messages