CIT 500: IT Fundamentals

1. CIT 500: IT Fundamentals Networking

2. Topics • LANs and WANs • TCP/IP Layers • IP Addressing and Routing • SSH remote logins • Web access • Network commands

3. Networks Networks are groups of connected computers. • Wired: ethernet, frame relay. • Wireless: 802.11, bluetooth. Scales • LAN • WAN • Internetwork Hardware • Network Interface Cards (NICs) • Hubs and switches • Routers

4. Circuit vs Packet Switching Circuit-switched: A connection called a circuit is set up between two devices and used for the whole communication. Packet-switched: Data is chopped up into small pieces called packets and sent over the network. Each packet may follow a different path between the communicating parties.

5. Circuit vs Packet Switching

6. Logical and Physical Network Paths Logical network path Send me the web page at http://nku.edu/. Here’s the HTML data for that page. PC Server Physical network path Router Switch Server Switch PC Router

7. Local Area Networks • Network covering a small physical area, i.e. an office up to a campus. • LAN Hardware • Network Interface Card (NIC) • Twisted pair cabling. • RJ45 connectors.

8. Broadcast Local Delivery • Send message to every PC on network. • Each PC checks address that message was sent to. • If address matches address of PC, PC accepts message. Hub

9. Switched Local Delivery Initial Switch Table Switch learns location of PCs. Ex: A sends message to C. • Switch receives traffic on port 1. • Adds A to table for port 1. • Switch sends message to all ports but 1. C A B D Final Switch Table 2 3 1 4 Switch

10. Ethernet MAC Addresses • OUI assigned by IEEE. • Burned in address (BIA) stored in ROM. • Can be replaced with a local address.

11. Switch Hardware Switch ports can plug into • Other switches. • Hubs. • PCs or other end devices. Rack-mounted Switch Small Home/Office Switch

12. Building larger LANs What if you run out of ports? • Plug a switch into one of the ports. What if you run out of port/MAC table space? • Build larger tables—for every host in world? • Use routing. How is routing different from switching? • Structured addresses allow grouping of hosts.

13. Routing Logic PC1: If host on same Ethernet, send; otherwise, send to gateway router. R1, R2: Lookup destination in route table and forward packet to specified router. R3: Lookup destination in route table and send to local Ethernet.

14. 172 . 16 . 254 . 1 10101100 00010000 11111110 00000001 1 byte 32 bits = 4 bytes IP Addresses 32-bit integers One for each network interface. Dotted decimal notation: ii.jj.kk.ll

15. Grouping IP Addresses Groups of consecutive IP addrs are called networks. Routing table would only need 3 entries below.

16. Network and Host Parts IP addresses are divided into two parts • Network ID (like zip code) • Host ID (like street address) • Two special IP addresses • Network address (e.g. 130.4.0.0) • Broadcast address (e.g. 130.4.255.255)

17. CIT 384: Network Administration

18. Assigning Addresses ICANN assigns network numbers. • Internet Corporation for Assigned Network Numbers. • ICANN gives authority to regional orgs, e.g. ARIN (American Registry for Internet Numbers) • Typically to ISPs, universities, corporations. ISP assigns IP addresses within network

19. Why WANs? The obvious answer: distance • Ethernet can’t travel over many miles. • You don’t have the rights-of-way to run a cable over many miles between sites. Solution: point-to-point leased line.

20. What is the Internet? • The Internet isn't complicated • The Internet isn't a thing. It's an agreement. • The Internet is stupid. • Adding value to the Internet lowers its value. • All the Internet's value grows on its edges. • The Internet's three virtues:a. No one owns itb. Everyone can use itc. Anyone can improve it From http://www.worldofends.com/

21. Internet Standards IETF (Internet Engineering Task Force) • Open group responsible for Internet standards. RFC (Request for Comments) • Internet standard documents. • IETF archives RFCs at www.ietf.org. IANA (Internet Assigned Numbers Authority) • Coordinates unique network numbers. • IP addresses, protocol numbers, etc. ICANN (Inet. Corp. for Assigned Names & Numbers) • Manages DNS top level domains (TLDs) like .com, .gov • Gives domain registrars responsibilities over domains.

22. History of Internet 1969 ARPAnet created (4 hosts) 1984 DNS deployed 1986 Cleveland Freenet offers free Internet access 1987 Number of hosts reaches 10,000 1988 Morris Worm 1989 Number of hosts reaches 100,000 1990 First commercial dialup ISP 1991 WWW released at CERN 1992 Number of hosts reaches 1,000,000 1993 Mosaic, graphical web browser, released 1994 First banner ads appear on the web 1995 AOL offers Internet access 1996 Telcos try to ban Internet telephones 1996 Number of hosts reaches 10,000,000 2000 Number of hosts reaches 100,000,000

23. The Domain Name System CIT 140: Introduction to IT

24. Dig: DNS Lookup dig [options] Purpose Interact with name servers specified in /etc/resolv.conf and display their responses Output Responses of name servers for queries sent to them Commonly used option/features: -f file For batch operation , take domain names (or IP addresses) from ‘file -p port Interact with a name server at ‘port’ instead of the default port53 CIT 140: Introduction to IT

25. Dig Example > dig www.google.com ; <<>> DiG 8.3 <<>> www.google.com ;; res options: init recurs defnam dnsrch ;; got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 2 ;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 5, ADDITIONAL: 0 ;; QUERY SECTION: ;; www.google.com, type = A, class = IN ;; ANSWER SECTION: www.google.com. 14m40s IN CNAME www.l.google.com. www.l.google.com. 4m40s IN A 72.14.203.104 www.l.google.com. 4m40s IN A 72.14.203.99 CIT 140: Introduction to IT

26. SSH Remote Login

27. SSH Features Secure login ssh –l user host Secure remote command execution ssh –l user host command Secure file transfer sftp –l user host scp file user@host:/tmp/myfile

28. The Problem of Passwords • Good passwords are hard to remember. • Password transferred to remote system. • Automating remote access with passwords is difficult.

29. Key-based Authentication SSH has a public-key authentication feature. Private key stored in your machine. Public key stored on remote machines. Public-key login protocol • Client sends server a login request. • Server issues a challenge. • Client responds with computation based on challenge and private key. • Server checks response with public key.

30. Using key-based authentication • Generate a public/private key pair. ssh-keygen Encrypted key files: id_dsa, id_dsa.pub • Copy public key to remote host Copy to ~/.ssh/authorized_keys. • Login to remote host ssh –l user remote

31. Keys are more secure than Passwords • Need to have two items to login: key file and passphrase. • Neither key nor passphrase is sent to remote host. • Machine-generated cryptographic keys are infeasible to guess, unlike passwords.

32. SSH Agent Problem: you have to enter passphrase to decrypt the key each time you use ssh. Solution: SSH Agent > ssh-agent $SHELL > ssh-add Enter passphrase for /home/jw/.ssh/id_dsa: ******** Identity added: /home/you/.ssh/id_dsa (/home/jw/.ssh/id_dsa) > ssh –l jw host

33. SSH Agent Features Agent support for entire session. Start ssh-agent on initial shell. X: ~/.xsession (Often enabled by default.) Multiple keys ssh-add keyfile ssh-add –l Remove keys ssh-add –d keyfile ssh-add –D

34. Text-based web browsers Widely used text-based browsers • Lynx • Links Advantages • Support for blind users. • Privacy: no image-based web bugs. • Performance. • Use –dump option for non-interactive use.

35. wget wget URL – non-interactive network download -o file Save URL to specified file. -c Continue getting partially downloaded file. -p Download all support files (images, css, js.) -k Change links to point to local files (-k –p) -r Recursively download links in target. -t # Retry specified number of times (default 20)

36. Ping • Test to see if remote host is available. • If connection fails, test link by link • Ping system on your LAN. • Ping closest router. • Ping next router. • … • Ping target system. • One link will fail if cannot reach remote host. • Use –c option to specify number of packets.

37. Traceroute Tracks path through each router to destination • Reports which routers the packets passed through • Reports how much time it took for each hop Useful for identifying network problems • Identify which links are down • Identify which links are slow Remote traceroutes via www.traceroute.org.

38. ifconfig ifconfig [-a] int – configure a network interface Only root can modify settings. [-a] list settings for all interfaces int list settings for the specified interface int Linux typically uses eth0, eth1 for Ethernet

39. hostname hostname – show or set system’s host name; may or may not include DNS domain. dnsdomainname – show or set system’s DNS domain name.

40. References • Daniel J. Barrett, Robert G. Byrnes, Richard E. Silverman, SSH, The Secure Shell, 2nd edition, O’Reilly, 2005. • Wendell Odom, CCNA Official Exam Certification Library, 3rd edition, Cisco Press, 2007. • Bill Parkhurst, Routing First-Step, Cisco Press, 2005. • Doc Searls and David Weinberger, World of Ends, http://www.worldofends.com/, 2003. • W. Richard Stevens, TCP/IP Illustrated, Addison-Wesley, 1994 • Nicholas Wells, The Complete Guide to Linux System Administration, Thomson Course Technology, 2005.