1. Network Naming
Chapter 10

2. Objectives
• Describe the function and capabilities of DNS
• Configure and troubleshoot WINS
• Use common TCP/IP utilities to diagnose
problems with and WINS

3. Overview

4. Introduction to Naming
• Computers use IP addresses to communicate
• People remember names better than
numbers
• Name resolution created to convert names to
IP addresses (and vice versa)

5. • Name resolution has evolved over the years
• Main protocol is Domain Name System (DNS)
• Operating systems support old and new
• Windows, Linux, and Macintosh OS X still
support Windows Internet Name Server
(WINS)

6. Figure 10.1 Turning names into numbers

7. Three Parts to Chapter 10
• DNS
• WINS
• Diagnosing TCP/IP Networks

8. DNS

9. DNS
• Early Internet use of HOSTS file
– One file copied to all hosts on the Internet
– Contained a list of IP addresses for every
computer, matched to system names
– Preceded rules for composing Internet
names

10. • HOSTS file
– Preceded DNS
– Anyone could name computer anything
– Duplicate names not allowed
– Sample old HOSTS file:
• 192.168.2.1 fred
• 201.32.16.4 SCHOOL2
• 123.21.44.16 SERVER

11. • HOSTS file
– Hosts file updated on every system every
morning at 2 a.m.
– Impractical after Internet grew to 5000
– New name system, but HOSTS file still
exists
– # symbol indicates a line is a comment

12. • HOSTS file
– Every OS first looks in HOSTS file
– Follow-up to Try This!
• Every TCP/IP app looks at HOSTS file
• If you altered the HOSTS file per the Try This!
enter this command:
ping timmy

13. • HOSTS file
– Some place shortcut names in a HOSTS file
to avoid typing a long name into browser
– DNS is more powerful and used much
more

14. • How DNS works
– No single computer can handle all Internet
name resolution
– Delegation used
• Top-dog DNS system delegates parts of the job
• Subsidiary DNS systems delegate parts of their
work
• All DNS servers run a special DNS server program

15. • How DNS works
– Naming system facilitates delegation
– Top-dog DNS a bunch of powerful systems
• Dispersed around the world
• Known collectively as the DNS root servers (or
DNS root)
– The Internet name for DNS root is “.”
– Below root are the top-level domain servers

16. • Name Spaces
– Hosts file uses a flat name space
– DNS uses a hierarchical name space
• A hierarchy of DNS domains and computer names
• Hierarchical DNS names space is the DNS Tree
• Root is the holding area to which all domains
connect
• Individual computers have host names

17. • Name Spaces
– Home-brewed DNS
• Must not connect to the Internet
• Set up a DNS server to be the root server

18. Figure 10.2 Our People name space

19. Figure 10.3 Two DATA.TXT files in different
directories on the same system

20. • Name Spaces
– DNS naming syntax
• Opposite of disk folder/directory syntax
• A complete DNS name is a fully qualified domain
name (FQDN)
• Host and all domains in order
• Root is far right

21. Figure 10.4 Private DNS network

22. Figure 10.5 Two DNS domains

23. Figure 10.6 Subdomains added

24. • Name Servers
– One server is authoritative DNS server for a
domain
• a.k.a. Start of Authority (SOA)
• Other name servers (NS) are subordinate
• All DNS servers know the address of SOA and all
NS servers in the domain
• SOA keeps others updated

25. • Name Servers
– Other systems send queries to DNS servers
– Request resolution of FQDNs to IP addresses

26. Figure 10.7 A single SOA can support one or
more domains

27. Figure 10.8 DNS flexibility

28. Figure 10.9 New information passed out

29. Figure 10.10 Root server in action

30. Figure 10.11 DNS domain

31. • Name Resolution
– DNS not required to access Internet
– DNS just makes is much easier
– IP addresses required for connections
– Most people would not use Internet without
DNS name resolution

32. • Name Resolution
– Type Web address into a browser
– It must resolve the name to IP address
– Three ways to resolve a name
• Broadcasting
• HOSTS file
• Querying a DNS server

33. Figure 10.12 Any TCP/IP-savvy program accepts
either an IP address or an FQDN

34. Figure 10.13 Routers don’t forward broadcasts!

35. Figure 10.14 A host contacts its local DNS server

36. Figure 10.15 DNS information in Windows

37. Figure 10.16 Entering DNS information in Ubuntu

38. Figure 10.17 IPCONFIG /ALL showing DNS information
in Windows

39. Figure 10.18 Checking the DNS cache

40. Figure 10.19 Talking to a root server

41. Figure 10.20 Talking to a root server

42. Figure 10.21 Talking to microsoft.com DNS server

43. • DNS Servers (in action)
– Most OSs have built-in DNS server software
• Server versions of Windows
• Most versions of UNIX/Linux
– Third-party DNS servers

44. • DNS Servers (in action)
– Three special storage areas
• Cached Lookups
• Forward Lookup Zones
• Reverse Lookup Zones

45. Figure 10.22 DNS server main screen

46. Figure 10.23 Inspecting the DNS cache

47. • DNS Servers (in action)
– Cache-only DNS servers
• Do not store lookup zones
• Talk to other DNS servers to resolve for clients

48. Figure 10.24 Authoritative vs. cache-only DNS server

49. • Totalhome domain example
– Does not comply with Internet rules
– None of the computers is visible on Internet
– Only usable on private network
– Forward lookup is named totalhome
– All the DNS servers listed under NS records

50. • Totalhome forward lookup zone
– Each system in the domain has an A record
– An alias for a system is a canonical name
(CNAME)
– SMTP servers use MX records (Mail eXchanger)
– AAAA records are for IPv6 addresses

51. Figure 10.25 Forward lookup zone totalhome

52. Figure 10.26 Less common DNS record types

53. • Forward lookup zones
– Two types of forward lookup zones: Primary
zone and Secondary zone
– Resolve FQDN to IP address with Reverse
lookup zone

54. Figure 10.27 Two DNS servers with updating
taking place

55. Figure 10.28 Reverse lookup zone

56. • Windows DNS server
– Performs most functions exactly like
UNIX/Linux DNS servers
– Adds a Windows-only Active Directory-
integrated zone
– Avoids problems of standard DNS servers
– All domain controllers are DNS servers
– All DNS servers are equal

57. • Enter Windows
– 1980s Microsoft NetBIOS/NetBEUI
– 1990s Microsoft created NetBIOS over
TCP/IP – added NetBIOS naming to DNS
– Old sharing protocol Server Message Block
(SMB)

58. Figure 10.29 NetBIOS broadcast

59. • Enter Windows—NetBIOS over TCP/IP
– New sharing protocol Common Internet File
System (CIFS)
– SMB/CIFS adopted by UNIX/Linux and Mac
OS X
– CIFS and DNS work together

60. Figure 10.30 Samba on Ubuntu (it’s so common that the OS
doesn’t even use the term in the dialog box)

61. • Living with the Legacy of CIFS
– Networks using CIFS use two name systems
– CIFS broadcast to find local server
– DNS query to find TCP/IP host
– CIFS and DNS work together

62. • Living with the Legacy of CIFS
– CIFS organizes computers into workgroups
– Computer joins a workgroup
– Flat name space
– See workgroups in Network/My Network
Places

63. Figure 10.31 Joining a workgroup

64. Figure 10.32 Two workgroups in Network
folder

65. • Living with the Legacy of CIFS
– Computers controlled by Windows domain
controller server are grouped in a Windows
domain
– Windows Computers join a domain
– Computers (and users) authenticate to the
domain
– Windows domains now use DNS naming

66. Figure 10.33 Logging into the domain

67. • Living with the Legacy of CIFS
– An Active Directory domain is an
organization of computers that shares one
or more Windows domains
– All Active Directory Windows domain
controllers are DNS servers
– All domain controllers are equal partners

68. Figure 10.34 If one domain controller goes down,
another automatically takes over

69. • Active Directory-Integrated Zones
– DNS system not reliant on a single server
– Windows DHCP servers automatically
update all client information in the Active
Directory-integrated zone
– In some cases the client updates DNS
– Non-Windows systems can only update
Activity Directory-Integrated Zones using a
Windows client (like Samba)

70. Figure 10.35 Updating DNS information in Windows

71. • Troubleshooting DNS
– Client is source of most DNS problems
– DNS servers rarely go down
– If a DNS server is down, clients use
secondary DNS server
– Symptom: “server not found” error

72. Figure 10.36 DNS error

73. • Troubleshooting DNS
– Eliminate any local DNS caches
• Do not use Web browser for troubleshooting
• Run ipconfig /flushdns
• PING the name of a well-known Web site
– Does it return IP address?
– If not, PING an IP address

74. Figure 10.37 Using PING to check DNS

75. • Troubleshooting DNS
– If the previous steps indicate a problem with
the DNS server, run NSLOOKUP run
• Queries functions of DNS servers
• Depends on proper permission level
• Use to change how your system uses DNS

76. • Troubleshooting DNS
– Run NSLOOKUP without parameters to get
• IP address and name of default DNS server
• Error indicates primary DNS server is down or
client has wrong IP for DNS server
• NSLOOKUP has own prompt

77. • Troubleshooting DNS
– UNIX/Linux tool: domain information
grouper (DIG)
• Similar to NSLOOKUP
• Non-interactive
• Ask it a question; it answers

78. DNS

79. WINS
• Legacy NetBIOS
– Current versions of Windows use DNS
and/or CIFS
– NetBIOS names supported for downward
compatibility
– NetBIOS system broadcasts its name

80. • Prior to CIFS
– LMHOSTS file
• Works for NetBIOS like HOSTS does for DNS
• Microsoft OSs still support
• Every Windows systems has an LMHOSTS file

81. • Windows Internet Naming Service (WINS)
– WINS server for legacy Windows
– No broadcasting: NetBIOS hosts register
with WINS
– Allows NetBIOS to function in a routed
network
– WINS proxy agent for legacy Windows

82. Figure 10.38 WINS server

83. Figure 10.39 WINS server

84. • Configuring WINS clients
– Enter IP address of WINS server
– WINS information can be added to DHCP
– WINS clients register NetBIOS names with
WINS server

85. • Troubleshooting WINS
– Most “WINS” problems are NetBIOS
problems
• Two systems sharing same name
• Change name of one system
– NBTSTAT
• Check name cache with nbtstat –c
• Determine if WINS server has given inaccurate info

86. Diagnosing TCP/IP
Networks

87. • Improper configuration causes most
problems
• PING anyone you want to connect to
• Regardless of what the user cannot
connect to, you perform the same steps

88. • Use common sense
– If one system behaves differently than others,
the problem is with the client
– Before starting steps (below) check the network
connections and protocols

89. • Steps for troubleshooting TCP/IP
– Diagnose the NIC
– Diagnose locally
– Check IP address and subnet mask
– Run NETSTAT with no options
– Run netstat –s
– Diagnose to the gateway
– Diagnose to the Internet

90. Figure 10.40 NET VIEW in action

91. Figure 10.41 NETSTAT in action

92. Figure 10.42 Using TRACERT