2. Objectives
• Describe the function and capabilities of DNS
• Configure and troubleshoot WINS
• Use common TCP/IP utilities to diagnose
problems with and WINS
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)
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
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
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
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
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
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
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)
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
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
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)
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
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
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
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
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
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
Teaching Tip If the students have access to computers with an Internet connection, have them take time to do the Try This on page 246. If their computers are running Windows, they will find the HOSTS file in the locations provided in the paragraph immediately above the exercise. However, they will only be successful if they have full access to the HOSTS file, including the ability to save it back to the same location. You may have to tinker with the permissions on the computers in order to allow the students to do this. If these are lab computers, and you are not permitted or inclined to change the security, then consider giving a demonstration. If you have full control of a computer with a projector connected, be prepared to simply demonstrate this on your computer. That will mean checking out the exercise before class. Now, the point of the exercise is that the HOSTS file may be archaic, but it is powerful in the right or wrong hands. There are good reasons why the recent versions of Windows protect this file so fiercely. A HOSTS file can be used to lock down a network, and it can also be used maliciously. I experienced both situations in computer training labs.
Teaching Tip If you have not done so, introduce the concept of name space here, but do not go into detail (it is a topic head later in the chapter). Point out that the HOSTS file came into being when the Internet had a flat name space, whereas DNS is a hierarchical name space. This is true, even though HOSTS files still work today.
Teaching Tip The Test-specific information begins here.
Teaching Tip The Tip on the bottom of Page 247 points out that DNS servers use TCP and UDP port 53. Teaching Tip Per Note on Page 247: “The DNS root for the entire Internet consists of 13 powerful DNS server clusters scattered all over the world.” Make sure the students understand that a cluster consists of many servers. Also, have them go to www.root-servers.org , or do so for them, and share the information you find there.
Teaching Tip The TRACERT command does a reverse lookup when you use an IP address rather than an FQDN. If you need to find the FQDN associated with an IP address, do a TRACERT on the address.
