networking chapter 10

Network NamingNetwork Naming

Chapter 10

ObjectivesObjectives• Describe the function and capabilities of DNS • Configure and troubleshoot WINS• Use common TCP/IP utilities to diagnose

problems with and WINS

OverviewOverview

Introduction to NamingIntroduction 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)

• 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)

Figure 10.1 Turning names into numbers

Three Parts to Chapter 10Three Parts to Chapter 10

• DNS• WINS• Diagnosing TCP/IP Networks

DNSDNS

• 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

DNSDNS

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• Name Spaces– Home-brewed DNS

• Must not connect to the Internet• Set up a DNS server to be the root server

Figure 10.2 Our People name space

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

• 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

Figure 10.4 Private DNS network

Figure 10.5 Two DNS domains

Figure 10.6 Subdomains added

• 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

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

Figure 10.7 A single SOA can support one or more domains

Figure 10.8 DNS flexibility

Figure 10.9 New information passed out

Figure 10.10 Root server in action

Figure 10.11 DNS domain

• 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

• 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

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

Figure 10.13 Routers don’t forward broadcasts!

Figure 10.14 A host contacts its local DNS server

Figure 10.15 DNS information in Windows

Figure 10.16 Entering DNS information in Ubuntu

Figure 10.17 IPCONFIG /ALL showing DNS information in Windows

Figure 10.18 Checking the DNS cache

Figure 10.19 Talking to a root server

Figure 10.20 Talking to a root server

Figure 10.21 Talking to microsoft.com DNS server

• 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

• DNS Servers (in action)– Three special storage areas

• Cached Lookups• Forward Lookup Zones• Reverse Lookup Zones

Figure 10.22 DNS server main screen

Figure 10.23 Inspecting the DNS cache

• DNS Servers (in action)– Cache-only DNS servers

• Do not store lookup zones• Talk to other DNS servers to resolve for clients

Figure 10.24 Authoritative vs. cache-only DNS server

• 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

• 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

Figure 10.25 Forward lookup zone totalhome

Figure 10.26 Less common DNS record types

• Forward lookup zones– Two types of forward lookup zones: Primary

zone and Secondary zone– Resolve FQDN to IP address with Reverse

lookup zone

Figure 10.27 Two DNS servers with updating taking place

Figure 10.28 Reverse lookup zone

• 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

• 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)

Figure 10.29 NetBIOS broadcast

• 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

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

• 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

• 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

Figure 10.31 Joining a workgroup

Figure 10.32 Two workgroups in Network folder

• 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

Figure 10.33 Logging into the domain

• 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

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

• 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)

Figure 10.35 Updating DNS information in Windows

• 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

Figure 10.36 DNS error

• 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

Figure 10.37 Using PING to check DNS

• 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

• 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

• Troubleshooting DNS– UNIX/Linux tool: domain information

grouper (DIG)• Similar to NSLOOKUP• Non-interactive• Ask it a question; it answers

DNSDNS

• Legacy NetBIOS– Current versions of Windows use DNS

and/or CIFS– NetBIOS names supported for downward

compatibility– NetBIOS system broadcasts its name

WINSWINS

• Prior to CIFS– LMHOSTS file

• Works for NetBIOS like HOSTS does for DNS• Microsoft OSs still support• Every Windows systems has an LMHOSTS file

• 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

Figure 10.38 WINS server

Figure 10.39 WINS server

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

WINS server

• 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

Diagnosing TCP/IP Diagnosing TCP/IP NetworksNetworks

• 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

• 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

• 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

Figure 10.40 NET VIEW in action

Figure 10.41 NETSTAT in action

Figure 10.42 Using TRACERT