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Name resolution

Unit objectives Discuss the role of the HOSTS file and

DNS Discuss the role of NETBIOS,

LMHOSTS file and WINS

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Topic A

Topic A: The HOSTS file and Domain Name System

Topic B: NetBIOS Name Resolution

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Name Resolution The process of converting the “friendly”

(i.e., domain) name to its IP address Is handled through four different methods

– HOSTS files – LMHOSTS files – WINS servers – DNS servers

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Name Resolution

The following example illustrates the difference between a URL (Uniform Resource Locator) and a domain name:– URL: http://www.example.net/index.htm– Domain name: www.example.net – Registered domain name: example.net

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Host name resolution

Name resolution using a HOSTS file uses a locally stored ASCII text file

This ASCII text file can be edited by using any ASCII text editor

Each HOSTS file entry will contain– An IP address – A TAB or SPACE – One or more symbolic names

Each IP address should appear only once in the HOSTS file

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Sample HOSTS file # Copyright (c) 1998 Microsoft Corp. # This is a sample HOSTS file used by Microsoft TCP/IP stack for

Windows98 # This file contains the mappings of IP addresses to host names.

Each # entry should be kept on an individual line. The IP address should # be placed in the first column followed by the corresponding host

name. # The IP address and the host name should be separated by at least

one # space. # Additionally, comments (such as these) may be inserted on

individual # lines or following the machine name denoted by a '#' symbol. # For example: # 102.54.94.97 rhino.acme.com # source server # 38.25.63.10 x.acme.com # x client host 127.0.0.1 localhost

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Host name resolution Host names are case-sensitive

– They use ASCII (American Standard Code for Information Interchange)

– As opposed to EBSIDIC – (Extended Binary Coded Decimal Interchange Code)

W hen using HOSTS name resolution– Edit the sample HOSTS file– Include the IP addresses and host names

with which you need to communicate

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Host name resolution You can use a FQDN in the HOSTS file

– A FQDN is an unambiguous domain name that specifies the exact location in the Domain Name System's tree hierarchy through to a top-level domain and finally to the root domain.

– For example, given a device with a local hostname of myhost and a default parent domain name of example.com:

– the fully qualified domain name is myhost.example.com. It therefore uniquely defines the device — there may be many hosts in the world called myhost,

there can only be one myhost.example.com.

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Activity A-1 page 11-4

Discussing HOSTS files

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Domain Name System DNS is a hierarchical naming system

for identifying hosts on a private network or on the Internet

The hierarchical structure identifying domain names is called the domain name space

Each domain can be divided into sub-domains,

and these into host names, Each with a period acting as a delimiter

between each portion of the name.

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The Domain Name System

subdomains

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The DNS domains

DNS domains you might encounter:– Organizational domains

com edu gov mil net org

– Country domains us - United States au - Australia ca - Canada

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The DNS name resolution

DNS names are maintained and managed through DNS servers – DNS servers contain information about

all the domains they support

DNS servers are also supported at the sub-domain level, which will contain the host name information – Subdomains can be further divided into

logical zones, with a server managing all of the hosts for that zone

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Domain Name Resolution

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Domain Name Resolution

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The DNS client configuration You can use the DNS tab in the Advanced

TCP/IP Settings of Local Area Connection’s TCP/IP Properties to configure a Windows 2000/Server 2003/XP computer– Right click My Network Places/Properties/Local

Connection/Properties/TCP-IP/Properties

The specifications in the DNS tab are– Specify the DNS Server addresses in the

order you want to use them– Primary & connection-specific DNS suffixes– DNS suffixes– E.g., see next 2 slides:

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Specifies that resolution for unqualified names that are used on this computer are limited to the domain suffixes of the primary suffix and all connection-specific suffixes.

Connection-specific suffixes are configured in DNS suffix for this connection.

The primary DNS suffix is configured by clicking Properties on the Computer Name tab (System/Control Panel).

Local setting is used only if the associated Group Policy is disabled or unspecified.

The DNS client configuration

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For example, if your primary DNS suffix is “dev.wcoast.microsoft.com” and you type “ping xyz” at a command prompt, the computer queries for “xyz.dev.wcoast. microsoft.com.”

If you also configure a connection-specific domain name on one of your connections for “bldg23.dev.wcoast. microsoft.com”, the computer queries for “xyz.dev.wcoast.microsoft.com” and “xyz.bldg23.dev.wcoast.microsoft.com.”

The DNS client configuration

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Advanced TCP/IP Settings, DNS tab

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Activity A-2 page 11-10

Discussing Domain Name System

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Topic B

Topic A: The HOSTS file and Domain Name System

Topic B: NetBIOS Name Resolution

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NetBIOS

An OSI Model Session layer (TCP/IP model Application layer) interface between the network operating system and lower-level functions

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NetBIOS Image #1

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NetBIOS Image #2

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Image #3

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NetBIOS The NetBIOS API allows applications on

separate computers to communicate over a local area network.

In modern networks, it normally runs over TCP/IP (NetBIOS over TCP/IP, or NBT), giving each computer in the network both a NetBIOS name and an IP address corresponding to a (possibly different) host name.

Older operating systems ran NetBIOS over IPX/SPX or IEEE 802.2 (NBF).

NetBIOS provides services related to the session layer of the OSI model.

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NetBIOS In order to connect to a computer running TCP/IP

via its NetBIOS name, the name must be resolved to a network address, usually an IP address.

The NetBIOS name-IP address resolution is done either by broadcasts or a WINS Server - NetBIOS Name Server).– The NetBIOS name is 16 characters, however Microsoft

limits the host name to 15 characters and reserves the 16th character as a NetBIOS Suffix.

– This suffix describes the service or name record type such as host record, master browser record or domain controller record.

– The shortened host name is specified when Windows networking is installed/configured.

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Activity B-1 Page 11-12

Discussing NETBIOS

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The LMHOSTS keywords Some entries in the LMHOSTS file are

. preceded by a pound sign (#)– In most cases, this indicates a comment line

This is like the HOSTS file, except that not all of the entries preceded by “#” are comments!

Some of them are used to identify special keywords “#PRE” - will cause the entry to be preloaded into the

name cache. “#DOM:domain” - will associate the entry with the domain

specified by <domain>. This affects how the browser and logon services behave in

TCP/IP environments. To preload the host name associated with #DOM entry, it is

necessary to also add a #PRE to the line. The <domain> is always preloaded although it will not be

shown when the name cache is viewed.

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The LMHOSTS keywords “#INCLUDE:filename” - will force the RFC NetBIOS

(NBT) # software to seek the specified <filename> and parse it as if it were # local.

is generally a UNC-based name, allowing a centralized lmhosts file to be maintained on a server.

It is ALWAYS necessary to provide a mapping for the IP address of the server prior to the #INCLUDE.

This mapping must use the #PRE directive.

– “#BEGIN_ALTERNATE” / “#END_ALTERNATE” The #BEGIN_ and #END_ALTERNATE keywords allow

multiple #INCLUDE statements to be grouped together.

Any single successful include will cause the group to succeed.

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Introducing WINS

“Windows Internet Name Service”, or WINS, is an automated way of supporting NetBIOS address resolution– It does away with the necessity of

maintaining static LMHOSTS files on each Windows-based machine on the network

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The WINS client configuration You can configure

Windows 2000/XP /Server 2003 WINS clients by accessing the “Advanced TCP/IP Settings” of a LAN connection

Then activate the WINS tab - see figure to left:

With >1 WINS server, put them in order, using “Add”

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Activity B-2 Page 11-16

Discussing the LMHOSTS file and WINS

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Unit summary

Discussed the role of the HOSTS file and DNS

Discussed the role of NETBIOS, LMHOSTS file, and WINS