Transcript Name Resolution

Name and Address
Resolution
Domain Name System
(DNS)
BSAD 141
Dave Novak
Sources: Network+ Guide to Networks,
Dean 2013
Overview
Name and address resolution
 Naming with the DNS

Name / Address Resolution

Name Resolution

The process of mapping a fully qualified
domain name (FQDN) to an IP address
• dnovak.bsad.uvm.edu = 132.198.50.156

Address Resolution

The process of mapping an IP address to a
MAC address
• 137.99.106.156 = 00-D0-09-A7-B5-0C
Name / Address Resolution

Computers use binary network level
addressing and hexi-decimal hardware
addressing

Humans use base 10 numbering and
alphabet

Protocols hide these differences from users

IP address = 132.198.50.156

Domain name = dnovak.bsad.uvm.edu
Address Resolution

Why is address resolution necessary?
Address Resolution


TCP/IP suite Address Resolution Protocol
(ARP) / RARP

The protocol responsible for mapping IP –toMAC and vice versa

Reverse ARP (RARP) MAC to IP

Ensures devices agree on how to resolve
addresses
More on ARP/RARP next class….
Name Resolution

Why is name resolution necessary?
TCP/IP Name Resolution

Historically, two general types of mapping

IP address to NetBIOS name

IP address to fully qualified domain name
TCP/IP to NetBIOS

Network Basic Input/Output System

Layer of software or application
programming interface (some consider it a
protocol)
• Interface for PCs to access LAN resources
• Allows applications to communicate with
networking hardware, and the LAN itself

Purpose: Isolate the application from the
actual hardware used in the LAN
TCP/IP to NetBIOS

In general, independent of protocol stack used

Non-hierarchical

Uses its own naming system

Win OS prior to Win 2000 used NetBIOS names

Win XP stores its name using hierarchical naming
(similar to DNS) instead of NetBIOS

NetBIOS names are installed in a flat-file database

NetBIOS names contain NO network identifier
TCP/IP to NetBIOS

Historically, two basic versions of NetBIOS
name resolution in Windows

1) NetBEUI

The default networking protocol stack on
early versions of Windows OS

No longer installed by default on Windows
systems
• Non-routable
• Name resolution occurs using broadcast
TCP/IP to NetBIOS

2) Windows Internet Naming Service
(WINS)

Service provided in NT and 2000 that
registers NetBIOS names and IP addresses
of LAN devices and than resolves NetBIOS
 IP as needed

Allows users to access resources that have
NetBIOS names

If not using WINS, then LMHOST is needed
TCP/IP to FQDN

To make address scalability and ambiguity
issues, fully qualified domain names
(FQDN) / absolute domain name were
developed

Hierarchical

URLs rely on this naming scheme

Specifies all domain levels – uniquely
identifying the device
TCP/IP to FQDN

Two basic versions of FQDN resolution

1) DNS (more on this in a bit)

2) HOSTS file
• Every computer must have a HOSTS file to
resolve the IP / FQDN for any computer it
wishes to communicate with
• Names stored in a flat-file system on local PC
called HOSTS file
HOSTS files

Static system that does not scale to meet
the needs of the internet

C:\Windows\system32\drivers\etc
• HOSTS – ASCII text file used by TCP/IP
computers to resolve FQDN to IP addresses
Directory services

Directory service

What does it mean to be Authenticated?
Directory services

Form of the directory service is determined
by the logical architecture

P2P: Each computer maintains its own
information on user accounts and security
settings

C/S: Centralized security / user account
database or directory service
• Complex hierarchical databases that store
information about network resources
Domains

What is a domain?

Why are domains used?
Domain controller

Computer designated for storing and
processing directory service information

Database of user accounts and what
privileges each user has

Authentication information
Directory services

In a P2P architecture, why wouldn’t a
centralized directory service work?

What are some benefits of a centralized
directory service?
Active directory

Microsoft’s enterprise directory service for
Win 2000 server and beyond

Hierarchical tree

Works with domains
• Multiple domains can be grouped together into a
tree
• Multiple trees can be grouped together into a
forest
Active directory

Hierarchical structure
Container objects – hold other
containers or leaves
Leaf objects – represent network
resources such as users, groups,
computers, etc
Active directory
Transitive TRUST relationships
A trusts B, B trusts C, so A trusts C
Different from Win NT Server TRUST
Structure where relationships were
not transitive
Domain Name System
(DNS)

Technique for mapping FQDN to IP
address

NetBIOS naming is rarely used today

TCP/IP has replaced NetBEUI as the
default protocol on MS Windows OS

DNS has largely replaced NetBIOS as the
default method of name resolution
• Internet outgrew flat file naming systems
• Provides hierarchical naming
DNS

Internet uses Domain Naming System
(DNS) for name resolution

Active Directory uses hierarchical structure
similar to DNS for name resolution on the
LAN
DNS

DNS hierarchy

Domain name

Host name

Read from right to left
• Name on far right represents top of domain
hierarchy
• Name to far left is host
DNS

Top-level DNS (centrally managed)

http://www.iana.org/domains/root/db
Structure of computer
names
com
www.uvm.edu
Each discrete zone or level is separated
By a period. The rightmost entry is the
Most generic and the leftmost, the most
specific
gov
org
edu
vt
ncsu
www.uvm.edu
uvm
www
ftp
gopher
Structure of computer
names

Once domain name is registered domain
owner manages internal structure of domain
and can create subdomains
DNS

Split administrative responsibility between
central body and individual domain owners

Thousands of domains

Millions of hosts

Impossible for one central sources to keep all
information current

No single DNS server contains complete
listing of all names
DNS

DNS servers contain IP addresses of
several root name servers

Root name servers maintain list of top-level
domains and IP addresses of those domain
servers

Authoritative server
How it works
Video we watch
in class:
http://www.youtube.com/
watch?v=eX7Yt_fxAfU
Video that you
should watch
outside of class:
http://www.youtube.co
m/watch?v=72snZctFF
tA
DNS

Clients/host are configured to request name
resolution from a specific DNS server

Check ipconfig /all to see the address of the DNS
server you use

The DNS server accepts the request and either:
• Finds a mapping in its local data base
• Forwards the request to a remote DNS root server which
resolves the request
• Returns an error because the request cannot be resolved
(no name exists)
Name resolution

NetBIOS and FQDN mapping to IP address
serve same purpose – name resolution

Make it easier for people to remember
computer names by mapping between the IP
address and a name that can be understood
by people
• NetBIOS names are non-hierarchical
• FQDNs are hierarchical

In either case, name must be mapped to IP
Address resolution

ARP and RARP

MAC address to IP

IP to MAC
Summary Concepts

MAC / hardware / physcial address in hexidecimal form (layer 2)



00-C4-J0-00-65-BE
Cannot be resolved off LAN/subnet
IP / software / network address in binary form
(layer 3)



137.99.116.1
Devices on the internet communicate using network
addresses
Routers maintain tables that allow them to recognize
MAC addresses of devices on their LAN
Summary Concepts

FQDN


dnovak.bsad.uvm.edu
NetBIOS name

dnovaktab