Address Resolution. Address Resolution. Address Resolution

9/30/2014 Name and Address Resolution Overview Name and address resolution  Naming with the DNS  Domain Name System (DNS) BSAD 141 Dave Novak Sou...
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9/30/2014

Name and Address Resolution

Overview Name and address resolution  Naming with the DNS 

Domain Name System (DNS) BSAD 141 Dave Novak Sources: Network+ Guide to Networks, Dean 2013

Name / Address Resolution 

Name 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

The process of mapping a fully qualified domain name (FQDN) to an IP address • dnovak.bsad.uvm.edu = 132.198.50.156



Name / Address Resolution

Address Resolution 

The process of mapping an IP address to a MAC address • 137.99.106.156 = 00-D0-09-A7-B5-0C

Address Resolution 

Why is address resolution necessary?



IP address = 132.198.50.156



Domain name = dnovak.bsad.uvm.edu

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….

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Name Resolution 

Why is name resolution necessary?

TCP/IP to NetBIOS 

Network Basic Input/Output System 

Layer of software or application programming interface (some consider it a protocol)

TCP/IP Name Resolution 

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



IP address to fully qualified domain name

In general, independent of protocol stack used



Non-hierarchical



Uses its own naming system

Purpose: Isolate the application from the actual hardware used in the LAN



IP address to NetBIOS name



• Allows applications to communicate with networking hardware, and the LAN itself

TCP/IP to NetBIOS



TCP/IP to NetBIOS

• Interface for PCs to access LAN resources



Historically, two general types of mapping



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 

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 

• Name resolution occurs using broadcast

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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

HOSTS files 

Static system that does not scale to meet the needs of the internet 

TCP/IP to FQDN 



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

Directory services 

Directory service

C:\Windows\system32\drivers\etc • HOSTS – ASCII text file used by TCP/IP computers to resolve FQDN to IP addresses

Directory services 

Two basic versions of FQDN resolution

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



What does it mean to be Authenticated?

Domains 

What is a domain?



Why are domains used?

• Complex hierarchical databases that store information about network resources

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Directory services

Domain controller 

Computer designated for storing and processing directory service information 

Database of user accounts and what privileges each user has



Authentication information

Active directory 

Hierarchical tree



Works with domains

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 structure

Container objects – hold other containers or leaves Leaf objects – represent network resources such as users, groups, computers, etc

• Multiple domains can be grouped together into a tree • Multiple trees can be grouped together into a forest

Domain Name System (DNS)

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



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

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DNS 

Internet uses Domain Naming System (DNS) for name resolution



DNS 

Active Directory uses hierarchical structure similar to DNS for name resolution on the LAN

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

Structure of computer names com



Top-level DNS (centrally managed) 

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

http://www.iana.org/domains/root/db

org edu vt

www.uvm.edu

ncsu 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

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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:

Name resolution 

NetBIOS and FQDN mapping to IP address serve same purpose – name resolution 

• Finds a mapping in its local data base • Forwards the request to a remote DNS root server which resolves the request

• NetBIOS names are non-hierarchical • FQDNs are hierarchical

• Returns an error because the request cannot be resolved (no name exists)

Address resolution 

ARP and RARP

Make it easier for people to remember computer names by mapping between the IP address and a name that can be understood by people



In either case, name must be mapped to IP

Summary Concepts 

MAC / hardware / physcial address in hexidecimal form (layer 2)



MAC address to IP





IP to MAC





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

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Summary Concepts 

FQDN



NetBIOS name





dnovak.bsad.uvm.edu dnovaktab

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