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
