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

2. Overview
Name and address resolution
Naming with the DNS

3. Name / Address Resolution
Name Resolution
The process of mapping a fully qualified domain name (FQDN) to an IP address
dnovak.bsad.uvm.edu =
Address Resolution
The process of mapping an IP address to a MAC address
= 00-D0-09-A7-B5-0C

4. 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 =
Domain name = dnovak.bsad.uvm.edu

5. Address Resolution
Why is address resolution necessary?

6. Address Resolution
TCP/IP suite Address Resolution Protocol (ARP) / RARP
The protocol responsible for mapping IP –to- MAC and vice versa
Reverse ARP (RARP) MAC to IP
Ensures devices agree on how to resolve addresses
More on ARP/RARP next class….

7. Name Resolution
Why is name resolution necessary?

8. TCP/IP Name Resolution
Historically, two general types of mapping
IP address to NetBIOS name
IP address to fully qualified domain name

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. Directory services Directory service
What does it mean to be Authenticated?

17. 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

18. Domains
What is a domain?
Why are domains used?

19. Domain controller
Computer designated for storing and processing directory service information
Database of user accounts and what privileges each user has
Authentication information

20. Directory services
In a P2P architecture, why wouldn’t a centralized directory service work?
What are some benefits of a centralized directory service?

21. 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

22. Active directory Hierarchical structure Container objects – hold other
containers or leaves
Leaf objects – represent network
resources such as users, groups,
computers, etc
Hierarchical structure

23. 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

24. 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

25. DNS Internet uses Domain Naming System (DNS) for name resolution
Active Directory uses hierarchical structure similar to DNS for name resolution on the LAN

26. 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

27. DNS Top-level DNS (centrally managed)

28. Structure of computer names
gov
org
edu
com vt
ncsu
uvm
www
ftp
gopher
Each discrete zone or level is separated
By a period. The rightmost entry is the
Most generic and the leftmost, the most
specific

29. Structure of computer names
Once domain name is registered domain owner manages internal structure of domain and can create subdomains

30. 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

31. 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

32. How it works Video we watch in class:
Video that you should watch outside of class:

33. 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)

34. 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

35. Address resolution
ARP and RARP
MAC address to IP
IP to MAC

36. Summary Concepts
MAC / hardware / physcial address in hexi- decimal form (layer 2)
00-C4-J BE
Cannot be resolved off LAN/subnet
IP / software / network address in binary form (layer 3)
Devices on the internet communicate using network addresses
Routers maintain tables that allow them to recognize MAC addresses of devices on their LAN

37. Summary Concepts
FQDN
dnovak.bsad.uvm.edu
NetBIOS name
dnovaktab