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 –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….

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 Hierarchical structure

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 gov org edu com vt ncsu uvm www ftp gopher 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 www.uvm.edu

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.com/watch?v=72snZctFFtA

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 hexi- decimal 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