System and Network Administration Chapter 2

System and Network
Administration
Chapter Four
Bule Hora University
1

Host Names vs. IP addresses
 Host names
◦ Mnemonic name appreciated by humans
◦ Variable length, full alphabet of characters
◦ Provide little (if any) information about location
◦ Examples: www.google.com and www.bhu.edu.et
 IP addresses
◦ Numerical address appreciated by routers
◦ Fixed length, binary number
◦ Hierarchical, related to host location
◦ Examples: 64.236.16.20 and 212.58.224.131
3

Human Involvement
4
 If you want to…
◦ Call someone, you need to ask for their phone
number
 You can’t just dial “X”
◦ Mail someone, you need to get their address first
 What about the Internet?
◦ If you need to reach Google, you need their IP
◦ Does anyone know Google’s IP?
 Problem:
◦ People can’t remember IP addresses
◦ Need human readable names that map to IPs

Internet Names and Addresses
5
 Addresses, e.g. 129.10.117.100
◦ Computer usable labels for machines
◦ Conform to structure of the network
 Names, e.g. www.bhu.edu.et
◦ Human usable labels for machines
◦ Conform to organizational structure
 How do you map from one to the other?
◦ Domain Name System (DNS)

NEED FOR DNS
To identify an entity, TCP/IP protocols use the IP
address, which uniquely identifies the connection of
a host to the Internet.
However, people prefer to use names instead of
numeric addresses. Therefore, we need a system that
can map a name to an address or an address to a
name.

7
 Eventually, the hosts.txt system fell apart
◦ Not scalable, couldn’t handle the load
◦ Hard to enforce uniqueness of names
 e.g ASTU
 Adama Science and Technology University?
 Addis Ababa Science andTechnology University?
◦ Many machines had inaccurate copies of
hosts.txt
 Thus, DNS was born

Towards DNS
Host Names vs. IP addresses
 Names are easier to remember
www.cnn.com vs. 64.236.16.20 (but not tiny urls)
8

9
What is DNS?
 DNS is a host name to IP address
translation service
 DNS is
◦ a distributed database implemented in a
hierarchy of name servers
◦ an application level protocol for message
exchange between clients and servers

10
Why DNS?
 It is easier to remember a host name than it is
to remember an IP address.
 An name has more meaning to a user than a 4
byte number.
 Applications such as FTP, HTTP, email, etc., all
require the user to input a destination.
 The user generally enters a host name.
 The application takes the host name supplied by
the user and forwards it to DNS for translation
to an IP address.

11
How does it work?
 DNS works by exchanging messages
between client and server machines.
 A client application will pass the
destination host name to the DNS
process (in Unix referred to as the
gethostbyname() routine) to get the IP
address.
 The application then sits and waits for the
response to return.

Lecture 13: 02-22-2005 12
Domain Name System
 A lookup mechanism for translating objects into
other objects
 Users generally prefer names to numbers
 Computers prefer numbers to names
 DNS provides the mapping between the two
◦ I have “x”, give me “y”
 DNS is NOT a directory service
◦ No way to search the database
 No easy way to add this functionality
 A globally distributed, loosely coherent, scalable,
reliable, dynamic database

Lecture 13: 02-22-2005 13
Domain Name System Goals
 Basically a wide-area distributed database
 Scalability
 Decentralized maintenance
 Robustness
 Global scope
◦ Names mean the same thing everywhere

DNS at a High-Level
14
 Domain Name System
 Distributed database
◦ No centralization
 Simple client/server architecture
◦ UDP port 53, some implementations also use
TCP
 Hierarchical namespace
◦ As opposed to original, flat namespace
◦ e.g. .com  google.com  mail.google.com

Naming Hierarchy
15
 Top Level Domains (TLDs) are at
the top
 Maximum tree depth: 128
 Each Domain Name is a subtree
◦ .edu  neu.edu  ccs.neu.edu 
www.ccs.neu.edu
 Name collisions are avoided
◦ neu.com vs. neu.edu
Root
edu com gov mil org
net uk fr etc.
neu bhu
ccs ece husky
www login mail

16
Root DNS Servers
com DNS servers org DNS servers edu DNS servers
poly.edu
DNS servers
umass.edu
DNS servers
yahoo.com
DNS servers
amazon.com
DNS servers
pbs.org
DNS servers
Distributed, Hierarchical Database
Client wants IP for www.amazon.com; 1st approx:
 client queries a root server to find com DNS server
 client queries com DNS server to get amazon.com DNS
server
 client queries amazon.com DNS server to get IP address for
www.amazon.com

17
TLD and Authoritative Servers
 Top-level domain (TLD) servers:
◦ responsible for com, org, net, edu, etc, and all top-level
country domains uk, fr, ca, jp.
◦ Network Solutions maintains servers for com TLD
◦ Educause for eduTLD
 Authoritative DNS servers:
◦ organization’s DNS servers, providing authoritative
hostname to IP mappings for organization’s servers (e.g.,
Web, mail).
◦ can be maintained by organization or service provider

25.18
Mapping a name to an address or an address to a
name is called name-address resolution.
Basic Domain Name Resolution

Recursive DNS Query
19
 Puts the burden of resolution
on the contacted name server
 How does know who to
forward responses too?
◦ Random IDs embedded in DNS
queries
 What have we said about
keeping state in the network?
Root
com
ns1.google.com
www.google.com
asgard.ccs.neu.edu
Where is www.google.com?

20
Recursive vs. Iterative Queries
 Recursive query
◦ Ask server to get
answer for you
◦ E.g., request 1
and response 8
 Iterative query
◦ Ask server who
to ask next
◦ E.g., all other
request-response
pairs requesting host
cis.poly.edu
root DNS server
local DNS server
dns.poly.edu
1
2
3
4
5
6
authoritative DNS server
dns.cs.umass.edu
7
8
TLD DNS server

21
DNS Caching
 Performing all these queries takes time
◦ And all this before actual communication takes place
◦ E.g., 1-second latency before startingWeb download
 Caching can greatly reduce overhead
◦ The top-level servers very rarely change
◦ Popular sites (e.g., www.cnn.com) visited often
◦ Local DNS server often has the information cached
 How DNS caching works
◦ DNS servers cache responses to queries
◦ Responses include a “time to live” (TTL) field
◦ Server deletes cached entry afterTTL expires

DNS components
There are 3 components:
 Name Space:
Specifications for a structured name space
and data associated with the names
 Resolvers:
Client programs that extract information
from Name Servers.
 Name Servers:
Server programs which hold information
about the structure and the names.
22

DNS Name Space
 The name space is the structure of the DNS database
◦ An inverted tree with the root node at the top
 Each node has a label
◦ The root node has a null label, written as “”
23
third-level node
second-level node second-level node
top-level node
third-level node third-level node
second-level node
top-level node
second-level node second-level node
top-level node
The root node
""

25.24
Domain name space
To have a hierarchical name space, a domain name
space was designed. In this design the names are
defined in an inverted-tree structure with the root at the
top. The tree can have only 128 levels: level 0 (root) to
level 127.

DNS Name Space
 Domain Names
 A domain name is the sequence of labels from a node to the root,
separated by dots (“.”s), read left to right
◦ The name space has a maximum depth of 127 levels
◦ Domain names are limited to 255 characters in length
 A node’s domain name identifies its position in the name space
25
dakota
west
tornado
east www
nominum metainfo
com
berkeley nwu
edu gov
nato
int
army
mil
uu
net org
""

DNS Name Space
 SubDomain Names
 One domain is a subdomain of another if its
apex node is a descendant of the other’s apex
node
 More simply, one domain is a subdomain of
another if its domain name ends in the other’s
domain name
◦ So sales.nominum.com is a subdomain of
 nominum.com
 com
◦ nominum.com is a subdomain of com
26

DNS Name Space
 Delegation
 Administrators can create subdomains to group hosts
◦ According to geography, organizational affiliation or any other
criterion
 An administrator of a domain can delegate
responsibility for managing a subdomain to someone
else
◦ But this isn’t required
 The parent domain retains links to the delegated
subdomain
◦ The parent domain “remembers” who it delegated the
subdomain to
27

DNS Name Space
 Delegation Creates Zones
 Each time an administrator delegates a
subdomain, a new unit of administration is
created
◦ The subdomain and its parent domain can now be
administered independently
◦ These units are called zones
◦ The boundary between zones is a point of delegation
in the name space
 Delegation is good: it is the key to scalability
28

Dividing a Domain into Zones
nominum.com
domain
nominum.com
zone
ams.nominum.com
zone
rwc.nominum.com
zone
.arpa
acmebw
molokai skye
rwc www ftp
gouda cheddar
ams
nominum netsol
.com .edu
""
Tree is divided into zones
Each zone has an
administrator
Responsible for the
part of the heirarchy

DNS Name Servers
 Name servers store information about the
name space in units called “zones”
◦ The name servers that load a complete zone are said
to “have authority for” or “be authoritative for” the
zone
 Usually, more than one name server are
authoritative for the same zone
◦ This ensures redundancy and spreads the load
 Also, a single name server may be authoritative
for many zones
30

Types of Name Servers
 Two main types of servers
◦ Authoritative – maintains the data
 Master – where the data is edited
 Slave – where data is replicated to
◦ Caching – stores data obtained from an authoritative
server
◦ The most common name server implementation
(BIND) combines these two into a single process
 Other types exist…
 No special hardware necessary

Name Server Architecture
 You can think of a name server as part:
◦ database server, answering queries about the
parts of the name space it knows about (i.e., is
authoritative for),
◦ cache, temporarily storing data it learns from
other name servers, and
◦ agent, helping resolvers and other name
servers find data that other name servers
know about

Copyright © 2001, Nominum,
Inc.
DNS Name Resolution
 Name resolution is the process by which
resolvers and name servers cooperate to find
data in the name space
 To find information anywhere in the name
space, a name server only needs the names and
IP addresses of the name servers for the root
zone (the “root name servers”)
◦ The root name servers know about the top-level
zones and can tell name servers whom to contact for
allTLDs

Inc.
Name Resolution
 A DNS query has three parameters:
◦ A domain name (e.g., www.google.com),
 Remember, every node has a domain name!
◦ A class (e.g., IN), and
◦ A type (e.g., A)
 A name server receiving a query from a
resolver looks for the answer in its
authoritative data and its cache
◦ If the answer isn’t in the cache and the server isn’t
authoritative for the answer, the answer must be
looked up

Inc.
ping www.google.com.
The Resolution Process
 Let’s look at the resolution process step-
by-step:
annie.west.sprockets.com

Inc.
What’s the IP address
of
www.nominum.com?
 The workstation annie asks its configured name
server, dakota, for www.nominum.com’s address
dakota.west.sprockets.com

Inc.
 The name server dakota asks a root name server, m, for
www.nominum.com’s address
m.root-servers.net
of
www.nominum.com?

Inc.
 The root server m refers dakota to the .com name servers
 This type of response is called a “referral”
m.root-servers.net
dakota.west.sprockets.com Here’s a list of the
com name servers.
Ask one of them.

Inc.
 The name server dakota asks a com name server, f,
for www.nominum.com’s address
m.root-servers.net
of
www.nominum.com?
f.gtld-servers.net

Inc.
 The com name server f refers dakota to the
nominum.com name servers
f.gtld-servers.net
m.root-servers.net
Here’s a list of the
nominum.com
name servers.
Ask one of them.

Inc.
 The name server dakota asks an nominum.com name
server, ns1.sanjose, for www.nominum.com’s address
f.gtld-servers.net
m.root-servers.net
ns1.sanjose.nominum.net
of
www.nominum.com?

Inc.
 The nominum.com name server ns1.sanjose
responds with www.nominum.com’s address
f.gtld-servers.net
m.root-servers.net
Here’s the IP
address for
www.nominum.com

Inc.
Here’s the IP
address for
www.nominum.com
 The name server dakota responds to annie with
www.nominum.com’s address
f.gtld-servers.net
m.root-servers.net

DNS MESSAGES
DNS has two types of messages:
query message and
Response message .
Both types have the same format. The query
message consists of a header and question records;
the response message consists of a header, question
records, answer records, authoritative records, and
additional records.

Window Deployment Service
 Windows Deployment Services role in
Windows Server 2012 is the updated and
redesigned version of Remote
Installation Services (RIS).
 Windows Deployment Services enables
you to deploy Windows operating
systems. You can use it to set up new
computers by using a network-based
installation
48

 Windows Deployment Services enables you
to manage images and un attend
installation scripts, and provide attended
and unattended installation options.
 Windows Deployment Services facilitates
basic configuration of installations, including:
Partitioning and formatting physical media
Installing the operating system and post-
configuration tasks
Simplifying installation
Providing consistency across your computer
environment
49

 Windows Deployment Services is
intended for administrators who are
responsible for deployment of new
computers in medium and large
organizations.
50

 In order forWDS to work,
You must have a network card and an active
network connection.
Your computer must be connected to and
registered with the campus network and
using the campus DHCP servers.
AD DS (Active Directory Domain Services) A
Windows Deployment Services server must be
either a member of an AD DS (Active
Directory Domain Services) domain or a
domain controller for an AD DS domain.
51

 DHCP You must have a working DHCP
Server with an active scope on the
network because Windows Deployment
Services uses PXE, which relies on DHCP
for IP addressing .
 PXE (Windows Pre-Boot Execution
Environment ):-all allows you to use other
PXE servers on campus
52

 DNS You must have a working DNS
Server on the network before you can
runWindows Deployment Services.
 NTFS volume the server running
Windows Deployment Services requires
an NTFS File system volume for the
image store.
 Credentials to install the role, you must
be a member of the Local
Administrators group on the server.
53

ISCSI
 ISCSI is Internet SCSI (Small Computer
System Interface), an Internet Protocol
(IP)-based storage networking standard
for linking data storage facilities.
 ISCSI is used to facilitate data transfers
over intranets and to manage storage
over long distances.
54

ISCSI
 The iSCSI protocol is among the key technologies
expected to help bring about rapid development
of the storage area network (SAN) market, by
increasing the capabilities and performance of
storage data transmission.
 Because of the ubiquity of IP networks, iSCSI
can be used to transmit data over local area
networks (LANs), wide area networks (WANs),
or the Internet and can enable location-
independent data storage and retrieval.
55

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