DHCP and network configuration. cisco networks

1. Computer Networks
Hamayun Khan
Lecturer CS & IT
Superior University, Lahore
hamayun.khan@superior.edu.pk

2. From previous lecture

3. DNS &
DHCP

4.  Explain the concept of DNS.
 Explain the principle of DHCP.

6.  DNS is an acronym of Domain Name System. As the name
suggests, DNS is a naming system that gives a name to
any computer or service connected to a network. DNS is
utterly important and everyone should use it. Without it,
we’d have to visit websites through their IP addresses,
rather than their domain. So, for example, if you wanted
to visit our website through it’s IP address, you’d have to
go to 209.135.140.30. But with DNS, you can go to
rosehosting.com . It’s easier to remember and it’s more
user-friendly. That’s why people consider DNS “the phone
book of the Internet”. Nobody wants to remember an IP,
but everyone can and does remember a domain name.

9.  There’s lots of stuff going on “behind the scenes”
when you visit a website. There’s a communicating
relationship between a few servers and your
computer.These are the usual steps they take:
1. The user enters the website’s domain in the address
bar
2. The browser and OS check their local cache
3. The Resolver checks the local cache
4. The root server checks the local cache
5. The root server forwards the resolver to the TLD
server
6. Receiving the answer

11.  Forward Lookup Zone
 Reverse Lookup Zone

12. Dynamic Host Configuration Protocol

13.  In IP environment, before a computer can
communicate to another one, they need to
have their own IP addresses.
 There are two ways of configuring an IP
address on a device:
 Static: Statically assign an IP address. This
means we manually type an IP address for this
computer
 Dynamic Use a protocol so that the computer
can obtain its IP address automatically.

15.  Lease Generation Process
 DORA Process
 Discover
 Offer
 Request
 Acknowledgement
 Four step Process

16. Range of IP
Addresses
Different Scopes
for different
subnets

17.  DHCPDISCOVER
message
 Destination IP address
255.255.255.255
(broadcast)
 Destination MAC address
FF-FF-FF-FF-FF-FF
(broadcast)
 Source IP address 0.0.0.0
 Source MAC Address
 Try to find out a DHCP
Server

18.  DHCPOFFER message
 IP Address
 Subnet Mask
 Default Gateway
 LeaseTime
 DNS
 Destination IP address
255.255.255.255
(broadcast)
 Destination MAC
address of Client
(unicast)

19.  DHCPREQUEST message
 Destination IP address
255.255.255.255
(broadcast)
 Destination MAC address
of FF-FF-FF-FF-FF-FF
(broadcast)
 Source IP address of
0.0.0.0
 Way to inform other
DHCP Servers

20.  DHCPACKNOWLE
DGEMENT
 Destination IP
address
255.255.255.255
 Destination MAC
address of Client

22.  By default, lease period is limited to 8
days.
 Clients attempt to renew its lease as
50% of the lease duration has expired.

24.  If the client cannot find a DHCP
server then It may auto assign an IP
address from a reserved range
169.254.0.0 to 169.254.255.255 or
simply have an IP address of 0.0.0.0.

25.  ipconfig ./all -This command will show IP
and DNS settings
 ipconfig ./release -This command will
release the IP address from DHCP
 ipconfig ./renew -This command will renew
the IP address using DHCP

26. THANKS

27.  The IP address can either be permanent or
timed
 A permanent address is never reused for another
client
 Timed leases expire after a certain amount of
time
 Windows clients attempt to renew their lease
after 50% of the lease time has expired.
 A DHCP server may either honor or reject a
renew request

30.  If the client cannot find a DHCP
server then It may auto assign an IP
address from a reserved range
169.254.0.0 to 169.254.255.255 or
simply have an IP address of 0.0.0.0.

31.  Automatic Private IP Addressing (APIPA) is
a feature in operating systems (such as
Windows) that enables computers
to automatically self-configure an IP
address and subnet mask when
their DHCP server isn't reachable.The IP
address range for APIPA is 169.254

32.  (Automatic Private IP Addressing)The
Windows function that provides DHCP auto
configuration addressing. APIPA assigns a
class B IP address from 169.254. 0.0 to
169.254. 255.255 to the client when a DHCP
server is either permanently or temporarily
unavailable.

33.  When a DHCP client boots up, it looks for a
DHCP server in order to obtain network
parameters. If the client can’t communicate
with the DHCP server, it uses APIPA to
configure itself with an IP address from the
APIPA range.This way, the host will still be
able to communicate with other hosts on the
local network segment that are also
configured for APIPA.

34.  The APIPA service also checks regularly for
the presence of a DHCP server (every three
minutes). If it detects a DHCP server on the
network, the DHCP server replaces the APIPA
networking addresses with dynamically
assigned addresses.

35.  It relieves the network administrator of a great deal of manual
configuration work.
 The ability for a device to be moved from network to network
and to automatically obtain valid configuration parameters for
the current network can be of great benefit to mobile users.
 Because IP addresses are only allocated when clients are actually
active, it is possible, by the use of reasonably short lease times
and the fact that mobile clients do not need to be allocated more
than one address, to reduce the total number of addresses in use
in an organization.
 Centralized, simpler management of IP addressing:You can
manage IP addressing from a central location.
 Because the system assigns IP addresses, it leads to less
incorrect configurations of IP addresses.This is mainly due to IP
configuration information being entered at one location, and the
server distributing this information to clients.
 Duplicated IP addresses are prevented.
 IP addresses are also preserved.
 DHCP servers only allocate IP addresses to clients when they
request them.
 Dynamic IP addressing through DHCP easily scales from small
to large networking environments.

36.  The DHCP server can be a single point of failure in
networking environments that only have one DHCP
server.
 If your network has multiple segments, you have to
perform either of the following additional
configurations:
 Place a DHCP server on each segment
 Place a DHCP relay agent on each segment
 All incorrectly defined configuration information will
automatically be propagated to your DHCP clients.
 Uses UDP, an unreliable and insecure protocol.
 Potentially unauthorized clients
 Malicious client could exhaust address pool
 Malicious server (Rogue server)
 Supply incorrect configuration
parameters

37.  ipconfig ./all -This command will show IP
and DNS settings
 ipconfig ./release -This command will
release the IP address from DHCP
 ipconfig ./renew -This command will renew
the IP address using DHCP

38.  DNS stands for Domain Name System
 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.

39.  Users generally prefer names to numbers
 Computers prefer numbers to names
 DNS provides the mapping between the
name and numbers
 i.e. domain name to IP address

40.  In the Internet the domain name space is
divided into the Following sections:
 Generic Domains
 Country Domains

41.  The
generic
domains
define
registered
hosts
according
to their
generic
behavior.

42.  The country
domains
section uses
two-
character
country
abbreviations
 e.g., pk for
Pakistan

43.  Each name is made of several parts separated by dot (.)
 The first part can define the name of an organization.
 The second part can define the nature of the
organization. i.e. commercial, education, organization
etc.
 Some domain names have other parts like the starting
parts will define departments in the organization & the
ending parts will specify the country or sub type of
organization.
 E.g. www.yahoo.com
 For each new domain registartion, first it is check that
some one else don’t has domain name, if not then it is
registered.

44.  For simplicity the domain name is design
hierarchal as shown in figure.

45.  Forward Lookup Zones—Forward Lookup
Zones allow the DNS Server to resolve
queries where the client sends a name to
the DNS Server to request the IP address of
the requested host. Reverse Lookup Zones—
Reverse DNS zones perform the opposite
task as Forward Lookup Zones.

47.  On the Day of Judgment, no step shall a
man stir until he has answered questions
on five aspects of his worldly existence: His
life and how he spent it; his knowledge and
what use he made of it; his wealth—how he
acquired and spent it; and his body, and
how he utilized it.
 HADITH OF AT-TIRMIDI ONTHE AUTHORITYOF ABU
HURAYRAH

48.  How data / Information can be sent from source
to destination.
 Either source have single destination or multiple
destination.
 How data reach destination and router take
decision.
 We will study here
 Unicasting
 Multi casting
 Multiple casting
 Broadcasting

49. • In unicasting, there is one source and one
destination network.
• The relationship between the source and the
destination network is one to one.
• Each router in the path of the datagram tries
to forward the packet to one and only one of
its interfaces. (As Shown in the Figure).

50. • Figure shows a small internet
in which a unicast packet
needs to be delivered from a
source computer to a
destination computer
attached to N6.
• Router R1 is responsible to
forward the packet only
through interface 3; router
R4 is responsible to forward
the packet only through
interface 2. When the packet
arrives to N6,

52.  In multicasting, there is one source and a group
of destinations.
 The relationship is one to many.
 In this type of communication, the source
address is a unicast address, but the
destination address is a group address.

53.  In multicasting, a multicast router
may have to send out copies of the
same datagram through more than
one interface.
 In Figure 2, router R1 needs to send
out the datagram through
interfaces 2 and 3. Similarly, router
R4 needs to send out the datagram
through both its interfaces. Router
R3, however, knows that there is no
member belonging to this group in
the area reached by interface 2; it
only sends out the datagram
through interface 1.

55.  We need to distinguish between multicasting
and multiple unicasting.
 Figure 3 clarify both concepts.

57.  Multicasting = Single source multi destination but all will have single copy.
 Multiple Unicasting = Single source multi destination but one copy for each
destination separately.
 Multicasting starts with one single packet from the source that is duplicated by
the routers.
 Note that only one single copy of the packet travels between any two routers.
 In multiple unicasting, several packets start from the source. If there are four
destinations, for example, the source sends four packets, each with a different
unicast destination address.
 Note that there may be multiple copies traveling between two routers.
 For example, when a person sends an e-mail message to a group of people, this is
multiple unicasting.The e-mail software creates replicas of the message, each
with a different destination address, and sends them one by one.

58.  Multicasting is more efficient than multiple unicasting. In Figure 3, we
can see how multicasting requires less bandwidth than multiple
unicasting.
 In multiple unicasting, some of the links must handle several copies.
 In multiple unicasting, the packets are created by the source with a
relative delay between packets.
 If there are 1,000 destinations, the delay between the first and the last
packet may be unacceptable.
 In multicasting, there is no delay because only one packet is created by
the source.

59. 1. Information Spreading:
 Businesses often need to send information to their
customers. If the nature of the information is the
same for each customer, it can be multicast.
 In this way a business can send one message that
can reach many customers.
2. Spreading of News:
 In a similar manner news can be easily passed
around through multicasting.
 One single message can be sent to those interested
in a particular topic.

60. 3. Teleconferencing
 Teleconferencing involves multicasting.
 The individuals attending a teleconference all
need to receive the same information at the
same time.
4. Distance Learning
 One growing area in the use of multicasting is
distance learning.
 Lessons taught by one single professor can be
received by a specific group of students.

61.  In broadcast communication, the relationship
between the source and the destination is one to all.
 There is only one source, but all of the other hosts are
the destinations.
 The Internet does not support broadcasting because
of the huge amount of traffic it would create.
 Imagine the traffic generated in the Internet if one
person wanted to send a message to everyone else
connected to the Internet.

62.  In unicasting, the router forwards the received datagram through only
one of its interfaces.
 i.e. One Source One Destination
 In multicasting, a multicast router may have to send out copies of the
same datagram through more than one interface.
 i.e. One Source and Multi Destination.
 In multiple Unicasting, a single source having multiple destination but
each destination having separately copy.
 i.e. One Source and Multi Destination separate copy for each.
 In broadcast communication, the relationship between the source and
the destination is one to all.
 i.e. One Source and all destination

64.  The main difference between Ping and
Traceroute is that Ping is a quick and easy
utility to tell if the specified server is
reachable and how long will it take to send
and receive data from the server
whereas Traceroute finds the exact route
taken to reach the server and time taken by
each step (hop).