The process of starting a computer system is known as bootstrapping.

1. Presented By
===========
Ashish Malik
M.Tech - Information Security & Computer Forensics (SRM University)

2.  The process of starting a computer system is
known as bootstrapping.
 The sequence begins with code in ROM
 It loads an image in RAM
 Two approaches to obtain an image :
 Embedded System
▪ ROM code use n/w support to locate & download image.
 Conventional Computer
▪ ROM code loads image from well-known place on disk.

3.  Loaded image is not configured according to
the specific physical hardware.
 It does not contain any networking details.
 Early implementation of TCP/IP provided
separate mechanism to obtain configuration
information e.g. RARP to obtain IP address.
 When subnet masks were introduced, ICMP
address mask message were added to obtain
a subnet mask.

4.  Advantage
 Flexibility
 Computer decides which item to obtain from local
disk and which to obtain over the n/w.
 Disadvantage
 Network traffic and delay
 Computer issues request messages to server. Each
response returns a small value (IP). Networks
enforce min. packet size, so most of the space in
each packet is wasted.

5.  It was invented to supply more than one item
of configuration information in a single step.
 BOOTP server provide several pieces of
information at once like :
 Computers IP address
 Server’s name and IP address
 IP address of a default router
 BOOTP uses IP to send request and receive
response.

6.  How BOOTP uses Unconfigured IP ?
 It’s design allow IP to broadcast an IP
datagram request before all values have been
configured.
 Destination address used : all 1’s
 Source address used : all 0’s
 BOOTP responds either via broadcast
message or via MAC address.

7.  BOOTP uses UDP so messages can be
delayed, lost or duplicated.
 BOOTP requires that UDP use checksums.
 To handle datagram loss, BOOTP uses
technique of timeout & retransmission.

9.  BOOTP uses a two-step bootstrap procedure:
▪ It only provides client with the information needed to
obtain an image.
▪ Client then uses TFTP to obtain the image.
 BOOTP was designed for a static environment.
 With advent of networking and portable
PC’s, BOOTP does not adapt to such situations as
info. can not be exchanged quickly.
 Hence we needed another protocol, DHCP.

10.  Dynamic Host Configuration Protocol
 It was devised to automate the configuration.
 It use plug-and-play networking to join a new
network and obtain an IP address.
 DHCP server can be configured to have two
type of addresses :
 Permanent addresses
▪ Assigned to server computers.
 Pool of addresses
▪ These are to be allocated on demand.

11.  Addresses assigned on demand are not
permanent.
 DHCP issues a lease on the address for a
finite period of time.
 If lease expires, computer must renegotiate
with the DHCP server.
 If an event cause all computers to restart at
same time, DHCP uses the same technique as
BOOTP to avoid flooding with requests.
 i.e. waiting for a random amount of time.

13.  This protocol has two steps :
 Broadcast DHCP discover message
 Send request to server that responded
 To avoid repeating above steps, DHCP uses
caching.

15. Thank You