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.
8.
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.
12.
13. This protocol has two steps :
Broadcast DHCP discover message
Send request to server that responded
To avoid repeating above steps, DHCP uses
caching.