2. 2
introduction
The information that is held in each computer attached
to a TCP/IP internet:
Its IP address
Its subnet mask
The IP address of a router
The IP address of a name server
The above information is usually stored in a
configuration file and accessed by the computer during the
bootstrap process
In the case of a diskless computer, the operating system
and networking can be stored in ROM. But the above
information cannot be stored in ROM.
3. BOOTP
BOOTP(Bootstrap Protocol) is client/server protocol
designed to provide the information for a diskless computer
or a computer that is booted for the first time
RARP provides only the IP address and not the other
information
If we use BOOTP, we do not need RARP.
BOOTP is static.When a client workstation asks for the
above info, it is retrieved from a fixed table. Every time the
client asks for the info, it gets the same results.
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4. BOOTP
UDP Ports
BOOTP is the client’s use of the well-known port 68
if two hosts with same well-known port 68 use BOOTP at the same
time in case of broadcasting the reply, both hosts receive the
message. In this case, transaction ID is used
Using TFTP
If a client needs more information for booting, the client can use the
pathname of a file sent by server which the client can find complete
booting information.
The client can then use a TFTP message to get the rest of the
needed information.
TCP/IP Protocol Suite 4
5. 5
Figure 1 Client and server on the same network
BOOTP places its packet inside a UDP packet (note that BOOTP
is an application layer program).
6. Operation
Steps involved in use of
the BOOTP protocol
1) BOOTP server uses UDP port 67
and waiting for a client
2) The client sends a BOOTP request
message to the server. The client uses
(0s )as the source address and all( 1s)
as the destination address.
3) The server replies to the client with
Either a broadcast or a unicast message
using UDP destination port 68.
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7. 7
Figure 2 Client and server on two different networks
When client and server are on different networks, we need a
relay agent, because client does not know IP address of
server,. Relay agent knows the IP addr of the server.
9. Bootp Format
• Operation code : request(1) or reply (0)
• Transaction ID : set by the client and used to match a reply
with the request
• Number of seconds : indicating the number of seconds
elapsed since the time the client started to boot
• Your IP address : client address filled by server (in the
client message)
• Server IP address : in a reply message
• Gateway IP address : IP address of a router in a reply
message.
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10. Bootp Format
• Server name : the domain name of the server in a reply
packet
• Boot filename : the full pathname of the boot in a reply
packet (128-byte)
• Options : used in a reply message (64-byte)
carrying either additional information (such as the
network mask or default router address) or some
specific information
in case of magic cookie, options have following options.
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