DHCP

1
DHCP

• MM Clements

2
Last Week

• Protocol architecture needed to contain a set of
  communication rules
• TCP/ IP dominates world communications
• SMTP, FTP TELNET all rely on TCP/ IP
• Port numbers are associated with application
  processes in Transport Layer
• IP addressing is dealt with in the Internet layer

3
This Week .

• Dynamic Host Configuration Protocol
• Automatic provision of information to clients at
  boot
• Comparison with BOOTP
• Sequence of operation
• Practical work

4
DHCP

• DHCP works by providing a process for a server to
  allocate the IP information to clients. Clients
  lease the information from the server for an
  administratively defined period.

5
BOOTP and DHCP Differences

• DHCP defines mechanisms through which clients can
  be assigned an IP address for a finite lease
  period.
• This lease period allows for re-assignment of the
  IP address to another client later, or for the
  client to get another assignment, if the client
  moves to another subnet.

6
DHCP vs. BOOTP

• Clients may also renew leases and keep the same
  IP address.
• DHCP provides the mechanism for a client to
  gather other IP configuration parameters, such as
  WINS and domain name.

7
Major DHCP Features

• Automatic Allocation
• Manual Allocation
• Dynamic Allocation

8
DHCP Operation
9
The Order of DHCP Message Transmission
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Packet Tracers DHCP server
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DHCP setup in PT 5.2

• Needs a pool name to identify the range
• Needs a default gateway
• Need DNS server IP address
• Needs the subnet mask
• Needs a start address
• Needs a total user number

12
PT 5.2 DHCP Interface

• Details of the LAN can be entered into the DHCP
  settings tab of Packet Tracer 5.2.

13
Domain Name System

• The domain name system uses a client/ server
  approach to the problem.
• Your computer sends a request to a domain name
  server
• What is the IP address for www.gre.ac.uk ?
• The server looks up the corresponding IP number
  and replies
• 193.60.68.107

14
Domain Name System

• Maps IP addresses to URLs
• Replaces original hosts.txt file (history)
• A-Record maps IP to URL
• Extra URLs can be mapped to original URL using
  CNAME (canonical name)
• System is used globally is open to abuse -
  beware

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Packet Tracers DNS tab
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More DNS next week
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Conclusion

• DHCP widely used
• Successor to BOOTP
• Provides basic IP addressing information to PCs
• Addresses leased from server
• Can be implemented on server or router