1 DHCP

MADE BY: VIPAL PATEL

130410107080SY CE-2

DHCP…and how it works

2 DHCP Overview

Overview• Introduction• Basics• Case - We play DHCP Server

• Problems • Tasks• Solutions• Apply what you've learned

• Conclusion

3 DHCP in general

Basics• Dynamic Host Configuration Protocol• Standard protocol• Defined by RFC 1541 (superseded by

RFC 2131)• Created by the

Host Configuration Working Group of the Internet Engineering Task Force (IETF)

4 DHCP techiques

Basics• Runs over UDP• Utilizing ports:

• 67 – connections to server• 68 – connections to client

• Extension of BOOTP (protocol used for simple interaction)

• Uses client–server model

5 DHCP problem

Case• Got a network• Want to add new clients• DHCP-Server doesn’t work• How do clients get their:

• IP Address -or- • network configuration parameters (Subnet

Mask, Default Gateway, DNS and WINS)• Need replacement!!

6 DHCP server tasks I

Case - Theory1st implementation goal of a DHCP

Server• support of dynamic allocation of

Network Addresses • chooses and allocates an IP address • gives network configuration parameters

to the client

7 DHCP parts of a DHCP Server

Case - Theory• Need 2 databases

• Address Pool is the database which holds IP addresses and other network configuration parameters

• Binding database keeps mapping between an Ethernet address and Address Pool entries

8 DHCP client conditions

Case - Theory• All interactions are initiated by a

client• Server only replies• “obtain an IP address automatically”

in NW options• configuring the host to the network is

done by a simple handshake

9 DHCP steps in becoming part of the network I

Case – in practice• Client broadcasts DHCPDISCOVER • One or more servers return DHCPOFFER

with available Address and NW Information

• Clients chooses one offer that it likes best

• broadcasts DHCPREQUEST to identify chosen Server/lease

• DHCPREQUEST also to renew lease

10 DHCP steps in becoming part of the network II

Case - in practice• Server sends

• DHCPACK• Lease is finalized• Client starts using IP

• DHCPNAK• Client resumes from DHCPDISCOVER point

• If client doesn’t want IP - DHCPDECLINE is sent

• DHCPRELEASE gives IP back into pool

11 DHCP types of assigning addresses I

Case - Theory• Static/Manual allocation

• Server allocates IP chosen by the Admin• Server configuration includes

• IP-Address -and-• MAC-Addressfor every client

• DHCP only used to convey assigned address to client

12 DHCP types of assigning addresses II

Case - Theory• Automatic allocation

• IP address is permanently associated with a MAC address

• till administrator intervenes the infinite lease

• Dynamic allocation• Like Automatic allocation• Except:

• server tracks leases• give IP addresses whose lease has expired to

other DHCP clientsend

13 DHCP lease duration

Case - Theory• Client is responsible to renew/release IP• Lease timestamps:

• Total lease duration • T1 (0.5 * duration_of_lease)

• client enters the RENEWING state • contacts the server that originally issued

network address• T2 (0.875 * duration_of_lease)

• client enters the REBINDING state • attempts to contact any server

14 DHCP problems

Case - Theory• Lease duration

• Client holds IP when not connected• Clients retire• Servers/Databases should have constant

IP´s• Analyze the NW

• Often changing clients?• Servers/databases?• Enough IP Addresses available?

15 DHCP server tasks II

Case - TheoryBy using the fitting Methods…implementation goals 2-4 of a DHCP Server…

• server should be able to recycle the IP address when the lease period is expired

• A network administrator should not configure each client/user interaction of each client should not be required.

• support of static allocation and an infinite lease

…can also be realized!!!!

16 DHCP find a solution!!!

Case - in practice• Servers:

• WEB-Server 192.168.1.1• Access Point 192.168.1.2

• Lecturers via Ethernet:• Range from .100 to .102

• Students via WLAN:• Range from .200 to .230

back

17 DHCP negative aspects

Conclusion• Insecurity of UDP• Broadcast of messages• Risk of wrong configuration causing

• High traffic• Waste of IP Addresses• A lot more work than expected

• Detailed and precise analysis before implementation needed

18 DHCP positive aspects

Conclusion• works well if you have to manage a lot of

mobile users: • people with laptops working in and out of the office• hosts coming and going with a great amount of

frequency• perfect when Network parameters have

changed• only one point you have to work at

• sharing a limited pool of IP addresses • Mixture of allocation types can be used

19 DHCP the end

Conclusion

Thank you

20 DHCP

Refrences• RFC 2131, Dynamic Host

Configuration Protocol• RFC 2322, Management of IP

numbers by peg-dhcp • www.ietf.org, Internet Engineering

Task Force • www.microsoft.com, Microsoft

Knowledge Base Article - 169289