DHCP …and how it works
Overview <ul><li>Introduction </li></ul><ul><li>Basics </li></ul><ul><li>Case - We play DHCP Server </li></ul><ul><ul><li>...
Basics <ul><li>D ynamic  H ost  C onfiguration  P rotocol </li></ul><ul><li>Standard protocol </li></ul><ul><li>Defined by...
Basics <ul><li>Runs over UDP </li></ul><ul><li>Utilizing ports: </li></ul><ul><ul><li>67 – connections to server </li></ul...
Case <ul><li>Got a network </li></ul><ul><li>Want to add new clients </li></ul><ul><li>DHCP-Server doesn’t work </li></ul>...
Case - Theory <ul><li>1 st  implementation goal of a DHCP Server </li></ul><ul><li>support of dynamic allocation of Networ...
Case - Theory <ul><li>Need 2 databases </li></ul><ul><ul><li>Address Pool  is the database which holds IP addresses and ot...
Case - Theory <ul><li>All interactions are initiated by a client </li></ul><ul><li>Server only replies </li></ul><ul><li>“...
Case – in practice <ul><li>Client broadcasts DHCPDISCOVER  </li></ul><ul><li>One or more servers return DHCPOFFER with ava...
Case - in practice <ul><li>Server sends </li></ul><ul><ul><li>DHCPACK </li></ul></ul><ul><ul><ul><li>Lease is finalized </...
Case - Theory <ul><li>Static/Manual allocation   </li></ul><ul><ul><li>Server allocates IP chosen by the Admin </li></ul><...
Case - Theory <ul><li>Automatic allocation </li></ul><ul><ul><li>IP address is permanently associated with a MAC address <...
Case - Theory <ul><li>Client is responsible to renew/release IP </li></ul><ul><li>Lease timestamps: </li></ul><ul><ul><li>...
Case - Theory <ul><li>Lease duration </li></ul><ul><ul><li>Client holds IP when not connected </li></ul></ul><ul><ul><li>C...
Case - Theory <ul><li>By using the fitting Methods… </li></ul><ul><li>implementation goals 2-4 of a DHCP Server… </li></ul...
Case - in practice <ul><li>Servers: </li></ul><ul><ul><li>WEB-Server 192.168.1.1 </li></ul></ul><ul><ul><li>Access Point 1...
Conclusion <ul><li>Insecurity of UDP </li></ul><ul><li>Broadcast of messages </li></ul><ul><li>Risk of wrong configuration...
Conclusion <ul><li>works well if you have to manage a lot of mobile users:  </li></ul><ul><ul><li>people with laptops work...
Conclusion <ul><li>Thank you for your attention </li></ul><ul><li>  </li></ul><ul><li> …any questions?? </li></ul>
Refrences <ul><li>RFC 2131,  Dynamic Host Configuration Protocol </li></ul><ul><li>RFC 2322, Management of IP numbers by p...
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Dhcp presentation 01

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  • a peg is a &apos;token&apos; and represents one IP-number, therefore making the status of the IP-number (allocated or not allocated) visible
  • Dhcp presentation 01

    1. 1. DHCP …and how it works
    2. 2. Overview <ul><li>Introduction </li></ul><ul><li>Basics </li></ul><ul><li>Case - We play DHCP Server </li></ul><ul><ul><li>Problems </li></ul></ul><ul><ul><li>Tasks </li></ul></ul><ul><ul><li>Solutions </li></ul></ul><ul><ul><li>Apply what you've learned </li></ul></ul><ul><li>Conclusion </li></ul>
    3. 3. Basics <ul><li>D ynamic H ost C onfiguration P rotocol </li></ul><ul><li>Standard protocol </li></ul><ul><li>Defined by RFC 1541 (superseded by RFC 2131) </li></ul><ul><li>Created by the </li></ul><ul><li>Host Configuration Working Group </li></ul><ul><li>of the </li></ul><ul><li>I nternet E ngineering T ask F orce (IETF) </li></ul>
    4. 4. Basics <ul><li>Runs over UDP </li></ul><ul><li>Utilizing ports: </li></ul><ul><ul><li>67 – connections to server </li></ul></ul><ul><ul><li>68 – connections to client </li></ul></ul><ul><li>Extension of BOOTP (protocol used for simple interaction) </li></ul><ul><li>Uses client–server model </li></ul>
    5. 5. Case <ul><li>Got a network </li></ul><ul><li>Want to add new clients </li></ul><ul><li>DHCP-Server doesn’t work </li></ul><ul><li>How do clients get their: </li></ul><ul><ul><li>IP Address -or- </li></ul></ul><ul><ul><li>network configuration parameters (Subnet Mask, Default Gateway, DNS and WINS) </li></ul></ul><ul><li>Need replacement!! </li></ul>
    6. 6. Case - Theory <ul><li>1 st implementation goal of a DHCP Server </li></ul><ul><li>support of dynamic allocation of Network Addresses </li></ul><ul><ul><li>chooses and allocates an IP address </li></ul></ul><ul><ul><li>gives network configuration parameters to the client </li></ul></ul>
    7. 7. Case - Theory <ul><li>Need 2 databases </li></ul><ul><ul><li>Address Pool is the database which holds IP addresses and other network configuration parameters </li></ul></ul><ul><ul><li>Binding database keeps mapping between an Ethernet address and Address Pool entries </li></ul></ul>
    8. 8. Case - Theory <ul><li>All interactions are initiated by a client </li></ul><ul><li>Server only replies </li></ul><ul><li>“obtain an IP address automatically” in NW options </li></ul><ul><li>configuring the host to the network is done by a simple handshake </li></ul>
    9. 9. Case – in practice <ul><li>Client broadcasts DHCPDISCOVER </li></ul><ul><li>One or more servers return DHCPOFFER with available Address and NW Information </li></ul><ul><li>Clients chooses one offer that it likes best </li></ul><ul><li>broadcasts DHCPREQUEST to identify chosen Server/lease </li></ul><ul><li>DHCPREQUEST also to renew lease </li></ul>
    10. 10. Case - in practice <ul><li>Server sends </li></ul><ul><ul><li>DHCPACK </li></ul></ul><ul><ul><ul><li>Lease is finalized </li></ul></ul></ul><ul><ul><ul><li>Client starts using IP </li></ul></ul></ul><ul><ul><li>DHCPNAK </li></ul></ul><ul><ul><ul><li>Client resumes from DHCPDISCOVER point </li></ul></ul></ul><ul><li>If client doesn’t want IP - DHCPDECLINE is sent </li></ul><ul><li>DHCPRELEASE gives IP back into pool </li></ul>
    11. 11. Case - Theory <ul><li>Static/Manual allocation </li></ul><ul><ul><li>Server allocates IP chosen by the Admin </li></ul></ul><ul><ul><li>Server configuration includes </li></ul></ul><ul><ul><ul><li>IP-Address -and- </li></ul></ul></ul><ul><ul><ul><li>MAC-Address </li></ul></ul></ul><ul><ul><ul><li>for every client </li></ul></ul></ul><ul><ul><li>DHCP only used to convey assigned address to client </li></ul></ul>
    12. 12. Case - Theory <ul><li>Automatic allocation </li></ul><ul><ul><li>IP address is permanently associated with a MAC address </li></ul></ul><ul><ul><li>till administrator intervenes the infinite lease </li></ul></ul><ul><li>Dynamic allocation </li></ul><ul><ul><li>Like Automatic allocation </li></ul></ul><ul><ul><li>Except: </li></ul></ul><ul><ul><ul><li>server tracks leases </li></ul></ul></ul><ul><ul><ul><li>give IP addresses whose lease has expired to other DHCP clients </li></ul></ul></ul>end
    13. 13. Case - Theory <ul><li>Client is responsible to renew/release IP </li></ul><ul><li>Lease timestamps: </li></ul><ul><ul><li>Total lease duration </li></ul></ul><ul><ul><li>T1 (0.5 * duration_of_lease) </li></ul></ul><ul><ul><ul><li>client enters the RENEWING state </li></ul></ul></ul><ul><ul><ul><li>contacts the server that originally issued network address </li></ul></ul></ul><ul><ul><li>T2 (0.875 * duration_of_lease) </li></ul></ul><ul><ul><ul><li>client enters the REBINDING state </li></ul></ul></ul><ul><ul><ul><li>attempts to contact any server </li></ul></ul></ul>
    14. 14. Case - Theory <ul><li>Lease duration </li></ul><ul><ul><li>Client holds IP when not connected </li></ul></ul><ul><ul><li>Clients retire </li></ul></ul><ul><ul><li>Servers/Databases should have constant IP´s </li></ul></ul><ul><li>Analyze the NW </li></ul><ul><ul><li>Often changing clients? </li></ul></ul><ul><ul><li>Servers/databases? </li></ul></ul><ul><ul><li>Enough IP Addresses available? </li></ul></ul>
    15. 15. Case - Theory <ul><li>By using the fitting Methods… </li></ul><ul><li>implementation goals 2-4 of a DHCP Server… </li></ul><ul><ul><li>server should be able to recycle the IP address when the lease period is expired </li></ul></ul><ul><ul><li>A network administrator should not configure each client/user interaction of each client should not be required. </li></ul></ul><ul><ul><li>support of static allocation and an infinite lease </li></ul></ul><ul><li>… can also be realized!!!! </li></ul>
    16. 16. Case - in practice <ul><li>Servers: </li></ul><ul><ul><li>WEB-Server 192.168.1.1 </li></ul></ul><ul><ul><li>Access Point 192.168.1.2 </li></ul></ul><ul><li>Lecturers via Ethernet: </li></ul><ul><ul><li>Range from .100 to .102 </li></ul></ul><ul><li>Students via WLAN: </li></ul><ul><ul><li>Range from .200 to .230 </li></ul></ul>back
    17. 17. Conclusion <ul><li>Insecurity of UDP </li></ul><ul><li>Broadcast of messages </li></ul><ul><li>Risk of wrong configuration causing </li></ul><ul><ul><li>High traffic </li></ul></ul><ul><ul><li>Waste of IP Addresses </li></ul></ul><ul><ul><li>A lot more work than expected </li></ul></ul><ul><li>Detailed and precise analysis before implementation needed </li></ul>
    18. 18. Conclusion <ul><li>works well if you have to manage a lot of mobile users: </li></ul><ul><ul><li>people with laptops working in and out of the office </li></ul></ul><ul><ul><li>hosts coming and going with a great amount of frequency </li></ul></ul><ul><li>perfect when Network parameters have changed </li></ul><ul><ul><li>only one point you have to work at </li></ul></ul><ul><li>sharing a limited pool of IP addresses </li></ul><ul><li>Mixture of allocation types can be used </li></ul>
    19. 19. Conclusion <ul><li>Thank you for your attention </li></ul><ul><li> </li></ul><ul><li> …any questions?? </li></ul>
    20. 20. Refrences <ul><li>RFC 2131, Dynamic Host Configuration Protocol </li></ul><ul><li>RFC 2322, Management of IP numbers by peg-dhcp </li></ul><ul><li>www.ietf.org , I nternet E ngineering T ask F orce </li></ul><ul><li>www.microsoft.com , Microsoft Knowledge Base Article - 169289 </li></ul>

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