Dhcp presentation 01
- 1. DHCP …and how it works
- 2. Overview Introduction Basics Case - We play DHCP Server Problems Tasks Solutions Apply what you've learned Conclusion
- 3. Basics D ynamic H ost C onfiguration P rotocol Standard protocol Defined by RFC 1541 (superseded by RFC 2131) Created by the Host Configuration Working Group of the I nternet E ngineering T ask F orce (IETF)
- 4. 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. 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. Case - Theory 1 st 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. 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. 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. 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. 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. Case - Theory Static/Manual allocation Server allocates IP chosen by the Admin Server configuration includes IP-Address -and- MAC-Address for every client DHCP only used to convey assigned address to client
- 12. 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 clients end
- 13. 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. 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. Case - Theory By 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. 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. 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. 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. Conclusion Thank you for your attention …any questions??
- 20. Refrences RFC 2131, Dynamic Host Configuration Protocol RFC 2322, Management of IP numbers by peg-dhcp www.ietf.org , I nternet E ngineering T ask F orce www.microsoft.com , Microsoft Knowledge Base Article - 169289
Editor's Notes
- #8: a peg is a 'token' and represents one IP-number, therefore making the status of the IP-number (allocated or not allocated) visible