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DHCP. DHCP. Dynamic Host Configuration Protocol (DHCP) From 1993 An extension of BOOTP, very similar to DHCP Same port numbers as BOOTP DHCP is the preferred mechanism for dynamic assignment of IP addresses DHCP can interoperate with BOOTP clients. DHCP. - PowerPoint PPT Presentation
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DHCP
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DHCP
• Dynamic Host Configuration Protocol (DHCP) • From 1993• An extension of BOOTP, very similar to DHCP• Same port numbers as BOOTP
• DHCP is the preferred mechanism for dynamic assignment of IP addresses
• DHCP can interoperate with BOOTP clients.
DHCP
• Dynamic Host Configuration Protocol
• It is a method for assigning Internet Protocol (IP) addresses permanently or to individual computers in an organization’s network
• DHCP lets a network administrator supervise and distribute IP addresses from a central point and automatically sends a new IP address when a computer is plugged into a different place in the network
MOTIVATION FOR DHCP
• Static Vs Dynamic IP
• Configuration parameters for network hostsIP addressRouterSubnet MaskOthers..
DYNAMIC HOST CONFIGURATION PROTOCOL (DHCP)
• Four Key benefits to DHCP:• Centralized administration of IP configuration.• Dynamic host configuration.• Seamless IP host configuration.• Flexibility and scalability.
DISADVANTAGES OF DHCP
• When DHCP server is unavailable, client is unable to access enterprises network
• Your machine name does not change when you get a new IP address
• Uses UDP, an unreliable and insecure protocol.
• DNS cannot be used for DHCP configured hosts.
SECURITY PROBLEM
• DHCP is an unauthenticated protocolWhen connecting to a network, the user is not
required to provide credentials in order to obtain a lease
Malicious users with physical access to the DHCP-enabled network can instigate a denial-of-service attack on DHCP servers by requesting many leases from the server, thereby depleting the number of leases that are available to other DHCP clients
LIMITATIONS
• Some machines on your network need to be at fixed addresses, for example servers and routers
• You need to be able to assign a machine to run the DHCP server continually as it must be available at all times when clients need IP access
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DHCP INTERACTION (SIMPLIFIED)Argon
00:a0:24:71:e4:44 DHCP Server
DHCP Request00:a0:24:71:e4:44Sent to 255.255.255.255
Argon128.143.137.14400:a0:24:71:e4:44 DHCP Server
DHCP Response:IP address: 128.143.137.144Default gateway: 128.143.137.1Netmask: 255.255.0.0
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DHCP OPERATIONDHCP Client
00:a0:24:71:e4:44 DHCP Server
DHCPDISCOVERSent to 255.255.255.255
DHCP Server
• DCHP DISCOVER
DHCP Client00:a0:24:71:e4:44 DHCP Server
DHCP Server
DHCPOFFER
DHCPOFFERDCHP OFFER
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DHCP OPERATIONDHCP Client
00:a0:24:71:e4:44 DHCP Server
DHCP Server
DHCPREQUEST
DHCPACKDCHP DISCOVER
At this time, the DHCP client can start to use the IP address
DHCP Client00:a0:24:71:e4:44 DHCP Server
DHCP Server
DHCPREQUEST
DHCPACKRenewing a Lease(sent when 50% of lease
has expired)If DHCP server sends DHCPNACK, then address is released.
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DHCP OPERATIONDHCP Client
00:a0:24:71:e4:44 DHCP Server
DHCP Server
DHCPRELEASE
DCHP RELEASE
At this time, the DHCP client has released the IP address
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BOOTP/DHCP MESSAGE FORMAT
Number of Seconds
OpCode (1 = Req, 2 = Reply)
Hardware Type (1 = Ethernet)
Your IP address
Unused (in BOOTP)Flags (in DHCP)
Gateway IP address
Client IP address
Server IP address
Hardware Address Length Hop Count
Server host name (64 bytes)
Client hardware address (16 bytes)
Boot file name (128 bytes)
Transaction ID
Options
(There are >100 different options)
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DHCP MESSAGE TYPE• Message type is sent as an
option. Value Message Type
1 DHCPDISCOVER
2 DHCPOFFER
3 DHCPREQUEST
4 DHCPDECLINE
5 DHCPACK
6 DHCPNAK
7 DHCPRELEASE
8 DHCPINFORM
