Network PPT- DHCP Fundamentals, components implementation and live analysis

 

 

Transcript

DHCP is an application layer protocol of the TCP/IP model.DHCP Server
Operating systems like Windows 2003, Windows 2008, Linux flavors , routers can be configured as DHCP Servers.
DHCP server is a configurable service on the above devices.
DHCP Client
Operating systems like Windows XP, Windows 7, Windows 2003 , Windows 2008, Linux devices, routers etc.
DHCP Client is configured on the network card.
DHCP stands for – Dynamic Host Configuration Protocol
DHCP is a client-server based architecture.
DHCP Client
DHCP Server
DHCP is used for receiving dynamic IP addresses on a network.
DHCP relieves the tedious process of configuring static IP addresses on the network
The DHCP Server is configured with a DHCP Scope
DHCP Scope contains the range of IP addresses which would be provided to the DHCP clients.
A typical scope would be between 192.168.1.1 – 192.168.1.254.
The scope would depend on the number of PC’s on the network considering expansion plans. The above scope would provide dynamic IP addresses for 254 devices.
Additional parameters like subnet mask, default gateway, dns server addresses are also provided in the scope which would be provided to the clients.
Application servers are typically configured with a static IP address.
Dynamic IP addresses are not recommended for application servers since application clients would not be aware of the same when there is a change in the IP address
DHCP communication consists of the following packets
DHCP Discover
This packet is sent from the DHCP client. This packet is sent with an intention to identify a DHCP server on the network. This is a broadcast packet
DHCP Offer
This packet is sent from the DHCP server to the DHCP client. The packet would contain the IP address and options like subnet mask, DNS IP address, gateway IP address and the IP address of the DHCP server providing the IP address
DHCP Request
The packet is sent from the client to the server
The packet informs the other DHCP servers on the network as to which IP address and the server the client has accepted.
DHCP Ack
The packet is sent from the server to the client
The packet acknowledges the request from the client.
The client confirms the acceptance of the received IP address
Live packet capture of DHCP packets between a client and a Server
DHCP Discover
Observe that the destination IP address is 255.255.255.255. This indicates that it is a broadcast
Observe the values in your IP address and Next server IP address fields. The values are 0.0.0.0. The client has not yet contacted a DHCP server or received an IP address
The client mac-address field is filled up the mac-address of the DHCP client initiating the packet
Observe the your IP address and Next Server IP address field values. The values are respectively the IP address (192.168.2.2) provided to the client in response to the DHCP Discover packet and the IP address of the server which has provided the IP address (192.168.2.1)
Observe the options field in the packet, It contains values for the IP address lease time , Domain Name, Domain Name Server, Subnet mask etc.
The transaction ID field and the DHCP server identifier is used to identify which DHCP servers request the client has accepted.
Observe that the packet is broadcast (Destination IP is 255.255.255.255). This is for other DHCP servers on the network to be informed that the client has accepted the IP address from the specific server mentioned in the DHCP Server identifier field
The transaction ID field and the DHCP server identifier is used to identify which DHCP servers request the client has accepted.
Observe that the packet is broadcast (Destination IP is 255.255.255.255). This is for other DHCP servers on the network to be informed that the client has accepted the IP address from the specific server mentioned in the DHCP Server identifier field

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