DHCP

-DHCP is Dynamic Host Configuration Protocol.

-DHCP is a protocol (of OSI application layer).


-Definition: DHCP delivers IP addresses to hosts within a network.

With DHCP, each computer connected to the network receives quickly and automatically an IP address, and this address is unique.


-DHCP is described in RFC 2131.


-A DHCP server uses DHCP protocol.


-DHCP uses Discover Offer Request Acknowledgement (DORA).


-Examples of DHCP servers:
*Windows Server 2003 can be a DHCP server
*Windows Server 2012 can be a DHCP server
*Windows Server 2016 can be a DHCP server
*A router can be a DHCP server. A router can also be a DHCP relay agent.
*Your Internet Access Provider's BOX can be a DHCP server.


-A DHCP server must have a static IP address.


-DHCP uses UDP (User Datagram Protocol).
It's on port 68 for the clients and on port 67 for the servers.


-In Active Directory, there is ENTERPRISE ADMINISTRATORS group.
A user must be a member of this group to be able to modify the DHCP configuration.


-The DHCP Range is also called DHCP Scope: it is the list of the IP addresses for assignment to hosts.


-DHCP lease time
Definition: it is the time duration that a computer will keep the same IP address.

Examples:
DHCP lease time= 15 min;
DHCP lease time= 24h;
DHCP lease time= 8 days;
DHCP lease time= 4 months;
DHCP lease time= 1 year;
DHCP lease time= infinite.


-The following DOS command cleans the DHCP configuration:
ipconfig /release

-The following DOS command asks to receive a new DHCP configuration:
ipconfig /renew

-Verification: ipconfig /all


-If the DHCP server is unavailable, then the hosts will receive the IP addresses like 169.254.X.X


-IPv4 and IPv6 need DHCP


-DHCP server can provide an IP address to the DNS server


-What is APIPA (created by Microsoft)?
If a DHCP server failed to provide IP addresses to hosts, then APIPA will generate the missing IP addresses and get then to the relevant machines.


-A Cisco router can be a DHCP server, you can write the following commands:
enable
configuration terminal
ip dhcp pool cisco
network writetheipaddress writethemask
default-router writetheipaddress
ip dhcp excluded-address writetheipaddresstobeexcludedasgatewayandrouter


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