Update of /cvsroot/dhcp-agent/dhcp-agent/doc
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introduction.texi
Log Message:
added write up on DHCP
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inaccuracy when calculating timeouts. Lobby your OpenBSD developers to
stop the brain damage.
+
+ @section Overview of DHCP
+
+ DHCP (Dynamic Host Configuration Protocol) is a protocol designed to
+ assign host configuration parameters from a DHCP server to a DHCP
+ client. The parameters are passed as a lease to the client. The term
+ lease is used because the parameters usually have a finite
+ lifetime. This allows the network administrator to update the
+ configuration parameters, and later propogate the configuration
+ changes to the client hosts.
+
+ DHCP is a convenient method of maintaining configuration across
+ multiple machines from a central configuration repository.
+
+ @subsection Lease Acquisition
+
+ The client begins by broadcasting a DHCP DISCOVER message, which
+ solicits DHCP leases from servers.
+
+ DHCP OFFER messages are sent from DHCP servers to the client.
+
+ The client picks one of the lease offers and responds with a DHCP
+ REQUEST. The server responds with a DHCP ACK to acknowledge, or
+ DHCP NACK to refuse assigning the lease.
+
+ Once the client receives the acknowledgement it checks to see if the
+ IP address is currently active. If no address collision is detected,
+ the client performs its configuration based on the address passed from
+ the server and additional options provided in the lease.
+
+ If address collision is detected, the client transmits a DHCP DECLINE
+ message informing the server that the lease is no good.
+
+ @subsection Lease Renewal
+
+ Each lease comes with three timers, a rebind, renew, and an expiry
+ timer. If no rebind or renew time is specified the client can create
+ default rebind and renew timers from the expiry time.
+
+ When these timers are reached the client attempts to renew the lease
+ by transmitting a DHCP REQUEST and awaiting an acknowledgement. If the
+ timer expires and the lease is not renewed, the client undoes the
+ system configuration and revers to its lease acquisition stage.
+
+ @subsection Lease Release
+
+ When the client is shut down it sends a DHCP RELEASE message to the
+ server notifying it that the lease is no longer in use. The client,
+ also, unconfigures the host system its running on.
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