\begin{ucsTabbox}{'[DHCP Allow/Deny]' tab}
\ucsNote{The keyword \ucsMenuEntry{ignore} used in the tab is only
  different from \ucsMenuEntry{deny} in that it prohibits the
  logging of denied requests.} 

\ucsTabentry{Unknown clients}
If \ucsMenuEntry{allow} is selected from the list, the DHCP service
also issues IP addresses to clients which do not have a DHCP computer
entry. If on the other hand \ucsMenuEntry{deny} or
\ucsMenuEntry{ignore} is selected, the DHCP service does not issue IP
addresses to unknown clients.

It is recommended not to perform this setting globally or on the
subnet level, but rather at the pool level. (see \ucsMenuEntry{Advanced}
tab in DHCP:Pool objects on page
\pageref{module:dhcp:pool-objekt-karteikarte-fortgeschritten}).

\ucsTabentry{BOOTP}
When nothing or \ucsMenuEntry{allow} is selected from the list, the
DHCP replies to BOOTP requests, otherwise it does not reply to these
requests.

\ucsTabentry{Booting}
This input stipulates whether requests (from a particular client) are
replied to (no selection or \ucsMenuEntry{allow}) or not
(\ucsMenuEntry{deny} or \ucsMenuEntry{ignore} selected) by the DHCP
service. If the DHCP service does not reply, the client is not
assigned an IP address. The setting is usually only made directly for
a DHCP computer object.

\ucsTabentry{Duplicates}
When nothing or \ucsMenuEntry{allow} is selected in this list, the
DHCP service allows clients to receive a new lease and keep existing
leases which belong to the same MAC address.

If the entry \ucsMenuEntry{deny} is used and the MAC address of the
client submitting the request matches a DCP computer entry, the DHCP
discards all leases which match the same MAC address. This action is a
breach of the DHCP protocol, but can avoid the case of clients with a
client identifier which changes often receiving many leases at the
same time.

\ucsTabentry{Declines}
If nothing or \ucsMenuEntry{allow} is selected in the list, the DHCP
service accepts \emph{DHCPDECLINE} messages from the client. The
client sends these messages when it deems the proffered IP address
invalid. The DHCP service then gives this IP address the status
\emph{abandoned} and does not use it for a certain period of time. A
defective or malicious client can exhaust the pool of free addresses
by sending \emph{DHCPDECLINE} messages excessively. If
\ucsMenuEntry{deny} or \ucsMenuEntry{ignore} is selected, the DHCP
service ignores these messages.
\end{ucsTabbox}
