201 lines
3.3 KiB
HTML
201 lines
3.3 KiB
HTML
<HTML
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><HEAD
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><TITLE
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>Obey Data Terminal Ready and Data Carrier Detect</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
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REL="HOME"
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TITLE="Remote Serial Console HOWTO"
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HREF="index.html"><LINK
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REL="UP"
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TITLE="Security"
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HREF="security.html"><LINK
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REL="PREVIOUS"
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TITLE="Use good passwords"
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HREF="security-password.html"><LINK
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REL="NEXT"
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TITLE="Use or configure a dumb modem"
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HREF="security-dumb.html"></HEAD
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><BODY
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CLASS="SECTION"
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BGCOLOR="#FFFFFF"
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TEXT="#000000"
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LINK="#0000FF"
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VLINK="#840084"
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ALINK="#0000FF"
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><DIV
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CLASS="NAVHEADER"
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><TABLE
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SUMMARY="Header navigation table"
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WIDTH="100%"
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BORDER="0"
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CELLPADDING="0"
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CELLSPACING="0"
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>Remote Serial Console HOWTO</TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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><A
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HREF="security-password.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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>Chapter 9. Security</TD
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><TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="security-dumb.html"
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ACCESSKEY="N"
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>Next</A
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></TD
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></TR
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><DIV
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CLASS="SECTION"
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><H1
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CLASS="SECTION"
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><A
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NAME="SECURITY-DTR"
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></A
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>9.2. Obey Data Terminal Ready and Data Carrier Detect</H1
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><P
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>The <SPAN
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CLASS="ACRONYM"
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>RS-232</SPAN
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> Data Terminal Ready signal is
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lowered when the computer wishes the modem to hang up. The
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computer wishes to hang up when people have ended their login
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session ends or when they fail to respond to the
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<TT
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CLASS="PROMPT"
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>login:</TT
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> prompt.</P
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><P
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>Using a modem cable that has <SPAN
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CLASS="ACRONYM"
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>DTR</SPAN
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> wired and a
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modem that is configured to obey <SPAN
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CLASS="ACRONYM"
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>DTR</SPAN
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> is essential
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to prevent denial of service attacks upon the access to the
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console.</P
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><P
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>Without <SPAN
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CLASS="ACRONYM"
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>DTR</SPAN
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> a caller can simply hold the
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modem line open, denying system administrators access to the
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console.</P
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><P
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>The <SPAN
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CLASS="ACRONYM"
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>RS-232</SPAN
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> Data Carrier Detect signal is
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lowered when the user hangs up.</P
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><P
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>Using a modem cable that has <SPAN
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CLASS="ACRONYM"
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>DCD</SPAN
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> wired and
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a modem that is configured to assert <SPAN
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CLASS="ACRONYM"
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>DCD</SPAN
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> is
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essential to prevent people dialling in after a user has hang up
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and from carrying on their session.</P
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><P
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>Without <SPAN
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CLASS="ACRONYM"
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>DCD</SPAN
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> the session is not cleared when
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an accidental disconnection occurs. This allows any subsequent
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caller to resume the previous session. The machine is totally
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compromised if the previous user was <SPAN
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CLASS="SYSTEMITEM"
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>root</SPAN
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>.</P
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></DIV
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><DIV
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CLASS="NAVFOOTER"
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><HR
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ALIGN="LEFT"
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WIDTH="100%"><TABLE
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SUMMARY="Footer navigation table"
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WIDTH="100%"
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BORDER="0"
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CELLPADDING="0"
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CELLSPACING="0"
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><TR
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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><A
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HREF="security-password.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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><A
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HREF="index.html"
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ACCESSKEY="H"
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>Home</A
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></TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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><A
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HREF="security-dumb.html"
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ACCESSKEY="N"
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>Next</A
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></TD
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></TR
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><TR
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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>Use good passwords</TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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><A
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HREF="security.html"
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ACCESSKEY="U"
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>Up</A
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></TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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>Use or configure a dumb modem</TD
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></TR
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></TABLE
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></DIV
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></BODY
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></HTML
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> |