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+
+<head>
+<meta http-equiv="Content-Language" content="en-us">
+<meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
+<title>Content</title>
+<base target="_self">
+</head>
+
+<body background="../../images/bg.gif" topmargin="0" leftmargin="0" marginheight="0" marginwidth="0" onLoad="window.focus();" link="#808080" vlink="#808080" alink="#808080">
+
+<table border="0" cellpadding="0" cellspacing="0" width="100%">
+ <tr>
+ <td bgcolor="#336666" width="18" valign="top">
+ <img border="0" src="../../images/content_lines.gif" width="16" height="25">
+ <img border="0" src="../../images/transdot.gif" width="2" height="1"></td>
+ <td bgcolor="#336666"><b><font face="Arial" size="2" color="#FFFFFF">6.2</b></font></td>
+ <td bgcolor="#336666"><img border="0" src="../../images/transdot.gif" width="10" height="1"></td>
+ <td bgcolor="#336666" width="100%"><strong><font size="2" color="#FFFFFF">
+ <span style="font-family: Arial">Network Management</span></font></strong></td>
+ <td width="9" bgcolor="#336666"> </td>
+ </tr>
+ <tr>
+ <td bgcolor="#669999" height="25" width="18"> </td>
+ <td bgcolor="#669999" height="25"><b>
+ <font face="Arial" size="2" color="#FFFFFF">6.2.4</font></b></td>
+ <td bgcolor="#669999"><img border="0" src="../../images/transdot.gif" width="10" height="1"></td>
+ <td bgcolor="#669999" height="25" width="100%"><strong>
+ <font face="Arial" size="2" color="#FFFFFF">SNMP operation</font></strong></td>
+ <td bgcolor="#669999" height="25" width="9"> </td>
+ </tr></table>
+
+<table border="0" cellpadding="0" cellspacing="0" width="95%" bordercolor="#111111">
+ <tr>
+ <td width="15"></td>
+ <td>
+
+ <font face="Arial" size="2">Simple Network Management Protocol (SNMP)
+ is an application layer protocol designed to facilitate the exchange
+ of management information between network devices. By using SNMP to
+ access management information data, such as packets per second sent on
+ an interface or number of open TCP connections, network administrators can more easily manage
+ network performance to find and solve network problems.</font><p>
+
+ <font face="Arial" size="2">Today, SNMP is the most popular protocol
+ for managing diverse commercial, university, and research
+ internetworks.</font></p>
+ <p>
+
+ <font face="Arial" size="2">Standardization activity continues even as
+ vendors develop and release state-of-the-art SNMP-based management
+ applications. SNMP is a simple protocol, yet its feature set is
+ sufficiently powerful to handle the difficult problems involved with
+ the management of heterogeneous networks.</font></p>
+ <p>
+
+ <font face="Arial" size="2">The organizational model for SNMP based network management includes
+ four elements:</font></p>
+ <ul>
+ <li>
+
+ <font face="Arial" size="2">Management station </font></li>
+ <li>
+
+ <font face="Arial" size="2">Management agent</font></li>
+ <li>
+
+ <font face="Arial" size="2">Management information base</font></li>
+ <li>
+
+ <font face="Arial" size="2">Network management protocol</font></li>
+ </ul>
+ <p>
+
+ <font size="2" face="Arial">The network management station (NMS) is
+ usually a standalone workstation, but it may be implemented over
+ several systems. It
+ includes a collection of software called the network management
+ application (NMA). The NMA includes a user interface to allow
+ authorized network managers to manage the network. It responds to user
+ commands and issued commands to management agents throughout the
+ network. The management agents are key network platforms and devices,
+ other hosts, routers, bridges and hubs, equipped with SNMP so that
+ they can be managed. They respond to requests for information and
+ requests for actions from the NMS, such as polling, and may provide the NMS
+ with important but unsolicited information, such as traps. All the management
+ information of a particular agent is stored in the management
+ information base on that agent. An agent might keep track of the
+ following:</font></p>
+ <ul>
+ <li>
+
+ <font face="Arial" size="2">Number and state of its virtual circuits</font></li>
+ <li>
+
+ <font face="Arial" size="2">Number of certain kinds of error messages
+ received</font></li>
+ <li>
+
+ <font face="Arial" size="2">Number of bytes and packets in and out of
+ the device</font></li>
+ <li>
+
+ <font face="Arial" size="2">Maximum output queue length, for routers
+ and other internetworking devices</font></li>
+ <li>
+
+ <font face="Arial" size="2">Broadcast messages sent and received</font></li>
+ <li>
+
+ <font face="Arial" size="2">Network interfaces going down and coming
+ up</font></li>
+ </ul>
+ <p>
+
+ <font face="Arial" size="2">The NMS performs a monitoring function by
+ retrieving the values from the MIB. The NMS can cause an action to
+ take place at an agent. The
+ communication between the manager and the agent is carried out by an
+ application layer network management protocol. SNMP uses User Datagram
+ Protocol (UDP) and communicates over ports 161 and 162. It is based on
+ an exchange of messages. There are three common message types:</font></p>
+ <ul>
+ <li>
+
+ <font face="Arial" size="2"><b>Get</b> – Enables the management station to retrieve the value of MIB
+ objects from the agent.</font></li>
+ <li>
+
+ <font face="Arial" size="2"><b>Set</b> – Enables the management station to set the value of MIB
+ objects at the agent.</font></li>
+ <li>
+
+ <font face="Arial" size="2"><b>Trap</b> – Enables the agent to notify
+ the management station of significant events.</font></li>
+ </ul>
+ <p>
+
+ <font face="Arial" size="2">This model is referred to as a two-tier model.
+ <img border="0" src="../../images/1.gif" align="absmiddle" width="12" height="12"> However, it assumes
+ that all network elements are manageable by SNMP. This is not always
+ the case, as some devices have a proprietary management interface. In
+ these cases, a three-tiered model is required.
+ <img border="0" src="../../images/2.gif" align="absmiddle" width="12" height="12"> A network manager
+ who wants to obtain information or control this proprietary node
+ communicates with a proxy agent. The proxy agent then translates the
+ manager’s SNMP request into a form appropriate to the target system and
+ uses whatever proprietary management protocol is appropriate to
+ communicate with the target system. Responses from the target to
+ the proxy are translated into SNMP messages and
+ communicated back to the manager. </font>
+ </p>
+ <p>
+
+ <font face="Arial" size="2">Network management applications often
+ offload some network management functionality to a remote monitor (RMON)
+ probe. The RMON probe gathers management information locally, and then
+ the network manager periodically retrieves a summary of this data.</font></p>
+ <p>
+
+ <font face="Arial" size="2">The NMS is an ordinary workstation, running a typical operating
+ system. <img border="0" src="../../images/3.gif" align="absmiddle" width="12" height="12"> It
+ has a large amount of RAM, to hold all the management
+ applications running at the same time. The manager runs a typical network
+ protocol stack, such as TCP/IP. The network management applications
+ rely on the host operating system, and on the communication
+ architecture. Examples of network management applications are
+ Ciscoworks2000, HP Openview, and SNMPv2c.</font></p>
+ <p>
+
+ <font face="Arial" size="2">As discussed before, the manager may be a standalone, centralized
+ workstation sending out queries to all agents, no matter where they
+ are located.
+ <img border="0" src="../../images/4.gif" align="absmiddle" width="12" height="12"> In a distributed network, a decentralized architecture is
+ more appropriate, with local NMS at each site. These distributed NMS
+ can act in a client-server architecture, in which one NMS acts as a
+ master server, and the others are clients. The clients send their data
+ to the master server for centralized storage.
+ <img border="0" src="../../images/5.gif" align="absmiddle" width="12" height="12"> An alternative
+ is that all distributed NMSs have equal responsibility, each with
+ their own manager databases, so the management information is
+ distributed over the peer NMSs.
+ <img border="0" src="../../images/6.gif" align="absmiddle" width="12" height="12"></font></p>
+ <p>
+ <TABLE bgcolor="#B0AFAF" width="95%" border="0" cellspacing="0" cellpadding="0">
+ <TR>
+ <TD valign="top">
+ <TABLE bgcolor="#669999" width="100%" cellspacing="0" cellpadding="0" border="0">
+ <TR>
+ <TD width="5">
+ <img border="0" src="../../images/lab_toplft.gif" width="116" height="23"></TD>
+ <TD><IMG alt="" height="1" width="3" src="../../images/s.gif"></TD><TD align="right" valign="top">
+ <IMG alt="" src="../../images/corner_ur_7.gif" width="7" height="7"></TD>
+ </TR>
+ </TABLE>
+
+ <TABLE bgcolor="#B0AFAF" width="100%" cellspacing="0" cellpadding="0" border="0">
+ <TR>
+ <TD>
+ <TABLE width="100%" cellpadding="2" cellspacing="0" border="0" bordercolor="#111111">
+ <TR>
+ <TD bgcolor="#ffffff" width="15"> </TD>
+ <TD bgcolor="#ffffff"><font FACE="Arial" SIZE="2" COLOR="#000000">
+ <p><font color="#808080">
+ <img border="0" src="../../images/links_icon.gif" width="25" height="25">
+ <b>Web Links</b></font></p>
+ </font><font FACE="Arial" SIZE="2" COLOR="#808080">
+
+ <p>SNMP and MIB Basics<p>
+ <a target="_blank" href="http://www.adventnet.com/products/cagent/help/Preface/intro_snmpmib.html">
+ http://www.adventnet.com/products/
+ cagent/help/ Preface/ intro_snmpmib.html</a></font></p>
+
+ <p>
+ <IMG alt="" height="2" width="1" src="../../images/s.gif"></p>
+ </TD>
+ </TR>
+ </TABLE>
+ </TD>
+ </TR>
+ </TABLE>
+ </TD>
+ </TR>
+ </TABLE><p>
+
+ <font face="Arial" size="2"> </font>
+ </td>
+ </tr>
+ </table>
+
+</body>
+
+</html>
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