1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
|
<html>
<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>
|
