The International Organization for Standardization (ISO) network
management model defines five functional areas of network management. This
document covers all functional areas. The overall purpose of this document is
to provide practical recommendations on each functional area to increase the
overall effectiveness of current management tools and practices. It also
provides design guidelines for future implementation of network management
tools and technologies.
The ISO network management model's five functional areas are listed
Fault Management—Detect, isolate, notify, and correct faults
encountered in the network.
Configuration Management—Configuration aspects of network devices
such as configuration file management, inventory management, and software
Performance Management—Monitor and measure various aspects of
performance so that overall performance can be maintained at an acceptable
Security Management—Provide access to network devices and corporate
resources to authorized individuals.
Accounting Management—Usage information of network resources.
The following diagram shows a reference architecture that Cisco Systems
believes should be the minimal solution for managing a data network. This
architecture includes a Cisco CallManager server for those who plan to manage
Voice over Internet Protocol (VoIP): The diagram shows how you would integrate
the CallManager server into the NMS topology.
The network management architecture includes the following:
Simple Network Management Protocol (SNMP) platform for fault
Performance monitoring platform for long term performance management
CiscoWorks2000 server for configuration management, syslog
collection, and hardware and software inventory management
Some SNMP platforms can directly share data with the CiscoWorks2000
server using Common Information Model/eXtensible Markup Language (CIM/XML)
methods. CIM is a common data model of an implementation-neutral schema for
describing overall management information in a network/enterprise environment.
CIM is comprised of a specification and a schema. The specification defines the
details for integration with other management models such as SNMP MIBs or
Desktop Management Task Force Management Information Files (DMTF MIFs), while
the schema provides the actual model descriptions.
XML is a markup language used for representing structured data in
textual form. A specific goal of XML was to keep most of the descriptive power
of SGML whilst removing as much of the complexity as possible. XML is similar
in concept to HTML, but whereas HTML is used to convey graphical information
about a document, XML is used to represent structured data in a document.
Cisco's advanced services customers would also include Cisco's NATkit
server for additional proactive monitoring and troubleshooting. The NATkit
server would either have a remote disk mount (rmount) or file transfer protocol
(FTP) access to the data residing on the CiscoWorks2000 server.
Management Basics chapter of the Internetworking Technology
Overview provides a more detailed overview regarding network
The goal of fault management is to detect, log, notify users of, and
(to the extent possible) automatically fix network problems to keep the network
running effectively. Because faults can cause downtime or unacceptable network
degradation, fault management is perhaps the most widely implemented of the ISO
network management elements.
A network management platform deployed in the enterprise manages an
infrastructure that consists of multivendor network elements. The platform
receives and processes events from network elements in the network. Events from
servers and other critical resources can also be forwarded to a management
platform. The following commonly available functions are included in a standard
Topology mapping of network elements
Performance data collector and grapher
Management data browser
Network management platforms can be viewed as the main console for
network operations in detecting faults in the infrastructure. The ability to
detect problems quickly in any network is critical. Network operations
personnel can rely on a graphical network map to display the operational states
of critical network elements such as routers and switches.
Network management platforms such HP OpenView, Computer Associates
Unicenter, and SUN Solstice can perform a discovery of network devices. Each
network device is represented by a graphical element on the management
platform's console. Different colors on the graphical elements represent the
current operational status of network devices. Network devices can be
configured to send notifications, called SNMP traps, to network management
platforms. Upon receiving the notifications, the graphical element representing
the network device changes to a different color depending on the severity of
the notification received. The notification, usually called an event, is placed
in a log file. It is particularly important that the most current Cisco
Management Information Base (MIB) files be loaded on the SNMP platform to
ensure that the various alerts from Cisco devices are interpreted correctly.
Cisco publishes the MIB files for managing various network devices. The
files are located on the cisco.com website, and include the following
MIB files published in SNMPv1 format
MIB files published in SNMPv2 format
Supported SNMP traps on Cisco devices
OIDs for Cisco current SNMP MIB
A number of network management platforms are capable of managing
multiple geographically distributed sites. This is accomplished by exchanging
management data between management consoles at remote sites with a management
station at the main site. The main advantage of a distributed architecture is
that it reduces management traffic, thus, providing a more effective usage of
bandwidth. A distributed architecture also allows personnel to locally manage
their networks from remote sites with systems.
A recent enhancement to management platforms is the ability to remotely
management network elements using a web interface. This enhancement eliminates
the need for special client software on individual user stations to access a
A typical enterprise is comprised of different network elements.
However, each device normally requires vendor-specific element management
systems in order to effectively manage the network elements. Therefore,
duplicate management stations may be polling network elements for the same
information. The data collected by different systems is stored in separate
databases, creating administration overhead for users. This limitation has
prompted networking and software vendors to adopt standards such as Common
Object Request Broker Architecture (CORBA) and Computer-Integrated
Manufacturing (CIM) to facilitate the exchange of management data between
management platforms and element management systems. With vendors adopting
standards in management system development, users can expect interoperability
and cost savings in deploying and managing the infrastructure.
CORBA specifies a system that provides interoperability between objects
in a heterogeneous, distributed environment and in a manner that is transparent
to the programmer. Its design is based on the Object Management Group (OMG)
Trivial File Transfer Protocol (TFTP) and system log (syslog) servers
are crucial components of a troubleshooting infrastructure in network
operations. The TFTP server is used primarily for storing configuration files
and software images for network devices. Routers and switches are capable of
sending system log messages to a syslog server. The messages facilitate the
troubleshooting function when problems are encountered. Occasionally, Cisco
support personnel need the syslog messages to perform root cause analysis.
The CiscoWorks2000 Resource Management Essentials (Essentials)
distributed syslog collection function allows for the deployment of several
UNIX or NT collection stations at remote sites to perform message collection
and filtering. The filters can specify which syslog messages will be forwarded
to the main Essentials server. A major benefit of implementing distributed
collection is the reduction of messages forwarded to the main syslog servers.
The purpose of fault management is to detect, isolate, notify, and
correct faults encountered in the network. Network devices are capable of
alerting management stations when a fault occurs on the systems. An effective
fault management system consists of several subsystems. Fault detection is
accomplished when the devices send SNMP trap messages, SNMP polling, remote
monitoring (RMON) thresholds, and syslog messages. A management system alerts
the end user when a fault is reported and corrective actions can be
Traps should be enabled consistently on network devices. Additional
traps are supported with new Cisco IOS software releases for routers and
switches. It is important to check and update the configuration file to ensure
the proper decoding of traps. A periodic review of configured traps with the
Cisco Assured Network Services (ANS) team will ensure effective fault detection
in the network.
The following table lists the CISCO-STACK-MIB traps that are supported
by, and can be used to monitor fault conditions on, Cisco Catalyst local area
network (LAN) switches.
The agent entity has detected that the
moduleStatus object in this MIB has transitioned to the
ok(2) state for one of its modules.
The agent entity has detected that the
moduleStatus object in this MIB has transitioned out of
the ok(2) state for one of its modules.
The agent entity has detected that the
or chassisMajorAlarm object in this MIB has transitioned
to the on(2) state.
A chassisMajorAlarm indicates that one of
the following conditions exists:
Any voltage failure
Simultaneous temperature and fan failure
One hundred percent power supply failure (two out of two, or
one out of one)
A chassisMinorAlarm indicates that one of the following
Partial power supply failure (one out of two)
Two power supplies of incompatible type
The agent entity has detected that the
or chassisMajorAlarm object in this MIB has transitioned
to the off(1) state.
Environmental monitor (envmon) traps are defined in CISCO-ENVMON-MIB
trap. The envmon trap sends Cisco enterprise-specific environmental monitor
notifications when an environmental threshold is exceeded. When envmon is used,
a specific environmental trap type can be enabled, or all trap types from the
environmental monitor system can be accepted. If no option is specified, all
environmental types are enabled. It can be one or more of the following
voltage—A ciscoEnvMonVoltageNotification is sent if the voltage
measured at a given test point is outside the normal range for the test point
(such as is at the warning, critical, or shutdown stage).
shutdown—A ciscoEnvMonShutdownNotification is sent if the
environmental monitor detects that a test point is reaching a critical state
and is about to initiate a shutdown.
supply—A ciscoEnvMonRedundantSupplyNotification is sent if the
redundant power supply (where extant) fails.
fan—A ciscoEnvMonFanNotification is sent if any one of the fans in
the fan array (where extant) fails.
temperature—A ciscoEnvMonTemperatureNotification is sent if the
temperature measured at a given test point is outside the normal range for the
test point (such as is at the warning, critical, or shutdown stage).
Fault detection and monitoring of network elements can be expanded from
the device level to the protocol and interface levels. For a network
environment, fault monitoring can include Virtual Local Area Network (VLAN),
asynchronous transfer mode (ATM), fault indications on physical interfaces, and
so forth. Protocol-level fault management implementation is available using an
element management system such as the CiscoWorks2000 Campus Manager. The
TrafficDirector application in Campus Manager focuses on switch management
utilizing mini-RMON support on Catalyst switches.
With an increasing number of network elements and complexity of network
issues, an event management system that is capable of correlating different
network events (syslog, trap, log files) may be considered. This architecture
behind an event management system is comparable to a Manager of Managers (MOM)
system. A well-designed event management system allows personnel in the network
operations center (NOC) to be proactive and effective in detecting and
diagnosing network issues. Event prioritization and suppression allow network
operation personnel to focus on critical network events, investigate several
event management systems including the Cisco Info Center, and conduct a
feasibility analysis to fully explore the capabilities of such systems. To
obtain more information, go to the
RMON alarm and event are two groups defined in the RMON specification.
Normally, a management station performs polling on network devices to determine
the status or value of certain variables. For example, a management station
polls a router to find out the central processing unit (CPU) utilization and
generate an event when the value hits reaches a configured threshold. This
method wastes network bandwidth and can also miss the actual threshold
depending on the polling interval.
With RMON alarm and events, a network device is configured to monitor
itself for rising and falling thresholds. At a predefined time interval, the
network device will takes a sample of a variable and compares it against the
thresholds. An SNMP trap can be sent to a management station if the actual
value exceeds or falls below the configured thresholds. RMON alarm and event
groups provide a proactive method of managing critical network devices.
Cisco Systems recommends implementing RMON alarm and event on critical
network devices. Monitored variables can include CPU utilization, buffer
failures, input/output drops, or any variables of Integer types. Starting with
Cisco IOS Software Release 11.1(1), all router images support RMON alarm and
RMON memory usage is constant across all switch platforms relating to
statistics, histories, alarms, and events. RMON uses what is called a
bucket to store histories and statistics on the RMON agent
(which is the switch in this case). The bucket size is defined on the RMON
probe (SwitchProbe device) or RMON application (TrafficDirector tool), then
sent to the switch to be set.
Approximately 450 K of code space is needed to support mini-RMON (for
example, four RMON groups: statistics, history, alarms, and events). The
dynamic memory requirement for RMON varies because it depends on the runtime
The following table defines the runtime RMON memory usage information
for each mini-RMON group.
RMON Group Definition
DRAM Space Used
140 bytes per switched Ethernet/Fast Ethernet
3.6 K for 50 buckets *
Each additional bucket uses 56 bytes
Alarm and Event
2.6 K per alarm and its corresponding event
Per alarm per port
*RMON uses what is called a bucket to store
histories and statistics on the RMON agent (such as a switch).
By incorporating RMON as part of a fault management solution, a user
can proactively monitor the network before a potential problem occurs. For
example, if the number of broadcast packets received increases significantly,
it can cause an increase in CPU utilization. By implementing RMON alarm and
event, a user can set up a threshold to monitor the number of broadcast packets
received and alert the SNMP platform by means of an SNMP trap if the configured
threshold is reached. RMON alarms and events eliminate the excessive polling
normally performed by the SNMP platform for accomplishing the same goal.
Two methods are available from which to configure RMON alarm and event:
Command-line interface (CLI)
The following sample procedures show how to set a threshold to monitor
the number of broadcast packets received on an interface. The same counter is
used in these procedures as is shown in the show interface command
example at the end of this section.
Command-line Interface Example
To implement RMON alarm and event using the CLI interface, perform the
Find the interface index associated with Ethernet 0 by walking the
Obtain the OID associated with the CLI field to be monitored. For
this example, the OID for 'broadcasts' is 126.96.36.199.188.8.131.52.1.12. The
Cisco OIDs for specific
MIB variables are available from the cisco.com
Determine the following parameters for setting up thresholds and
rising and falling thresholds
sampling type (absolute or delta)
action when threshold is reached
For the purpose of this example, a threshold is being set up to
monitor the number of broadcast packets received on Ethernet 0. A trap will be
generated if the number of broadcast packets received is greater than 500
between 60-second samples. The threshold will be reactivated when the number of
input broadcasts does not increase between samples taken.
Note: For detailed about these command parameters, check the Cisco
Connection Online (CCO) documentation for RMON alarm and event commands for
your particular Cisco IOS version.
Specify the trap sent (RMON event) when the threshold is reached
using the following CLI commands (The Cisco IOS commands are displayed in
The goal of configuration management is to monitor network and system
configuration information so that the effects on network operation of various
versions of hardware and software elements can be tracked and managed.
With an increasing number of network devices deployed, it is critical
to be able to accurately identify the location of a network device. This
location information should provide a detailed description meaningful to those
tasked with dispatching resources when a network problem occurs. To expedite a
resolution if a network problem occurs, make certain to have available contact
information of the person or department responsible for the devices. Contact
information should include telephone number and the name of the person or
Naming conventions for network devices, starting from device name to
individual interface, should be planned and implemented as part of the
configuration standard. A well defined naming convention provides personnel
with the ability to provide accurate information when troubleshooting network
problems. The naming convention for devices can use geographical location,
building name, floor, and so forth. For the interface naming convention, it can
include the segment to which a port is connected, name of connecting hub, and
so forth. On serial interfaces, it should include actual bandwidth, local data
link connection identifier (DLCI) number (if Frame Relay), destination, and the
circuit ID or information provided by the carrier.
When you add new configuration commands on existing network devices
needs, you must verify the commands for integrity before actual implementation
takes place. An improperly configured network device can have a disastrous
effect on network connectivity and performance. Configuration command
parameters must be checked to avoid mismatches or incompatibility issues. It is
advisable to schedule a thorough review of configurations with Cisco engineers
on a regular basis.
A fully functional CiscoWorks2000 Essentials allows for backing up
configuration files on routers and Cisco Catalyst switches automatically. The
security feature of Essentials can be used to perform authentication on
configuration changes. A change audit log is available to track changes and the
user name of individuals issuing changes. For configuration changes on multiple
devices, two options are available: the web-based NetConfig in the current
version of CiscoWorks2000 Essentials or the cwconfig
script. Configuration files can be downloaded and uploaded using CiscoWorks2000
Essentials utilizing the predefined or user-defined templates.
These functions can be accomplished with the configuration management
tools in CiscoWorks2000 Essentials:
Push configuration files from the Essentials configuration archive to
a device or multiple devices
Pull the configuration from the device to the Essentials archive
Extract the latest configuration from the archive and write it to a
Import configuration from a file and push the configuration to
Compare the last two configurations in the Essentials archive
Delete configurations older than a specified date or version from the
Copy the startup configuration to the running configuration
The discovery function of most network management platforms is intended
to provide a dynamic listing of devices found in the network. Discovery engines
such as those implemented in network management platforms should be utilized.
An inventory database provides detailed configuration information on
network devices. Common information includes models of hardware, installed
modules, software images, microcode levels, and so on. All these pieces of
information are crucial in completing tasks such as software and hardware
maintenance. The up-to-date listing of network devices collected by the
discovery process can be used as a master list to collect inventory information
using SNMP or scripting. A device list may be imported from CiscoWorks2000
Campus Manager into the inventory database of CiscoWorks2000 Essentials to
obtain an up-to-date inventory of Cisco Catalyst switches.
A successful upgrade of Cisco IOS images on network devices requires a
detailed analysis of the requirements such as memory, boot ROM, microcode
level, and so on. The requirements are normally documented and available on
Cisco's web site in the form of release notes and installation guides. The
process of upgrading a network device running Cisco IOS includes downloading a
correct image from CCO, backing up the current image, making sure all hardware
requirements are met, and then loading the new image into the device.
The upgrade window to complete device maintenance is fairly limited for
some organizations. In a large network environment with limited resources, it
might be necessary to schedule and automate software upgrades after business
hours. The procedure can be completed either using scripting language such as
Expect or an application written specifically to perform such a task.
Changes to software in network devices such as Cisco IOS images and
microcode versions should be tracked to assist in the analysis phase when
another software maintenance is required. With a modification history report
readily available, the person performing the upgrade can minimize the risk of
loading incompatible images or microcode into network devices.
A service level agreement (SLA) is a written agreement between a
service provider and their customers on the expected performance level of
network services. The SLA consists of metrics agreed upon between the provider
and its customers. The values set for the metrics must be realistic,
meaningful, and measurable for both parties.
Various interface statistics can be collected from network devices to
measure the performance level. These statistics can be included as metrics in
the SLA. Statistics such as input queue drops, output queue drops, and ignored
packets are useful for diagnosing performance-related problems.
At the device level, performance metrics can include CPU utilization,
buffer allocation (big buffer, medium buffer, misses, hit ratio), and memory
allocation. The performance of certain network protocols is directly related to
buffer availability in network devices. Measuring device-level performance
statistics are critical in optimizing the performance of higher-level
Network devices such as routers support various higher-layer protocols
such as Data Link Switching Workgroup (DLSW), Remote Source Route Bridging
(RSRB), AppleTalk, and so forth. Performance statistics of wide-area network
(WAN) technologies including Frame Relay, ATM, Integrated Services Digital
Network (ISDN), and others can be monitored and collected.
Different performance metrics at the interface, device, and protocol
levels should be collected on a regular basis using SNMP. The polling engine in
a network management system can be utilized for data collection purposes. Most
network management systems are capable of collecting, storing, and presenting
Various solutions are available in the marketplace to address the needs
of performance management for enterprise environments. These systems are
capable of collecting, storing, and presenting data from network devices and
servers. The web-based interface on most products makes the performance data
accessible from anywhere in the enterprise. Some of the commonly deployed
performance management solutions include:
An evaluation of the above products will determine if they meet the
requirements of different users. Some vendors support integration with network
management and system management platforms. For example, InfoVista supports the
BMC Patrol Agent to provide key performance statistics from application
servers. Each product has a different pricing model and capabilities with the
base offering. Support for performance management features for Cisco's devices
such as NetFlow, RMON, and Cisco IOS Service Assurance Agent/Response Time
Reporter (RTR/SAA CSAA/RTR) is available on some solutions. Concord has
recently added support for Cisco's WAN switches that can be used to collect and
view performance data.
The CSAA/RTR Service Assurance Agent (SAA)/Response Time Reporter (RTR)
feature in Cisco IOS can be utilized for measuring the response time between IP
devices. A source router configured with CSAA configured is capable of
measuring the response time to a destination IP device that can be a router or
an IP device. The response time can be measured between the source and the
destination or for each hop along the path. SNMP traps can be configured to
alert management consoles if the response time exceeds the predefined
Recent enhancements to Cisco IOS extends the capabilities of CSAA to
measure the following:
HyperText Transfer Protocol (HTTP) service performance
Domain name system (DNS) lookup
Transmission control protocol (TCP) connect
HTTP transaction time
Interpacket delay variance (jitter) of Voice over IP (VoIP) traffic
Response time between end points for a specific quality of service
IP type of service (ToS) bits
Packet loss using CSAA generated packets
Configuring the CSAA feature on routers can be accomplished using the
Cisco Internetwork Performance Monitor (IPM) application. The CSAA/RTR is
imbedded in many but not all feature sets of the Cisco IOS software. A release
of the Cisco IOS software release that supports CSAA/RTR must be installed on
the device that IPM uses to collect performance statistics. For a summary of
Cisco IOS versions that support CSAA/RTR/IPM, refer to the
Frequently Asked Questions website.
User traffic has increased significantly and has placed a higher demand
on network resources. Network managers typically have a limited view on the
types of traffic running in the network. User and application traffic profiling
provides a detailed view of the traffic in the network. Two technologies, RMON
probes and NetFlow, provide the ability to collect traffic profiles.
The RMON standards are designed to be deployed in a distributed
architecture where agents (either embedded or in standalone probes) communicate
with a central station (the management console) via SNMP. The RFC 1757 RMON
standard organizes monitoring functions into nine groups to support Ethernet
topologies, and adds a tenth group in RFC 1513 for Token Ring-unique
parameters. Fast Ethernet link monitoring is provided in the framework of the
RFC 1757 standard, and Fiber-Distributed Data Interface (FDDI) ring monitoring
is provided in the framework of both RFC 1757 and RFC 1513.
The emerging RFC 2021 RMON specification drives remote monitoring
standards beyond the Media Access Control (MAC) layer to the network and
application layers. This setup enables administrators to analyze and
troubleshoot networked applications such as Web traffic, NetWare, Notes,
e-mail, database access, Network File System (NFS), and others. RMON alarms,
statistics, history, and host/conversation groups can now be used to
proactively monitor and maintain network availability based on
application-layer traffic-the most critical traffic in the network. RMON2
enables network administrators to continue their deployment of standards-based
monitoring solutions to support mission-critical, server-based applications.
The following tables list the functions of the RMON groups.
RMON Group (RFC 1757)
Counters for packets, octets, broadcasts, errors, and offers on
the segment or port.
Periodically samples and saves statistics group counters for
Maintains statistics on each host device on the segment or
Host Top N
A user-defined subset report of the Hosts group, sorted by a
statistical counter. By returning only the results, management traffic is
Maintains conversation statistics between hosts on the
A threshold that can be set on critical RMON variables for
Generates SNMP traps and log entries when an Alarms group
threshold is exceeded.
Manages buffers for packets captured by the Filter group for
uploading to the management console.
Ring station—detailed statistics on individual stations
Ring station order—an ordered list of stations currently on the
Ring station configuration—configuration and insertion/removal
Source routing—statistics on source routing, such as hop counts,
Protocols for which the agent monitors and maintains
Statistics for each protocol.
Network Layer Host
Statistics for each network layer address on the segment, ring,
Network Layer Matrix
Traffic statistics for pairs of network layer
Application Layer Host
Statistics by application layer protocol for each network
Application Layer Matrix
Traffic statistics by application layer protocol for pairs of
network layer addresses.
Extends history beyond RMON1 link-layer statistics to include any
RMON, RMON2, MIB-I, or MIB-II statistics.
MAC-to-network layer address bindings.
Agent capabilities and configurations.
The Cisco NetFlow feature allows detailed statistics of traffic flows
to be collected for capacity planning, billing, and troubleshooting functions.
NetFlow can be configured on individual interfaces, providing information on
traffic passing through those interfaces. The following types of information
are part of the detailed traffic statistics:
Source and destination IP addresses
Input and output interface numbers
TCP/UDP source port and destination ports
Number of bytes and packets in the flow
Source and destination autonomous system numbers
IP type of service (ToS)
NetFlow data gathered on network devices is exported to a collector
machine. The collector performs functions such as reducing the volume of data
(filtering and aggregation), hierarchical data storage, and file system
management. Cisco provides NetFlow Collector and NetFlow Analyzer applications
for gathering and analyzing data from routers and Cisco Catalyst switches.
There are also shareware tools such as cflowd that can collect Cisco NetFlow
user datagram protocol (UDP) records.
NetFlow data is transported using UDP packets in three different
Version 1—The original format supported in the initial NetFlow
Version 5—A later enhancement that added Border Gateway Protocol
(BGP) autonomous system information and flow sequence numbers.
Version 7—A still later enhancement that added NetFlow switching
support for Cisco Catalyst 5000 series switches equipped with a NetFlow feature
Versions 2 through 4 and Version 6 were either not released or are not
supported by FlowCollector. In all three versions, the datagram consists of a
header and one or more flow records.
Cisco Catalyst 5000 with NetFlow Feature Card
* Support for NetFlow Export V1, V5, and V8 on Cisco 1600 and 2500
platforms is targeted for Cisco IOS Software Release 12.0(T). NetFlow support
for these platforms is not available in the Cisco IOS 12.0 mainline release.
** Support for NetFlow V1, V5, and V8 on the AS5300 platform is
targeted for Cisco IOS Software Release 12.06(T).
*** MLS and NetFlow data export is supported in Catalyst 5000 series
supervisor engine software release 4.1(1) or later.
The goal of security management is to control access to network
resources according to local guidelines so that the network cannot be sabotaged
(intentionally or unintentionally). A security management subsystem, for
example, can monitor users logging on to a network resource, refusing access to
those who enter inappropriate access codes. Security management is a very broad
subject; therefore this area of the document only covers security as related to
SNMP and basic device access security.
Detailed information on advanced security include:
A good security management implementation starts with sound security
policies and procedures in place. It is important to create a platform-specific
minimum configuration standard for all routers and switches that follow
industry best practices for security and performance.
There are various methods of controlling access on Cisco routers and
catalyst switches. Some of these methods include:
Access Control Lists (ACL)
User IDs and passwords local to the device
Terminal Access Controller Access Control System (TACACS)
TACACS is an Internet Engineering Task Force (RFC 1492) standard
security protocol that runs between client devices on a network and against a
TACACS server. TACACS is an authentication mechanism that is used to
authenticate the identity of a device seeking remote access to a privileged
database. Variations of TACACS include TACACS+, the AAA architecture that
separates authentication, authorization, and accounting functions.
TACACS+ is used by Cisco to allow a finer control over who can access
the Cisco device in non-privileged and privileged mode. Multiple TACACS+
servers can be configured for fault tolerance. With TACACS+ enabled, the router
and switch prompts the user for a user name and password. Authentication can be
configured for login control or to authenticate individual commands.
Authentication is the process of identifying users, including login and
password dialog, challenge and response, and messaging support. Authentication
is the way a user is identified prior to being allowed access to the router or
switch. There is a fundamental relationship between authentication and
authorization. The more authorization privileges a user receives, the stronger
the authentication should be.
Authorization provides remote access control, including one-time
authorization and authorization for each service that is requested by the user.
On a Cisco router, the authorization level range for users is 0 to 15 with 0
being the lowest level and 15 the highest.
Accounting allows for the collecting and sending of security
information used for billing, auditing, and reporting, such as user identities,
start and stop times, and executed commands. Accounting enables network
managers to track the services that users are accessing as well as the amount
of network resources they are consuming.
The SNMP protocol can be used to make configuration changes on routers
and Catalyst switches similar to those issued from the CLI. Proper security
measures should be configured on network devices to prevent unauthorized access
and change via SNMP. Community strings should follow the standard password
guidelines for length, characters, and difficulty of guessing. It is important
to change the community strings from their public and private defaults.
All SNMP management host(s) should have a static IP address and be
explicitly granted SNMP communication rights with the network device by that
predefined by IP address and Access Control List (ACL). Cisco IOS and Cisco
Catalyst software provides security features that ensure that only authorized
management stations are allowed to perform changes on network devices.
Router Security Features
SNMP Privilege Level
This feature limits the types of operations that a management station
can have on a router. There are two types of privilege level on routers:
Read-Only (RO) and Read-Write (RW). The RO level only allows a management
station to query the router data. It does not allow for configuration commands
such as rebooting a router and shutting down interfaces to be performed. Only
the RW privilege level can be used to perform such operations.
SNMP Access Control List (ACL)
The SNMP ACL feature can be used in conjunction with the SNMP privilege
feature to limit specific management stations from requesting management
information from routers.
This feature limits specific information that can be retrieved from
routers by management stations. It can be used with the SNMP privilege level
and ACL features to enforce restricted access of data by management consoles.
For configuration samples of SNMP View, go to
SNMP Version 3
SNMP version 3 (SNMPv3) provides secure exchanges of management data
between network devices and management stations. The encryption and
authentication features in SNMPv3 ensure high security in transporting packets
to a management console. SNMPv3 is supported in Cisco IOS Software Release
12.0(3)T and later. For a technical overview of SNMPv3, go to
Access Control List (ACL) on Interfaces
The ACL feature provides security measures in preventing attacks such
as IP spoofing. The ACL can be applied on incoming or outgoing interfaces on
Catalyst LAN Switch Security Feature
IP Permit List
The IP Permit List feature restricts inbound Telnet and SNMP access to
the switch from unauthorized source IP addresses. Syslog messages and SNMP
traps are supported to notify a management system when a violation or
unauthorized access occurs.
A combination of the Cisco IOS security features can be used to manage
routers and Catalyst switches. A security policy needs to be established that
limits the number of management stations capable of accessing the switches and
Accounting management is the process used to measure network
utilization parameters so that individual or group users on the network can be
regulated appropriately for the purposes of accounting or chargeback. Similar
to performance management, the first step toward appropriate accounting
management is to measure the utilization of all important network resources.
Network resource utilization can be measured using the Cisco NetFlow and Cisco
IP Accounting features. Analysis of the data gathered through these methods
provides insight into current usage patterns.
A usage-based accounting and billing system is an essential part of any
service level agreement (SLA). It provides both a practical way of defining
obligations under an SLA and clear consequences for behavior outside the terms
of the SLA.
The data can be collected via probes or Cisco NetFlow. Cisco provides
NetFlow Collector and NetFlow Analyzer applications for gathering and analyzing
data from routers and Catalyst switches. Shareware applications such as cflowd
are also used to gather NetFlow data. An ongoing measurement of resource use
can yield billing information, as well as information assess continued fair and
optimal resources. Some commonly deployed accounting management solutions
NetFlow (network flow) is an input side-measurement technology that
allows for capturing the data required for network planning, monitoring, and
accounting applications. NetFlow should be deployed on edge/aggregation router
interfaces for service providers or WAN access router interfaces for Enterprise
Cisco Systems recommends a carefully planned NetFlow deployment with
NetFlow services activated on these strategically located routers. NetFlow can
be deployed incrementally (interface by interface) and strategically (on well
chosen routers), rather than deploying NetFlow on every router on the network.
Cisco personnel will work with customers to determine on which key routers and
key interfaces NetFlow should be activated based on the customer's traffic flow
patterns, network topology, and architecture.
Key deployment considerations include:
NetFlow services should be utilized as an edge metering and access
list performance acceleration tool and should not be activated on hot
core/backbone routers or routers running at very high CPU
Understand application-driven data collection requirements.
Accounting applications may only require originating and terminating router
flow information whereas monitoring applications may require a more
comprehensive (data intensive) end-to-end view.
Understand the impact of network topology and routing policy on flow
collection strategy. For example, avoid collecting duplicate flows by
activating NetFlow on key aggregation routers where traffic originates or
terminates and not on backbone routers or intermediate routers which would
provide duplicate views of the same flow information.
Service providers in the transit carrier
business (carrying traffic neither originating nor terminating on their
network) may utilize NetFlow Export data for measuring transit traffic usage of
network resources for accounting and billing purposes.
Cisco IP accounting support provides basic IP accounting functions. By
enabling IP accounting, users can see the number of bytes and packets switched
through the Cisco IOS software on a source and destination IP address basis.
Only transit IP traffic is measured and only on an outbound basis. Traffic
generated by the software or terminating in the software is not included in the
accounting statistics. To maintain accurate accounting totals, the software
maintains two accounting databases: an active and a check-pointed database.
Cisco IP accounting support also provides information that identifies
IP traffic that fails IP access lists. Identifying IP source addresses that
violate IP access lists signals possible attempts to breach security. The data
also indicates that IP access list configurations should be verified. To make
this feature available to users, enable IP accounting of access list violations
using the ip accounting access-violations command.
Users can then display the number of bytes and packets from a single source
that attempted to breach security against the access list for the source
destination pair. By default, IP accounting displays the number of packets that
have passed access lists and were routed.
To enable IP accounting, use one of the following commands for each
interface in interface configuration mode:
Enable basic IP accounting.
ip accounting access
Enable IP accounting with the ability to identify IP traffic that
fails IP access lists.
To configure other IP accounting functions, use one or more of the
following commands in global configuration mode:
Set the maximum number of accounting entries to be
ip accounting-list ip-address
Filter accounting information for hosts.
Control the number of transit records that will be stored in the
IP accounting database.