Performing Basic System Management
This module describes the basic tasks that you can perform to manage the general system features of the Cisco IOS software--those features that are generally not specific to a particular protocol.
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Information About Performing Basic System Management
- System Name
- Command Aliases
- Minor Services
- Hidden Telnet Addresses
- EXEC Startup Delay
- Idle Telnet Connections
- Interval for Load Data
- Number of TCP Transactions
- Switching and Scheduling Priorities
- System Buffer Size
System Name
The system name, also called the hostname, is used to uniquely identify the system in your network. The system name is displayed at the CLI prompt. If no name is configured, the system default name is Router.
Command Aliases
Command aliases allow you to configure alternative syntax for commands. You may want to create aliases for commonly used or complex commands. For example, you could assign the alias save config to the copy running-config startup-config command to reduce the amount of typing you have to perform, or if your users might find the save config command easier to remember. Use word substitutions or abbreviations to tailor the command syntax for you and your user community.
Remember that any aliases you configure will be effective only on your system, and that the original command syntax will appear in the configuration file.
Minor Services
Minor services are small servers that run on your routing device and are useful for basic system testing and for providing basic network functions. Minor services are useful for testing connections from another host on the network.
Cisco small servers are conceptually equivalent to daemons.
Small servers provided by Cisco IOS software-based devices include TCP, UDP, HTTP, Bootstrap Protocol (BOOTP), and Finger. For information about the HTTP server, see the “Using the Cisco Web Browser User Interface” chapter in the Cisco IOS Configuration Fundamentals Configuration Guide.
The TCP small server provides the following minor services:
- Chargen--Generates a stream of ASCII data. To test this service, issue the telnet a.b.c.d chargencommand from a remote host.
- Daytime--Returns the system date and time if you have configured Network Time Protocol (NTP) or set the date and time manually. To test this service, issue the telnet a.b.c.d daytimecommand from a remote host.
- Discard--Discards whatever you type. To test this service, issue the telnet a.b.c.d discardcommand from a remote host.
- Echo--Echoes back whatever you type. To test this service, issue the telnet a.b.c.d echocommand from a remote host.
The UDP small server provides the following minor services:
- Chargen--Discards the datagram that you send and responds with a 72-character string of ASCII characters terminated with a CR+LF (carriage return and line feed).
- Discard--Discards the datagram you send.
- Echo--Echoes the payload of the datagram that you send.
Minor services are disabled by default.
Caution |
Enabling minor services creates the potential for certain types of denial-of-service (DoS) attacks, such as the UDP diagnostic port attack. Therefore, any network device that has UDP, TCP, BOOTP, or Finger services should be protected by a firewall or have the minor services disabled. For information on preventing UDP diagnostic port attacks, see the white paper titled Defining Strategies to Protect Against UDP Diagnostic Port Denial of Service Attacks a vailable on Cisco.com. |
BOOTP Server
You can enable or disable an async line Bootstrap Protocol (BOOTP) service on your routing device. This small server is enabled by default. Due to security considerations, this service should be disabled if you are not using it.
Because DHCP is based on the BOOTP, both of these service share the well-known UDP server port 67 (per the Internet standards and RFCs). For more information about DHCP configuration in the Cisco IOS software, see the Cisco IOS IP Addressing Configuration Guide. For more information about BOOTP, see RFC 951. Interoperation between BOOTP and DHCP is defined in RFC 1534. DHCP is defined in RFC 2131.
Finger Protocol
The Finger protocol allows users throughout the network to get a list of the users currently using a particular routing device. The information displayed includes the processes running on the system, the line number, connection name, idle time, and terminal location. This information is provided through the Cisco IOS software show users EXEC command.
Hidden Telnet Addresses
You can hide addresses while attempting to establish a Telnet session. The hide feature suppresses the display of the address and continues to display all other messages that normally would be displayed during a connection attempt, such as detailed error messages if the connection fails.
EXEC Startup Delay
To delay the startup of the EXEC process on noisy lines until the line has been idle for 3 seconds, use the service exec-wait command in global configuration mode.
This command is useful on noisy modem lines or when a modem attached to the line is configured to ignore Microcom Networking Protocol (MNP) or V.42 negotiations, and when MNP or V.42 modems are dialing in. In these cases, noise or MNP/V.42 packets might be interpreted as usernames and passwords, causing authentication failure before the user can type a username or password. This command is not useful on nonmodem lines or lines without some kind of login configured.
Idle Telnet Connections
Normally, data sent to noncurrent Telnet connections is accepted and discarded. When the service telnet-zero-idle command is enabled and a session is suspended (that is, some other connection is made active), the TCP window is set to zero. This action prevents the remote host from sending any more data until the connection is resumed. Use this command when all messages sent by the host must be seen by the users and the users are likely to use multiple sessions. Do not use this command if your host will eventually time out and log out a TCP user whose window is zero.
Interval for Load Data
You can change the period of time over which a set of data is used for computing load statistics. Decisions, such as dial backup, depend on these statistics. If you decrease the load interval, the average statistics are computed over a shorter period of time and are more responsive to bursts of traffic.
Number of TCP Transactions
When you are using a standard TCP implementation to send keystrokes between machines, TCP tends to send one packet for each keystroke typed, which can use up the bandwidth and contribute to the congestion on larger networks.
John Nagle’s algorithm (RFC 896) helps alleviate the small-packet problem in TCP. The first character typed after the connection establishment is sent in a single packet, but TCP holds any additional characters that are typed until the receiver acknowledges the previous packet. Then the second, larger packet is sent, and the additional typed characters are saved until the acknowledgment comes back. The effect is to accumulate characters into larger chunks, and pace their transmission to the network at a rate matching the round-trip time of the given connection. This method is usually preferable for all TCP-based traffic.
By default, the Nagle algorithm is not enabled.
Switching and Scheduling Priorities
The normal operation of the network server allows the switching operations to use as much of the central processor as required. If the network is running unusually heavy loads that do not allow the processor the time to handle the routing protocols, you may need to give priority to the system process scheduler.
System Buffer Size
You can adjust the initial buffer pool settings and limits at which temporary buffers are created and destroyed.
During normal system operation, there are two sets of buffer pools: public and interface. They behave as follows:
- The buffers in the public pools grow and shrink based upon demand. Some public pools are temporary and are created and destroyed as needed. Other public pools are permanently allocated and cannot be destroyed. Public buffer pools are labeled as small, middle, big, very big, large, and huge.
- Interface pools are static--that is, they are all permanent. One interface pool exists for each interface. For example, a Cisco 4000 1E 4T configuration has one Ethernet buffer pool and four serial buffer pools.
The server has one pool of queueing elements and six public pools of packet buffers of different sizes. For each pool, the server keeps count of the number of outstanding buffers, the number of buffers in the free list, and the maximum number of buffers allowed in the free list.
How to Perform Basic System Management
Setting Basic System Parameters
To set basic system parameters perform the following steps. You can perform these steps based on the customization requirements of your system.
DETAILED STEPS
Configuration Examples for Performing Basic System Management
There are no configuration examples for the Performing Basic System Management feature.
Additional References
Related Documents
Related Topic |
Document Title |
---|---|
Cisco IOS commands |
|
Network Management commands |
Cisco IOS Network Management Command Reference |
Cisco IOS fundamental configuration commands |
Cisco IOS Configuration Fundamentals Command Reference |
Cisco IOS fundamental configurations |
Cisco IOS Configuration Fundamentals Configuration Guide |
Preventing UDP diagnostic port attacks |
Defining Strategies to Protect Against UDP Diagnostic Port Denial of Service Attacks |
DHCP configuration |
Cisco IOS IP Addressing Configuration Guide |
Standards
Standard |
Title |
---|---|
None |
-- |
MIBs
MIB |
MIBs Link |
---|---|
None |
To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL: |
RFCs
RFC |
Title |
---|---|
RFC 896 |
Congestion Control in IP/TCP Internetworks |
RFC 951 |
Algorithms for Synchronizing Network Clocks |
RFC 1288 |
The Finger User Information Protocol |
RFC 1534 |
Interoperation Between DHCP and BOOTP |
RFC 2131 |
Dynamic Host Configuration Protocol |
Technical Assistance
Description |
Link |
---|---|
The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password. |
Feature Information for Performing Basic System Management
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 1 | Feature Information for Performing Basic System Management |
Feature Name |
Releases |
Feature Information |
---|---|---|
Performing Basic System Management |
10.0 |
This module describes the basic tasks to manage the general system features of the Cisco IOS software. |
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Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.