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Figure 3-5 HTTP Web Page on a Cisco Router

HTTP options; simply click to expand IOS command set.

Help Options

NOTE The command to disable HTTP server on a Cisco router is no ip http server. To set username/password pairs, use the following IOS command:

username username privilege [0-15] password password

You can also define the HTTP port number with the following command:

ip http [0-65535]

The default is 80.

Secure Socket Layer

Secure Socket Layer (SSL) is an encryption technology for web host devices used to provide secure transactions. For example, a secure transaction is required when clients enter their credit card numbers for e-commerce via their browser. When the end user enters a web address via an Internet browser, such as Internet Explorer, instead of entering HTTP: //web address in the address window, the end user enters HTTPS://web address.

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Table 3-1 describes this syntax.

SNMP servers collect information from remote devices known as SNMP agents. SNMP packets are sent and received by devices on UDP ports 161 (SNMP servers) and 162 (SNMP agents).

The Management Information Base (MIB) is a virtual information storage area for network management information consisting of collections of managed objects. Within the MIB are collections of related objects, defined in MIB modules. MIB modules are written in the SNMP MIB module language, as defined in STD 58, RFC 2578, RFC 2579, and RFC 2580. SNMP port 161 is used to query SNMP devices, and SNMP port 162 is used to send SNMP traps. SNMP runs over UDP and is secured by a well-known, case-sensitive community string.

SNMP Notifications

SNMP’s key feature is the ability to generate notifications from SNMP agents.

Cisco routers can be configured to send SNMP traps or informed requests to a Network Management System (NMS) where a network administrator can view the data.

Figure 3-6 displays the typical communication between an SNMP manager and the SNMP agent (for example, a Cisco-enabled SNMP router).

Unsolicited notifications can be generated as traps or inform requests. Traps are messages alerting the SNMP manager to a condition on the network (sent by the SNMP agent). Inform requests (informs) are traps that include a request for confirmation of receipt from the SNMP manager. SNMP notifications can indicate improper user authentication, restarts, the closing of a connection, loss of connection to a neighbor router, or other significant events.

NOTE Managed devices are monitored and controlled using three common SNMP commands: read, write, and trap.

The read command is used by an NMS to monitor managed devices. The NMS examines different variables that are maintained by managed devices.

The write command is used by an NMS to control managed devices. The NMS changes the values of variables stored within managed devices.

The trap command is used by managed devices to asynchronously report events to the NMS. For example, Cisco IOS routers can be configured to report errors, such as emergencies alerts, to the NMS for urgent action, such as low memory resources or unauthorized access. When certain types of events occur, a managed device sends a trap to the NMS.

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Management Information Base (MIB), a database of network management information, is used and maintained by a management protocol such as SNMP. The value of an MIB object can be changed or retrieved using SNMP commands, usually through a GUI network management system. Cisco supports a number of defined and proprietary MIB commands.

If the snmp-server community command is not used during the SNMP configuration session, it will automatically be added to the configuration after the snmp-server host command is used. In this case, the default password (string) for the snmp-server community is taken from the snmp-server host command. You must always set the community string manually; otherwise, your router could be left vulnerable to SNMP get commands.

Example 3-7 configures a Cisco IOS router for SNMP support.

Example 3-7 Sample SNMP Configuration

snmp-server community public RO snmp-server enable traps config snmp-server host 131.108.255.254 isdn

The IOS command snmp-server community public RO enables SNMP on a Cisco router. This command is also used to restrict access via SNMP. The community string is defined as public and acts as a password protection mechanism against unauthorized users. The community string is sent in every SNMP packet, so an incorrect community string results in no authorized access to the SNMP agent. The read-only attribute means that no configuration changes will be permitted via an SNMP.

The IOS command snmp-server enable traps config advises the NMS of any configuration changes. The IOS command snmp-server host 131.108.255.254 isdn alerts the host 131.108.254.254 of any ISDN traps. ISDN traps can include link flapping or high link usage, for example. (See Table 3-2 for a comprehensive list of traps.)

To specify the recipient of an SNMP notification operation, use the snmp-server host global configuration command. To remove the specified host, use the no form of this command.

snmp-server host host-addr [traps | informs] [version {1 | 2c | 3

[auth | noauth | priv]}] community-string [udp-port port] [notification-type]

Table 3-3 expands the snmp-server host IOS command and presents the full range of options, including MD5 authentication.