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To clear a vty (ssh/telnet) connection on Cisco router we have to clear the specific line.
To find this line we can use the following command:

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router#who

For example a router has a vty connection from a host with ip 10.10.10.10 on line 3:
router#who
Line User Host(s) Idle Location
2 vty 1 idle 00:00:02 10.11.10.11
3 vty 2 root idle 00:00:06 10.10.10.10
* 5 vty 4 admin idle 00:00:00 192.168.17.67

Interface User Mode Idle ...

RIP Timers

In addition to the update timer (default 30 sec), the IOS implements three additional timers for RIP:
Invalid
Flush
Holddown

Invalid Timer. If an update has not been received to refresh an existing route after 180 seconds (the default), the route is marked as invalid by setting the metric to 16. The route is retained in the routing table until the flush timer expires.

Flush Timer. By default, the flush timer is set ...

Default administrative distance values

Let's introduce three routing table principles, as described by Alex Zinin in his book, Cisco IP Routing.

Principle 1: "Every router makes its decision alone, based on the information it has in its own routing table."
Principle 2: "The fact that one router has certain information in its routing table does not mean that other routers have the same information."
Principle 3: "Routing information about a path from one network to another does not ...

If you need to disable CDP globally, for the entire device, use this command:

Router(config)#no cdp run

If you want to use CDP but need to stop CDP advertisements on a particular interface, use this command:

Router(config-if)#no cdp enable

The IOS often sends unsolicited messages similar to the changed state to up messages. The IOS message does not affect the command, but it can cause you to lose your place when typing.

Logging Synchronous

In order to keep the unsolicited output separate from your input, enter line configuration mode for the consoled port and add the logging synchronous command, as shown. You will see that messages returned by IOS no longer interfere with your ...

Basic Router Configuration

The first prompt appears at user mode. User mode allows you to view the state of the router, but does not allow you to modify its configuration. Do not confuse the term "user" as used in user mode with users of the network. User mode is intended for the network technicians, operators, and engineers who have the responsibility to configure network devices.

Router>

The enable command is used to enter the privileged ...

Extended Ping

To examine this the IOS offers an "extended" mode of the ping command. This mode is entered by typing ping in privileged EXEC mode, at the CLI prompt without a destination IP address. A series of prompts are then presented as shown in this example. Pressing Enter accepts the indicated default values.

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Router#ping
Protocol [ip]:
Target IP address:10.0.0.1
Repeat count [5]:
Datagram size [100]:
Timeout in seconds [2]:5
Extended commands [n]: n

Entering ...

Backing Up Configurations Offline

Configuration files should be stored as backup files in the event of a problem. Configuration files can be stored on a Trivial File Transfer Protocol (TFTP) server, a CD, a USB memory stick, or a floppy disk stored in a safe place. A configuration file should also be included in the network documentation.

Backup Configuration on TFTP Server

As shown in the figure, one option is to save the running configuration ...

Encrypting Password Display

Another useful command prevents passwords from showing up as plain text when viewing the configuration files. This is the service password-encryption command.

This command causes the encryption of passwords to occur when a password is configured. The service password-encryption command applies weak encryption to all unencrypted passwords. This encryption does not apply to passwords as they are sent over media only in the configuration. The purpose of this command is to keep ...