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CCENT™ (Cisco Certified Entry Network Technician) Certification Exam Notes

D. Router commands

1. Key word: COPY <source> <destination>
This command copies configuration information to specified location. The following are some frequently used COPY commands:
· COPY RUNNING-CONFIGURATION STARTUP-CONFIGURATION (alternatively, you can use an older version of the command, WRITE MEMORY): This command saves the current configuration to NVRAM.
Alternatively, we can issue the command using short form:
· COPY RUNNING STARTUP - Copies configuration from RAM to NVRAM
· COPY STARTUP RUNNING - This command merges configuration from NVRAM to RAM.
· COPY FLASH TFTP - Copies current IOS from router flash memory to TFTP server.
· COPY TFTP FLASH - Copies image file from TFTP server to flash. This is used to upgrade the IOS image file to a newer version, or if your IOS image becomes corrupt.

2. "sh int <interface_no> " is a very useful command. It displays the following information:
1. Hardware address
2. Status of interface and the line protocol - carrier detect brings up the serial port(which means that physical layer connections are working) and keep alive bring up the line protocol (which means that Data link layer protocol is working)..
3. MTU, BW, DLY, rely, and load metrics.
4. Encapsulation type (layer 2, Data link layer) - HDLC is the default.

3. SHOW command is extensively used for seeing the status and configuration information of the router. Some of the frequently used commands are:

1. SHOW RUNNING-CONFIGURATION -This command displays the router's active configuration file, passwords, system name, and interface settings, interfaces IP addresses etc.
2. SHOW INTERFACE - Shows status and configuration information of the local interfaces. The first line says something like “TokenRing1 is up, line protocol is up”. The first part “TokenRing1 is up” describes the physical layer components such as electrical cabling and signaling are OK. The second part “line protocol is up” means that the router is detecting keep-alive messages. The router may be put into administratively down status, at which point the line would read, “TokenRing1 is administratively down, line protocol is down.”
3. SHOW INTERFACE SERIAL 0 - Shows the serial 0 configuration.
4. SHOW INTERFACES - Displays statistics for all interfaces configured on the switch.
5. SHOW PROCESS - Displays a router’s CPU utilization.
6. SHOW CONFIG - Displays information on the startup configuration.
7. SHOW VERSION - Displays information about the system hardware (RAM/ROM), software version, names of configuration files, and boot-images. This command will also show the current configuration register value.
8. Show IP protocol: This command will show information on RIP timers including routing update timer (30sec default), hold-down timer (default 180sec). It also displays the number of seconds due for next update (this is fraction of update timer). This command also gives the network number for which IP RIP is enabled, Gateway, and the default metric.
Show IP route: This command will display the IP routing table entries. In addition, it displays the Gateway of last resort (if one is assigned). It also displays the codes used for various types of routes. Some of the important codes are:
C: directly connected;
S: Statically connected
show IP interface: This command shows you interface-wise information such as IP address assigned to each interface, whether the interface is up, MTU etc.
Debug IP RIP: Debug IP RIP will turn the RIP debugging ON. This will display a continuous list of routing updates as they are sent and received. This leads to lot of overhead, which is the reason that you use "undebug ip rip" to turn-off debugging as soon as you finish with debugging.
9. show version: This command displays the current version of the Cisco IOS. In addition, this command displays the following important information:
- How long the router has been up (length of time since boot-up).
- How the system was started (power on etc.)
- From where the system was loaded from (booted via flash , or tftp etc.)
- The contents of configuration register.
10. sh hosts ---> displays the host names and related IP addresses.
11. sh int s0 ---> Among other things, you can see the encapsulation type (layer 2) used.

4. The auxiliary password is used to set the password for the auxiliary port. Assuming that you are at # prompt, the sequence of commands are:

1. RouterA#config t
2. RouterA(config)#line aux 0
3. RouterA(config-line)#login
4. RouterA(config-line)#password <password>
Now you are set with a password <password>. Type "<ctrl>Z " to take you to the # prompt or "exit" to go back to global configuration "RouterA(config)#" prompt.
Similar procedure is applicable for setting vty and console passwords as well.

5. A banner is displayed whenever anyone logs in to your Cisco router. The syntax for configuring the banner is
· "banner motd # " . MOTD stands for "Message Of The Day".
# symbol signifies the start of the banner message to the router. You will be prompted for the message to be displayed. You need to enter "#" symbol at the end of the message, signifying that the msg has ended.

There are five different types of passwords:
1. ENABLE PASSWORD - A global command that restricts access to privileged exec mode. This is a non-encrypted password.
2. ENABLE SECRET - Assigns a one-way encryptographic secret password, available in versions 10.3 and up. This secret password is used instead of the enable password when it exists.
3. Virtual Terminal Password (vty password): The virtual terminal password is used for Telnet sessions into the router. The password can be changed at any time. It can be set up when you configure the router from the console. There can be five distinct passwords corresponding to each vty (vty0 to vty4) or there can be a single password for all vty’s.
4. Auxiliary Password: Auxiliary password is used to set password to the auxiliary port. This port is used to access a router through a modem.
5. Console Password: Console password is used to set the console port password.

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