Nov 18, 2011

Abstract of CCNA study guide-15 -Cisco IOS Basic configurations 4

Continue the series of  Abstract CCNA study guide book .
Viewing, Saving, and Erasing Configurations
You can manually save the file from DRAM to NVRAM by using the copy running-config startup-config command (you can use the shortcut copy run start also):
Todd#copy running-config startup-config
Destination filename [startup-config]? [press enter]
Building configuration...
When you see a question with an answer in [], it means that if you just press Enter, you’re choosing the default answer.
Also, when the command asked for the destination filename, the default answer was startup-config.

You can view the files by typing show running-config or show startup-config from privileged mode. The sh run command, which is a shortcut for show running-config, tells us that we are viewing the current configuration:
Todd#show running-config
Building configuration...
Current configuration : 3343 bytes
version 12.4
[output cut]
The sh start command shows us the configuration that will be used the next time the router is reloaded. It also tells us how much NVRAM is being used to store the startup-config file. Here’s an example:
Todd#show startup-config
Using 1978 out of 245752 bytes
version 12.4
[output cut]

Deleting the Configuration and Reloading the Router
You can delete the startup-config file by using the erase startup-config command:
Todd#erase startup-config
Erasing the nvram filesystem will remove all configuration files! Continue? [confirm][enter]
Erase of nvram: complete
*Feb 28 23:51:21.179: %SYS-7-NV_BLOCK_INIT: Initialized the geometry of nvram
Todd#sh startup-config
startup-config is not present
Proceed with reload? [confirm]System configuration has been modified. Save? [yes/no]: n

If you reload or power down and up the router after using the erase startup-config command, you’ll be offered setup mode because there’s no configuration saved in NVRAM.
You can press Ctrl+C to exit setup mode at any time (the reload command can only be used from privileged mode).

Verifying Your Configuration
 show running-config would be the best way to verify your configuration and show startup-config would be the best way to verify the configuration that’ll be used the next time the router is reloaded.

you can verify your configuration with utilities such as Ping , Traceroute and Telnet.

Telnet, FTP, and HTTP are really the best tools because they use IP at the Network layer and TCP at the Transport layer to create a session with a remote host.
Router#telnet ?
WORD IP address or hostname of a remote system
From the router prompt, you just type a hostname or IP address and it will assume you want to telnet—you don’t need to type the actual command, telnet.

Verifying with the show interface Command
The show interfaces command displays the configurable parameters and statistics of all interfaces on a router.
This command is very useful for verifying and troubleshooting router and network issues.
The following output is from my freshly erased and rebooted 2811 router:

Router#sh int f0/0
FastEthernet0/0 is up, line protocol is up
Hardware is MV96340 Ethernet, address is 001a.2f55.c9e8 (bia 001a.2f55.c9e8)
Internet address is
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
[output cut]
first, I’ve got to ask you, What subnet is the FastEthernet 0/0 a member of and what’s the broadcast address and valid host range?  Easy

 The show interfaces command will show you if you are receiving errors on the interface, and it will show you the maximum transmission units (MTUs), bandwidth (BW), reliability (255/255 means perfect!), and load (1/255 means no load).

Have another look to the sh int command
Router#sh int fa0/0
FastEthernet0/0 is up, line protocol is up

The first parameter refers to the Physical layer, and it’s up when it receives carrier detect. The second parameter refers to the Data Link layer, and it looks for keepalives from the connecting end. (Keepalives are used between devices to make sure connectivity has not dropped.)

Here’s an example of where the problem usually is found—on serial interfaces:
Router#sh int s0/0/0
Serial0/0 is up, line protocol is down
If you see that the line is up but the protocol is down, as shown above, you’re experiencing a clocking (keepalive) or framing problem—possibly an encapsulation mismatch. Check the keepalives on both ends to make sure that they match; that the clock rate is set, if needed, and that the encapsulation type is the same on both ends. The output above would be considered a Data Link layer problem.
If you discover that both the line interface and the protocol are down, it’s a cable or interface problem.
The following output would be considered a Physical layer problem:
Router#sh int s0/0/0
Serial0/0 is down, line protocol is down

If one end is administratively shut down:
Router#sh int s0/0/0
Serial0/0 is administratively down, line protocol is down
To enable the interface, use the command no shutdown from interface configuration mode.

Another important configuration to notice is the keepalive, which is 10 seconds by default. Each router sends a keepalive message to its neighbor every 10 seconds, and if both routers aren’t configured for the same keepalive time, it won’t work.
Router#sh int s0/0/0
Serial0/0 is up, line protocol is up
Hardware is HD64570
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set, keepalive set (10 sec)

You can clear the counters on the interface by typing the command clear counters:
Router#clear counters s0/0/0

Verifying with the show ip interface Command
The show ip interface command will provide you with information regarding the layer 3 configurations of a router’s interfaces:
Router#sh ip interface
FastEthernet0/0 is up, line protocol is up
Internet address is
Broadcast address is
Address determined by setup command
MTU is 1500 bytes
Helper address is not set
Directed broadcast forwarding is disabled
Outgoing access list is not set
Inbound access list is not set
Proxy ARP is enabled
Security level is default
Split horizon is enabled
[output cut]
The status of the interface, the IP address and mask, information on whether an access list is set on the interface, and basic IP information are included in this output.

Using the show ip interface brief Command
 The show ip interface brief command is probably one of the most helpful commands that you can ever use on a Cisco router. This command provides a quick overview of the router’s interfaces, including the logical address and status:
Router#sh ip int brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 unassigned YES unset up up
FastEthernet0/1 unassigned YES unset up up
Serial0/0/0 unassigned YES unset up down
Serial0/0/1 unassigned YES unset administratively down down
Serial0/1/0 unassigned YES unset administratively down down
Serial0/2/0 unassigned YES unset administratively down down

Remember, administratively down means that you need to type no shutdown under the
interface. Notice that Serial0/0/0 is up/down, which means that the physical layer is good and
carrier detect is sensed but no keepalives are being received from the remote end. In a nonproduction
network, like the one I am working with, the clock rate isn’t set.

Verifying with the show protocols Command
The show protocols command used to see the status of layers 1 and 2 of  and IP addresses of each interface:
Router#sh protocols
Global values:
Internet Protocol routing is enabled
Ethernet0/0 is administratively down, line protocol is down
Serial0/0 is up, line protocol is up
Internet address is
Serial0/1 is administratively down, line protocol is down
Serial0/2 is up, line protocol is up
Internet address is
Loopback0 is up, line protocol is up
Internet address is

Using the show controllers Command
The show controllers command displays information about the physical interface itself.
It’ll also give you the type of serial cable plugged into a serial port. Usually, this will only be a DTE cable that plugs into a type of data service unit (DSU).
Router#sh controllers serial 0/0
HD unit 0, idb = 0x1229E4, driver structure at 0x127E70
buffer size 1524 HD unit 0, V.35 DTE cable
cpb = 0xE2, eda = 0x4140, cda = 0x4000

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