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]
[OK]
Erase of nvram: complete
Todd#
*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
Todd#reload
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 192.168.1.33/27
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]
Router#
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 192.168.1.33/27
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 1.1.1.1/24
Broadcast address is 255.255.255.255
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 100.30.31.5/24
Serial0/1 is administratively down, line protocol is down
Serial0/2 is up, line protocol is up
Internet address is 100.50.31.2/24
Loopback0 is up, line protocol is up
Internet address is 100.20.31.1/24
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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