In order to Troubleshoot quickly and accurately:
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1. What time was it working right?
2. Any new software or feature was added?
3. Any new hardware was added?
4. Any new change or update or program installed?
*Check the Program or enable feature date installed.
*Keep a log and track of changes.
-Then you just need to uninstall it to make it work again.
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Cisco IOS, is base on Unix/Linux operating system.
–When you only know one or two letter of the whole word, you can use the ? mark, no space! You’re searching for a command that began with IN, what command match or begin with IN
example: show ip in?
–If you put a space after a valid command like below, it will show sub command that are available to use.
show ip interface ?
When we dealing with network, it is an IP network.
That is why IP is a key word, it is a main command option.
This will display tons of sub commands under the IP command:
show ip ?
If you don’t include the IP, you are looking for a particular category, not an entire network command listing.
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*To help you move quickly when using Cisco IOS, try pressing: press Tab key, Spacebar, up/down Arrow Key, Home Key, CTRL X, CTRL C, CTRL V, Double click on word then right click to paste. You can also create alias to map to keyboard to by pass typing in a long whole command. Example, instead of typing Conf T you just need to create an alias such as: Shift C
To quit Ping or Traceroute: CTRL Shift 6
To see information about that process: Debug ?
Turn off all debug message. U ALL
What is Flash? It’s RAM flash disk, it is act like a hard disk for the devices to store files.
Running config is a file that load when the devices is bootup. Startup Config files is the running config files that was on the flash disk. So in short Flash is a hard disk space.
Flash store number of files that run the devices and it’s configuration info. If you delete the ISO files then you will have restore from a TFTP server using the console cable only (no ssh or tenet will work!).
But if you delete Running Config or Vlan Database files in the flash and then Reload (reboot) the device it will have a factory default setting, all your config setting is all erased.
*Flash files is compressed, it will uncompressed.
Step to Reset device to factory default settings.
Step 1: reset Vlan Database file to factory setting
Show flash
Delete flash vlan dat
Reload
*You also need to erase all the configuration from the router to factory default. When the device came backup it will has no configuration setting. It’s good for the next class student, so they can learn from scratch.
Step 2: reset Start Up config file to factory setting
Erase startup-config
Reload
-say no, and confirm to erase
-Device will be factory reset after the two above steps.
*updating the firmware is the process of delete the IOS from flash. But you must know the new firmware is compatible! and you must be able to use console cable and load the new ISO from a TFTP server.
—————-
or
Erase everything to factory setting with this command:
(Erase the setup you did to All the config files at once!)
*This will Delete all the vlans and all the setup you did to the device.
erase ?
erase /all nvram:
reload
Bridge in STP (spanning-tree) is referring to the Switch, mean the same thing.
show spanning-tree bri
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How to Save the change?
After you made any changes to the devices. You’ll need to saved it. If you don’t when you reboot the device it will lost all the changed you made. Just type in:
wr
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privilege 15 mean to give full Admin right!
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SHOW command is to find out information of the setting been configure to it.
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When the devices are booting up:
It load the startup-config files from the memory (flash) into RAM, now this files is known as the running-config files. And when you login into the devices you are working with the running-config files.
-Then when you saved the running-config files back into the device into flash and then it overwrite over the old startup-config files in the (flash).
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Line is refer to as how can you connect to that devices: Local attached cable or via network.
——Example below:
SwithA(config)#line ?
<0-102> First Line number
aux Auxiliary line (modem dial-into the device)
console Primary terminal line (Local port in the back of the device)
tty Terminal controller
vty Virtual terminal (virtual port use via Telnet, SSH that allow CLI command to be send to the device)
x/y Slot/Port for Modems
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If you have an issue related to interface is not working right. You can check the Speed, Duplex, MTU setting and show the interface status to see where the issue are. When Two interface are connecting to each others. You can’t set one side to half duplex mode and the other size to full duplex mode, it has to be the same mode… Also the Speed has to be match the same.
SPEED = how fast is the line speed rate at? 10/ 100/ 1000 Mbps / Auto
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Duplex option:
Full Duplex = Switch/Router ports can do both SEND and RECIVED data at the same time.
Haft Duplex = Hub devices only can just only SEND or just only Received one at time. And you can use the following command to check the duplex setting:
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show int status
show int FastEthernet1/5 status
show int FastEthernet1/5
*pay attention to:
Runts
Giants
Intput errors
CRC
Frame
Packet Outputs
Output errors
Collision
reliability 255/255
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To see erase/clear out old info recorded for All of the interfaces.
clear counters
That particular interface:
clear counters FastEthernet1/1
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Firewall subnet or zone explanation:
DMZ zone= server place on DMZ zone it is not protect by the firewall. It place outside of the firewall control. This allow outside access and also internal LAN access. This server is a public server access both by WAN and LAN users.
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ACL (access control list) = what are the permission allow or denied connection rules. It the same concept of user/permission right in Window, but it use: Objects, IP address ranges, Network ID, host ID.
Standard: Identify traffic such as VPN, Route-maps
Extended: use for traffic filtering
EtherType: filter non-IP traffic
WebType: filter traffic on a clientless SSL VPN
Management ACL: filter the managed traffic
Below are some of the most use commands in Cisco IOS operating system:
show history / do sh hi is use to copy code from one device to the next device.
show running-config / sh run: is to show the current setup that is running right now.
show startup-config / sh star: is to show the stored changed in the RAM. You can use to compare the setting between the live setting and the store setting.
show version / sh ver : info about the IOS image is, operating system info.
show etherchannel / sh et : info about port channel setting
show flash / sh fl : all the devices config files
sh int
sh int f1/3
show interfaces status
show interfaces switchport
show interfaces trunk
show ipv6 int
show ipv6 interface brief
show cdp neighbors
show clock
show ntp status
show Flash
conf t
DO show history
show logging
show etherchannel summary
show etherchannel 1 port-channel
show interfaces etherchannel
show protocols
show users
show access-lists
show ip dhcp binding
show ip dhcp pool
show ip eigrp neighbors
show ip ospf neighbor
show ip nat translations
show standby
show tech-support
show processes
show mac address-table
show spanning tree summary
show etherchannel
show vlan
show vtp status
show monitor session all
show interface | include (rate|ethernet0)
Debug ?
u all
Troubleshooting:
is to gather information about the problem first, before trying to guess anything, and let use the OSI model. Then try it out and document it after.
In computer program is all a steps process: It is a steps by step of data request and checking. If the data state if: Yes or No or Boolean value then the program will run or it will not run until the data are met. (Because it is looking for that value data that it was missing and was programed in by the programmer.)
————-The 7 layers of the OSI model program
7. Application = maybe the Software option got changed, or corrupted.
6. Presentation
5. Session
4. Transport =
*Network = router connection issue, show run
2. Data Link =switch, ports, cable bad, show run
1. Physical = plug in with a good cable, bad drop
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Can you Ping it? to see if the device is down or maybe misconfigure somehow.
Can you Traceroute it? to see what router path is down?
Is there any alert of devices issue going on?
-ping the pc, ping the switch, ping the router.
-Then you can traceroute to see what router can see other router.
show cdp
show ip int br
-check ip address if it is correct on those interface and documentation.
(*You can also try SSH or Telnet to the router or switch and see if you can connect to it.)
SSH is more secure, because it scramble the password
Telnet is Not secure, because it doesn’t scramble the password during the login process. And you can use use Wireshark program to see the actual login ID easily.
Troubleshooting part 2: is to gather information only about the problem first, before trying to guess anything, and let use the OSI model. Then try it out and document it after. Gather information start with the software the user is using, then what other software involves are to make this process working.
In computer: You will have always deal with: Files, Folders, programming (task) then send / receive from one PC to the next PC over cable then into Switch then into Router the the reverse happen on the other side that must have the same setting on both side of communication.
In computer program are all a steps taking process. It is a steps by step of data request and checking. If the data state if: Yes or No or Boolean value then the program will run or it will not run until the data are met. (Because it is looking for that value data that it was missing and was programed in by the programmer.)
————-The 7 layers of the OSI model program
7. Application = maybe the Software option got changed, or corrupted.
6. Presentation
5. Session
4. Transport =
*Network = router connection issue, show run
2. Data Link =switch, ports, cable bad, show run
1. Physical = plug in with a good cable, bad drop
———-
Can you Ping it? to see if the device is down or maybe misconfigure somehow.
Can you Traceroute it? to see what router path is down?
Is there any alert of devices issue going on?
-ping the pc, ping the switch, ping the router.
-Then you can traceroute to see what router can see other router.
show cdp
show ip int br
-check ip address if it is correct on those interface and documentation.
(*You can also try ssh or telnet to the router or switch and see if you can connect to it.)
“When it work, it is like magic, but in reality you’re neither tell the program the wrong information or entered the correct information to be use when running that particular feature of the program. A good habit is to make sure you entered it as exactly right into the program to be use, this way you don’t have to re-check you work, after so much. A notepad can be help to document and use to understand each statement line of code does or what it is referencing to.
If you don’t understand each line of statement code. You are likely to miss-configure it. Because you may not get the concept right. That is ok, because it just the way they put this together and we are not use it that way. Computer program is not the same as everyday written language.”
More info and read about other topic:
https://www.linkedin.com/today/author/priyanka-kumari-07b40684?trk=pulse-article_more-articles
Khmer Certified 