There are ten Cisco IOS commands that every Cisco network engineer need to know. These are essential administration and troubleshooting commands that you will use every day when configuring and maintaining today’s complex networks. You may already know these commands but whether you are a seasoned veteran or brand new to networking you should commit these commands and there functions to memory.
show running-config: With the show running-config command, you see the router’s or switch’s entire running- config, this is the configurations that is copied into memory from the startup-config during the boot process. It containes the IP addresses, interfaces, passwords (if stored in clear text), routing protocols, and other settings. This command can be abbreviated sh ru (show run) or wr t (write terminal).
show ip interface: This command is used to display what interfaces are on your router or switch, and the important statistics about those interfaces, and whether they are up or down. This command can be abbreviated as sh int.
The show interfaces command is a very verbose command that provides a lot of output so there are a couple of options the can be added to this command to filter the output, they are as follows:
show ip interface [type number]: This displays on the information for the selected interface.
Show ip interface [brief ]: Displays a summary of the usability status information for each interface.
These two options can be combined show ip interface [type number][brief] to display only the summary information for a given interface.
show ip route: This command displays the routing information for each interface. With this command you can display the routing protocol used for each learned and static route the administrative distance and metric for each route. This command is very useful when trying to troubleshoot reachability problems. This command can be abbreviated as sh ip ro.
copy running-config startup-config: This command is used to save your configuration changes. This command copies the running configuration to the startup configuration in flash. By copying it to flash, it will be saved when the router is powered off and restarted.
show cdp neighbor: This command is used to display all the connected Cisco devices. It will display the type of device connected, the local and remote interface along with the hold time. Very useful when troubleshooting connectivity issues or exploring an unknown connection. This command can be abbreviated as sh cdp ne.
ping: The ping command is a very common method for troubleshooting the accessibility of devices. It uses a series of Internet Control Message Protocol (ICMP) Echo messages to determine:
- Whether a remote host is active or inactive.
- The round-trip delay in communicating with the host.
- Packet loss.
traceroute: The traceroute command is used to discover the routes that packets actually take when traveling to their destination. The device (for example, a router or a PC) sends out a sequence of User Datagram Protocol (UDP) datagrams to an invalid port address at the remote host.
Three datagrams are sent, each with a Time-To-Live (TTL) field value set to one. The TTL value of 1 causes the datagram to “timeout” as soon as it hits the first router in the path; this router then responds with an ICMP Time Exceeded Message (TEM) indicating that the datagram has expired.
Another three UDP messages are now sent, each with the TTL value set to 2, which causes the second router to return ICMP TEMs. This process continues until the packets actually reach the other destination. Since these datagrams are trying to access an invalid port at the destination host, ICMP Port Unreachable Messages are returned, indicating an unreachable port; this event signals the Traceroute program that it is finished.
The purpose behind this is to record the source of each ICMP Time Exceeded Message to provide a trace of the path the packet took to reach the destination. For all the options about this command,
show ip protocols: This command is used to display the parameters and current state of the active routing protocol process. The information displayed by the show ip protocols command is useful in debugging routing operations. Information in the Routing Information Sources field of the show ip protocols output can help you identify a router suspected of delivering bad routing information. This command can be abbreviated as sh ip prot.
show arp: This command displays the IP and MAC address of each enabled interface.
show version: This command displays information about the currently loaded software along with hardware and device information such as the size of the RAM and FLASH installed. This command can be abbreviated as sh ver.
Configuring and troubleshooting Cisco routers and switches is all about knowing what Cisco IOS command to type in order to get the results you need. The 10 commands shown in this article are just a few of the thousands of possible Cisco IOS commands. However, these commands are some of the core commands that every network engineer should know.