The Cisco Internetwork Operating System (IOS) is one of the most important tools that you have at your disposal as an administrator. It is the core of all Cisco routers and switches, so it’s not just some tool to run a few commands on; it’s the most important thing in your network. If you don’t know how to use it, you are likely doing more harm than good when trying to make changes and fix problems on your network devices.
If you’re new to working with the Cisco IOS, there are a few commands that you should master in order to make your life easier. In this blog post, we’ll go over 10 of those commands. These include creating basic templates and using them for configuring more complex features on devices. We’ll also cover how to filter output and show only what you need as well as how to troubleshoot network problems by checking statistics at various points along the network path.
Basic Router Security
One of the most important things you can do to secure your router is to change the default password. Attackers know the default passwords for many routers, so it’s important to pick a new, strong password that they won’t be able to guess.
Common Syslog Messages
When working with the Cisco IOS, it is important to know the common syslog messages that you may see. These messages can help you troubleshoot and identify issues with your network. Here are 10 of the most common syslog messages – Failure (system failure)
- Terminated (connection terminated)
- Reset (connection reset)
- Busy (port busy)
- Open or Close Pending or Dialing Outbound Calling Attempts Dropped (outbound call dropped because destination not reached)
- Connection Reset by Peer(local link was reset by a peer device on the other end of the connection) – Line Protected from Incoming Calls (the line cannot be used for incoming calls because an outgoing call is in progress)
- DTE Communication Lost (dial-up link lost)
- Prematurely Disconnected due to Link Failure: Automatic Retry in Progress (A technician has attempted to reconnect but has not yet been successful)
- Unsuccessful Modem Handshake (modem did not negotiate a protocol agreement during handshake sequence)
- Voice Switched Analog Call Initiated – Failed Transfer Switchover (voice switched analogue call initiated; failed transfer switchover). – Call Cleared (call cleared).
- Idle Condition on Trunk Group Verified at DMM Level – Informational Message: A trunk group contains no active circuits.
- Connected Data Circuit Switched Connection Number 2F4336E2/6009.
Configure Interface Loopback on Routers
One of the most important commands when working with the Cisco IOS is the configure interface loopback command. This command allows you to configure an interface on a router so that it can be used as a loopback interface. This is useful for troubleshooting and for creating virtual interfaces. To use this command, enter configure terminal followed by config-if where the config-if stands for configuration of an interface. Next, type ip address followed by the IP address of your interface in one line without any spaces. Finally, type no shutdown at the end to activate your new loopback interface on your router.
Enable SSH On Cisco Router
If you want to remotely access your Cisco router, you’ll need to enable SSH. This can be done with just a few simple steps:
- Enter global configuration mode by typing in config t
- Type in ip ssh version 2
- Type in line vty 0 4
- In line configuration mode, type in transport input ssh
Debug Command In Real Time On Cisco Router
If you’re troubleshooting a network issue on a Cisco router, the debug command is your best friend. This command lets you see what’s happening on the router in real-time, which can be invaluable when trying to track down a problem. For example, if you want to watch for FTP traffic coming from an internal host or waiting for replies from DNS servers, use this command:
debug ip ftp interface inside; Debug Command On Cisco Router: Another great debugging tool is the show commands line at the bottom of every router’s configuration. Whenever someone makes a change to any configuration line and they want to verify it has taken effect, they need only type show commands and hit enter.
Useful show Commands On Cisco Router
If you want to know what’s going on with your router, these are the show commands you should master. Show commands give you a detailed view of the status and configuration of your router.
- show version – This command displays information about the IOS version, the uptime of the router, how the router booted (e.g., from flash or NVRAM), the type of processor in use, and how much memory is installed.
- show running-config – Displays the contents of the current running configuration file.
- show startup-config – Displays the contents of the startup configuration file, which contains all the commands that will be executed when an interface goes up or down.
- show interfaces – Shows all interfaces as well as their protocol, address/mask, administrative state (up/down), and line protocol state (up/down).
- show ip interface brief – Shows a list of IP interfaces and their corresponding MAC addresses.
Discover MAC Address Table On A VLAN
To find the MAC address table on a VLAN, you’ll need to use the show mac address-table command. This will give you a list of all the MAC addresses on that particular VLAN, as well as the IP address and interface associated with each one.
How To Modify ARP Timeout Value On A Router
If you’re working with the Cisco IOS, it’s important to know how to modify the ARP timeout value on a router. After reading this blog post, hopefully you’ll be able to complete the following commands and edit an ARP time-out value from 300 seconds to 120 seconds:
IOU#configure terminal IOU(config)#ip arp timeout 120 IOU(config) #exit IOU#copy running-config startup-config IOU#show ip arp detail (displays an ARP entry) IOU#ping 10.1.1.2 (to test the ARP changes)
After you set up and verify your ARP change, remember to go back and save it using copy running-config startup-config . If you don’t, you’ll have to wait for your time out value to expire before trying again!