Back to the basics: Part 1 Device Access Modes

By KailinAchesonIt is said that Vince Lombardi, the legendary coach, once stood before his team of professional football players, and said, “Gentlemen. This is a football.” This is the starting point, the basics. Today, we will discuss the fundamentals of networking: routers, switches, user EXEC and privileged EXEC modes.
This is the place for you if you are new to the Cisco router and switch scene, are unsure what commands you can enter at different prompts or are unaware that there are many prompts. These concepts will be tested in the ICND1 certification exam. If you want to earn your CCNA or CCENT certification, then read on.
Let’s start with a few brief explanations of the devices.
A switch provides local connectivity between endpoint device. It forwards frames to the correct ports and uses physical addresses such as Media Access Control (MAC), addresses to perform its work. A switch operates at Layer 2 (Data Link layer) of the Open Systems Interconnection Model (OSI). This is a very basic definition but it’s what we are all about today. A switch is usually described in logical topologies as:
Figure 1 – Switch
A router is a device that provides network connectivity between computer networks. It forwards packets to the correct destination networks and uses logical addresses such as Internet Protocol (IP), addresses to do its job. A router operates at Layer 3 of the OSI Model, the Network layer. This is a very basic definition that serves our purpose. A router looks something like this in logical topologies:
Figure 2 – Router
Each of these devices can be connected to using a command-line. There are two levels of access to the command line on Cisco devices. They are called EXEC mode. There are two EXEC modes: user EXEC and privileged EXEC. User EXEC mode represents the initial mode. It is represented by a greater-than sign (>);. For example, on a switch you might see Switch> when you first log in. Privileged EXEC is a mode that is accessible when you issue the enable command. This mode is represented with a pound sign (#), and might appear as Switch#.
Security is the main reason for both modes. The default default mode is User EXEC, which means that anyone could access it. It can be secured so that only authorized users have access to it and can make configuration changes.
User EXEC Mode
Mode of Private EXEC
Is the prompt switch>
Is the prompt Switch#
Is this the default mode?
Access requires the enable command
It is easily accessible, but not as easily secured
It is easy to secure and therefore less accessible
It contains very few commands, including help or show.
It contains a wide range of commands, including show and help.
Configuration changes are not possible
Allows configuration changes and access other modes
The question mark (?) can be used to get an idea of all the commands available for each EXEC mode. command. Figure 3 shows, taken from the Boson Network Simulator, a selection of switch commands available from user EXEC mode.
Figure 3 – User EXEC Mod Switch Commands
Figure 4 shows a selection of switch commands available from privileged EXEC modes:Figure 4 – Private EXEC Mode Switch Commands
You can return to user EXEC by issuing the exit command from privileged EXEC Mode.
You can issue the configure terminal command from privileged EXEC mode to access global configuration mode. From there, you can access additional modes like interface configuration mode or subinterface configuration mode. This blog is about access mode basics so I will save those for another day. You can read more about these modes by returning soon.
Part two is now available here: http://blog.boson.com/bid/87424/Back-to-the-Basics-Device-Access-Mod

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