Nov 18, 2011

Abstract of CCNA study guide-14 -Cisco IOS Basic configurations 3

Continue the series of  Abstract CCNA study guide book .
Router Interfaces
Different routers use different methods to choose the interfaces used on them. For instance, the following command shows a Cisco 2522 router with 10 serial interfaces, labeled 0 through 9:
Router(config)#int serial ?
<0-9> Serial interface number

Then we can choose serial port 5, for example:
Router(config)#int serial 5

The 2522 router has one Ethernet 10BaseT port, and typing interface ethernet 0 can configure that interface, as seen here:

Router(config)#int ethernet ?

<0-0> Ethernet interface number

Router(config)#int ethernet 0

As I showed you above, the 2500 router is a fixed-configuration router. This means that when you buy that model, you’re stuck with that physical configuration.

To configure an interface, we used the interface type number sequence, but with the 2600 and 2800 series routers (actually, any ISR router for that matter), there’s a physical slot in the router, with a port number on the module plugged into that slot. So on a modular router, the configuration would be interface type slot/port, as seen here:
Router(config)#int fastethernet ?
<0-1> FastEthernet interface number
Router(config)#int fastethernet 0
% Incomplete command.
Router(config)#int fastethernet 0?
Router(config)#int fastethernet 0/?
<0-1> FastEthernet interface number

For the ISR series, it’s basically the same, only you get even more options. For example, the built-in FastEthernet interfaces work with the same configuration we used with the 2600 series:
Todd(config)#int fastEthernet 0/?
<0-1> FastEthernet interface number
Todd(config)#int fastEthernet 0/0

But the rest of the modules are different—they use three numbers instead of two. The first 0 is the router itself, and then you choose the slot, and then the port. Here’s an example of a serial interface on my 2811:
Todd(config)#interface serial ?
<0-2> Serial interface number
Todd(config)#interface serial 0/0/?
<0-1> Serial interface number
Todd(config)#interface serial 0/0/0

you should always view a running-config output first so you know what interfaces you have to deal with.

Just understand that if you type interface e0 on a 2500, interface fastethernet 0/0 on a 2600, or interface serial 0/1/0 on a 2800, all you’re doing is choosing an interface to configure, and basically, they’re all configured the same way after that.

Bringing Up an Interface
 You can disable an interface with the command shutdown and enable it with the no shutdown command.

If an interface is shut down, it’ll display administratively down when you use the show interfaces command (sh int for short) or show running-config :
Todd#sh int f0/1
FastEthernet0/1 is administratively down, line protocol is down
[output cut]

All interfaces are shut down by default.
You can bring up the interface with the no shutdown command (no shut for short):
Todd#config t
Todd(config)#int f0/1
Todd(config-if)#no shutdown

Configuring an IP Address on an Interface
To configure IP addresses on an interface, use the ip address command from interface configuration mode:
Todd(config)#int f0/1
Todd(config-if)#ip address
Don’t forget to enable the interface with the no shutdown command.

If you want to add a second subnet address to an interface, you have to use the secondary parameter. If you type another IP address and press Enter, it will replace the existing IP address and mask.
So let’s try it. To add a secondary IP address, just use the secondary parameter:
Todd(config-if)#ip address ?
secondary Make this IP address a secondary address
Todd(config-if)#ip address secondary

I really wouldn’t recommend having multiple IP addresses on an interface because it’s ugly and inefficient.

Using the Pipe
The pipe is used as  output modifier .This pipe ( | ) allows us to wade through all the configurations or other long outputs and get straight to our goods fast. Here’s an example:
Todd#sh run | ?
append                         Append redirected output to URL (URLs supporting append operation only)
begin                Begin with the line that matches
exclude            Exclude lines that match
include                         Include lines that match
redirect            Redirect output to URL
section                         Filter a section of output
tee                    Copy output to URL
Todd#sh run | begin interface
interface FastEthernet0/0
description Sales VLAN
ip address
interface FastEthernet0/1
ip address secondary
ip address

I use it a lot when I am looking at a large routing table to find out whether a certain route is in the
routing table. Here’s an example:
Todd#sh ip route | include
R [120/2] via, 00:00:25, FastEthernet0/0

Serial Interface Commands
Before you configure a serial interface, you need some key information— like knowing that the interface will usually be attached to a CSU/DSU type of device that provides clocking for the line to the router, as I’ve shown in Figure below.

DTE Here you can see that the serial interface is used to connect to a DCE network via a CSU/DSU that provides the clocking to the router interface. But if you have a back-to-back configuration (for example, one that’s used in a lab environment like I’ve shown you in Figure 4.5), one end— the data communication equipment (DCE) end of the cable—must provide clocking!

By default, Cisco routers are all data terminal equipment (DTE) devices, which means that you must configure an interface to provide clocking if you need it to act like a DCE device.
You configure a DCE serial interface with the clock rate command:
Todd#config t
Todd(config)#int s0/0/0
Todd(config-if)#clock rate 1000000
The clock rate command is set in bits per second. Besides looking at the cable end to check for a label of DCE or DTE, you can see if a router’s serial interface has a DCE cable connected with the show controllers int command:
Todd#sh controllers s0/0/0
Interface Serial0/0/0
Hardware is GT96K
DTE V.35idb at 0x4342FCB0, driver data structure at 0x434373D4
Here is an example of an output that shows a DCE connection:
Todd#sh controllers s0/2/0
Interface Serial0/2/0
Hardware is GT96K
DCE V.35, clock rate 1000000

The next command you need to get acquainted with is the bandwidth command.
Here’s an example of using the bandwidth command:
Todd#config t
Todd(config)#int s0/0/0
Todd(config-if)#bandwidth ?
<1-10000000> Bandwidth in kilobits
inherit              Specify that bandwidth is inherited
receive                         Specify receive-side bandwidth
Todd(config-if)#bandwidth 1000
Did you notice that, the bandwidth command is configured in kilobits?

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