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Wednesday, January 28, 2009

Perintah-Perintah Cisco System



Router#show interfaces
Router#show ip protocols
Router#show ip route
Router#show ip arp

3.1 Global configuration (config)

To configure any feature of the router, you must enter configuration mode. This is the first sub-mode of the parent mode. In the parent mode, you issue the command config.

As demonstrated above, the prompt changes to indicate the mode that you are now in.

In connfiguration mode you can set options that apply system-wide, also refered to as "global configurations." For instance, it is a good idea to name your router so that you can easily identify it. You do this in configuration mode with the hostname command.
Router(config)#hostname ExampleName

As demonstrated above, when you set the name of the host with the hostname command, the prompt immediately changes by replacing Router with ExampleName. (Note: It is a good idea to name your routers with an organized naming scheme.)

Another useful command issued from config mode is the command to designate the DNS server to be used by the router:
ExampleName(config)#ip name-server aa.bb.cc.dd

This is also where you set the password for privileged mode.
ExampleName(config)#enable secret examplepassword

Until you hit ctrl-Z (or type exit until you reach parent mode) your command has not been put into affect. You can enter config mode, issue several different commands, then hit ctrl-Z to activate them all. Each time you hit ctrl-Z you return to parent mode and the prompt:

Here you use show commands to verify the results of the commands you issued in config mode. To verify the results of the ip name-server command, issue the command show host.
3.2 Configuring Cisco router interfaces

Cisco interface naming is straightforward. Individual interfaces are referred to by this convention:
media type slot#/port#

"Media type" refers to the type of media that the port is an interface for, such as Ethernet, Token Ring, FDDI, serial, etc. Slot numbers are only applicable for routers that provide slots into which you can install modules. These modules contain several ports for a given media. The 7200 series is an example. These modules are even hot-swapable. You can remove a module from a slot and replace it with a different module, without interrupting service provided by the other modules installed in the router. These slots are numbered on the router.

Port number refers to the port in reference to the other ports in that module. Numbering is left-to-right, and all numbering starts at 0, not at one.

For example, a Cisco 7206 is a 7200 series router with six slots. To refer to an interface that is the third port of an Ethernet module installed in the sixth slot, it would be interface ethernet 6/2. Therefor, to display the configuration of that interface you use the command:
ExampleName#show interface ethernet 6/2

If your router does not have slots, like a 1600, then the interface name consists only of:
media type port#

For example:
ExampleName#show interface serial 0

Here is an example of configuring a serial port with an IP address:
ExampleName(config)#interface serial 1/1
ExampleName(config-if)#ip address
ExampleName(config-if)#no shutdown

Then to verify configuration:
ExampleName#show interface serial 1/1

Note the no shutdown command. An interface may be correctly configured and physically connected, yet be "administratively down." In this state it will not function. The command for causing an interface to be administratively down is shutdown.
ExampleName(config)#interface serial 1/1
ExampleName#show interface serial 1/1

In the Cisco IOS, the way to reverse or delete the results of any command is to simply put no infront of it. For instance, if we wanted to unassign the IP address we had assigned to interface serial 1/1:
ExampleName(config)#interface serail 1/1
ExampleName(config-if)#no ip address
ExampleName#show interface serial 1/1

Configuring most interfaces for LAN connections might consist only of assigning a network layer address and making sure the interface is not administratively shutdown. It is usually not necessary to stipulate data-link layer encapsulation. Note that it is often necessary to stipulate the appropriate data-link layer encapsulation for WAN connections, such as frame-relay and ATM. Serial interfaces default to using HDLC. A discussion of data-link protocols is outside the scope of this document. You will need to look up the IOS command encapsulation for more details.
3.3 Configuring Cisco Routing

IP routing is automatically enabled on Cisco routers. If it has been previously disabled on your router, you turn it back on in config mode with the command ip routing.
ExampleName(config)#ip routing

There are two main ways a router knows where to send packets. The administrator can assign static routes, or the router can learn routes by employing a dynamic routing protocol.

These days static routes are generally used in very simple networks or in particular cases that necessitate their use. To create a static route, the administrator tells the router operating system that any network traffic destined for a specified network layer address should be forwarded to a similiarly specified network layer address. In the Cisco IOS this is done with the ip route command.
ExampleName(config)#ip route
ExampleName#show ip route

Two things to be said about this example. First, the packet destination address must include the subnet mask for that destination network. Second, the address it is to be forwarded to is the specified addres of the next router along the path to the destination. This is the most common way of setting up a static route, and the only one this document covers. Be aware, however, that there are other methods.

Dynamic routing protocols, running on connected routers, enable those routers to share routing information. This enables routers to learn the routes available to them. The advantage of this method is that routers are able to adjust to changes in network topologies. If a route is physically removed, or a neighbor router goes down, the routing protocol searches for a new route. Routing protocols can even dynamically choose between possible routes based on variables such as network congestion or network reliability.

There are many different routing protocols, and they all use different variables, known as "metrics," to decide upon appropriate routes. Unfortunately, a router needs to be running the same routing protocols as its neighbors. Many routers can, however, run mutliple protocols. Also, many protocols are designed to be able to pass routing information to other routing protocols. This is called "redistribution." The author has no experience with trying to make redistribution work. There is an IOS redistribute command you can research if you think this is something you need. This document's compagnion case study describes an alternative method to deal with different routing protocols in some circumstances.

Routing protocols are a complex topic and this document contains only this superficial description of them. There is much to learn about them, and there are many sources of information about them available. An excelent source of information on this topic is Cisco's website, http://www.cisco.com.

This document describes how to configure the Routing Information Protocol (RIP) on Cisco routers. From the command-line, we must explicitly tell the router which protocol to use, and what networks the protocol will route for.
ExampleName(config)#router rip
ExampleName(config-router)#network aa.bb.cc.dd
ExampleName(config-router)#network ee.ff.gg.hh
ExampleName#show ip protocols

Now when you issue the show ip protocols command, you should see an entry describing RIP configuration.
3.4 Saving your Cisco Router configuration

Once you have configured routing on the router, and you have configured individual interfaces, your router should be capable of routing traffic. Give it a few moments to talk to its neighbors, then issue the commands show ip route and show ip arp. There should now be entries in these tables learned from the routing protocol.

If you turned the router off right now, and turned it on again, you would have to start configuration over again. Your running configuration is not saved to any perminent storage media. You can see this configuration with the command show running-config.
ExampleName#show running-config

You do want to save your successful running configuration. Issue the command copy running-config startup-config.
ExampleName#copy running-config startup-config

Your configuration is now saved to non-volatile RAM (NVRAM). Issue the command show startup-config.
ExampleName#show startup-config

Now any time you need to return your router to that configuration, issue the command copy startup-config running-config.
ExampleName#copy startup-config running-config
3.5 Example Cisco Router configuration

1. Router>enable
2. Router#config
3. Router(config)#hostname N115-7206
4. N115-7206(config)#interface serial 1/1
5. N115-7206(config-if)ip address
6. N115-7206(config-if)no shutdown
7. N115-7206(config-if)ctrl-z
8. N115-7206#show interface serial 1/1
9. N115-7206#config
10. N115-7206(config)#interface ethernet 2/3
11. N115-7206(config-if)#ip address
12. N115-7206(config-if)#no shutdown
13. N115-7206(config-if)#ctrl-z
14. N115-7206#show interface ethernet 2/3
15. N115-7206#config
16. N115-7206(config)#router rip
17. N115-7206(config-router)#network
18. N115-7206(config-router)#network
19. N115-7206(config-router)#ctrl-z
20. N115-7206#show ip protocols
21. N115-7206#ping
22. N115-7206#config
23. N115-7206(config)#ip name-server
24. N115-7206(config)#ctrl-z
25. N115-7206#ping archie.au
26. N115-7206#config
27. N115-7206(config)#enable secret password
28. N115-7206(config)#ctrl-z
29. N115-7206#copy running-config startup-config
30. N115-7206#exit

4. Troubleshooting your Cisco router

Inevitably, there will be problems. Usually, it will come in the form of a user notifying you that they can not reach a certain destination, or any destinattion at all. You will need to be able to check how the router is attempting to route traffic, and you must be able to track down the point of failure.

You are already familiar with the show commands, both specific commands and how to learn what other show commands are available. Some of the most basic, most useful commands you will use for troubleshooting are:
ExampleName#show interfaces
ExampleName#show ip protocols
ExampleName#show ip route
ExampleName#show ip arp
4.1 Testing connectivity

It is very possible that the point of failure is not in your router configuration, or at your router at all. If you examine your router's configuration and operation and everything looks good, the problem might be be farther up the line. In fact, it may be the line itself, or it could be another router, which may or may not be under your administration.

One extremely useful and simple diagnostic tool is the ping command. Ping is an implementation of the IP Message Control Protocol (ICMP). Ping sends an ICMP echo request to a destination IP address. If the destination machine receives the request, it responds with an ICMP echo response. This is a very simple exchange that consists of:

Hello, are you alive?

Yes, I am.
ExampleName#ping xx.xx.xx.xx

If the ping test is successful, you know that the destination you are having difficulty reaching is alive and physically reachable.

If there are routers between your router and the destination you are having difficulty reaching, the problem might be at one of the other routers. Even if you ping a router and it responds, it might have other interfaces that are down, its routing table may be corrupted, or any number of other problems may exist.

To see where packets that leave your router for a particular destination go, and how far, use the trace command.
ExampleName#trace xx.xx.xx.xx

It may take a few minutes for this utility to finish, so give it some time. It will display a list of all the hops it makes on the way to the destination.
4.2 debug commands

There are several debug commands provided by the IOS. These commands are not covered here. Refer to the Cisco website for more information.
4.3 Hardware and physical connections

Do not overlook the possibility that the point of failure is a hardware or physical connection failure. Any number of things can go wrong, from board failures to cut cables to power failures. This document will not describew troubleshooting these problems, except for these simple things.

Check to see that the router is turned on. Also make sure that no cables are loose or damaged. Finally, make sure cables are plugged into the correct ports. Beyond this simple advice you will need to check other sources.
4.4 Out of your control

If the point of failure is farther up the line, the prolem might lie with equipment not under your administration. Your only option might be to contact the equipment's administrator, notify them of your problem, and ask them for help. It is in your interest to be courtious and respectful. The other administrator has their own problems, their own workload and their own priorities. Their agenda might even directly conflict with yours, such as their intention to change dynamic routing protocols, etc. You must work with them, even if the situation is frustrating. Alienating someone with the power to block important routes to your network is not a good idea.
5. References

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