Cisco Routers

Cisco Router

Routers produced by Cisco Systems are some of the best, and are certainly the most dominant routers, in the telecommunications industry today. Cisco routers distribute packets of data as a mediary between networks and are the catalyst today providing inter-connectivity and communication world-wide.

Cisco routers come custom tailored for many applications ranging from home use, to the office, to the large enterprise. The documentation contained herein will exclusively focus on Cisco's office to enterprise level series routing solutions. Routers vary by port density, software (iOS), capacity and type of connectivity in some cases.

Cisco router configuration instructions

Configure a Cisco Router

Log into your routers' shell. Most of the time you'll have to press Enter in order to see the routers' command prompt. If it's unconfigured it'll look similar to:

Router>

If you've just switched the router on, after it boots it'll ask if you'd like to begin the initial configuration. Opt for no. If you say yes, you will be subjected to the menu.

Routing Modes

Cisco's IOS software command-line interface is exists based on contrasting interface modes. You'll see lots of contrasting modes while configuring your router, and the mode you're currently in will determine which instructions you'll be able to access. All modes have a set of instructions available in that mode, some of the instructions are exclusive to the mode. However, at any time typing a question-mark(?) will show you a list of the instructions currently available in that mode. This can save you a lot of time, so remember it.

Privledges per mode

When 1st connecting to a Cisco router, you'll be in EXEC mode; the 1st in which you'll be able to issue instructions. In unprivileged mode you use instructions like, show version, display the IOS version this router is currently running. Typing "show ?" will diplay all the show instructions privy within the mode you're residing in.

You will have to enter privledged mode in order to configure the Cisco router. Use the command "enable". Unless your router is completely unconfigured, it should require authentication. Issue the command "enable" and give any passwd required to begin using privileged mode on the router. For your convenience and to prevent confusion, the commandline prompt will change every time you switch modes. For example, when you switch from non-privledged mode into privledged, prompt should change from "Router>" to "Router#".

It's important to note that this prompt change is a valuable tool signifying which mode you're currently working in and It's important to consistently pay mind to what It's and what it changes to.

Within the privileged mode there are several subset modes available to you. Cisco describes two modes, unprivileged and privileged, inclusive of a hierarchy of instructions used in privileged mode. Once you enter parent mode (privledged mode) the command prompt will end with the hash sign (#). There are various other modes You'll use only after being in parent mode. Each has a prompt somewhat like this "Router(arguments)#".

They still all end with the #. They are subsumed within privileged mode. Many of the child-modes have their own children modes and once you begin using priviliged mode, you will gain access to pertinent config info & options the Cisco IOS allows, directly from priviledged, one of the child-modes or the sub-child-modes.

Configuring your Cisco Router

If you've just switched on a completely new Cisco router and It's already configured, you will want to check out the existing configuration. And if it hasn't, you should still become accustomed to the show instructions before beginning the configuration. Begin privileged mode by issuing the command enable, then issue some show instructions to see what they output. Remember, the command show ? will display all the instructions available in the current mode in use. It would be beneficial for you to explore the system and try some of these instructions.

Router#show interfaces
Router#show ip protocols
Router#show ipv6 protocols
Router#show ip route
Router#show ipv6 route
Router#show ip arp
Router#show ipv6 neighbors

When you've begun priviledged mode using "enable", you have entered the top level. It's in the top level where You'll display most the information you need in regard to the router. You should understand by now you do this using the "show" instructions.

Continuing to configure this router; you'll venture into several children modes to set specifications, inevitably returning to the parent mode to display the results of your instructions. You also return to the parent mode to enter other child-modes. To return to the parent mode, now press ctrl-z. This puts any instructions you have just issued into affect, and returns you to parent mode.

Global configuration (config)

To configure any feature of the router, you must enter configuration mode. This is the 1st child-mode of the parent mode. In the parent mode, you issue the command config.

Router#config
Router(config)#

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

In configuration mode You'll set options that apply system-wide, also referred to as "global configurations." For instance, It's a good idea to name your router so that You'll easily identify it. You do this in configuration mode with the hostname command.

Router(config)#hostname ExampleName
ExampleName(config)#

As demonstrated above, when setting the name of the host with the hostname command, prompt immediately changes by replacing Router with ExampleName. (Note: It's 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 bb.cc.dd.ee
ExampleName(config)#ctrl-Z
ExampleName#

This is also where you set the passwd for privileged mode.

ExampleName(config)#enable secret examplepasswd
ExampleName(config)#ctrl-Z
ExampleName#

Until now press ctrl-Z (or type exit until you reach parent mode) your command has not been put into affect. You'll enter config mode, issue several contrasting instructions, then hitctrl-Z to activate them all. Each time now press ctrl-Z you return to parent mode and prompt "ExampleName#"

Here you use show instructions to verify the results of the instructions you issued in config mode. To verify the results of the ip name-server command, issue the command show host.

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, like Ethernet, Token Ring, FDDI, serial, etc. Slot numbers are only applicable for routers that provide slots into which You'll install modules. These modules contain several ports for a given media. The 7200 series is an example. These modules are even hot-swapable. You'll remove a module from a slot and replace it with a contrasting 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 6 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. So 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#

An example being:

ExampleName#show interface serial 0

Then to verify configuration follow these instructions

ExampleName(config)#interface serial 1/1
ExampleName(config-if)#shutdown
ExampleName(config-if)#ctrl-Z
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 192.168.145.2 255.255.255.0
ExampleName(config-if)ctrl-Z
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's usually not necessary to stipulate data-link layer encapsulation. Note that It's often necessary to stipulate the appropriate data-link layer encapsulation for WAN connections, like 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 commandencapsulation for more details.

Configuring for 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
ExampleName(config)#ctrl-Z

To enable IPv6 routing, use the command ipv6 unicast-routing.

ExampleName(config)#ipv6 unicast-routing
ExampleName(config)#ctrl-Z

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.

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 routeand ipv6 route instructions.

ExampleName#config
ExampleName(config)#ip route 172.16.0.0 255.255.255.0 192.168.150.1
ExampleName(config)#ctrl-Z
ExampleName#show ip route
ExampleName#config
ExampleName(config)#ipv6 route fe80::230:1bff:fe80::/64 fe80::230:1bff:fe80::1
ExampleName(config)#ctrl-Z
ExampleName#show ipv6 route

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 like network congestion or network reliability.

There are many contrasting routing protocols, and they all use contrasting 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."

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.

Saving your Cisco Router config

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

If you switched the router off right now, and switched it on again, you would have to start configuration over again. Your running configuration is not saved to any perminent storage media. You'll 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 cisco router to that configuration, issue the command copy startup-config running-config.

ExampleName#copy startup-config running-config

    Example Cisco Router configuration
  1. Router>enable
  2. Router#config
  3. Router(config)#hostname C116-7206
  4. C116-7206(config)#interface serial 1/1
  5. C116-7206(config-if)ip address 192.168.145.2 255.255.255.0
  6. C116-7206(config-if)ipv6 address fe80::230:1bcf:fe80:b8ea/64
  7. C116-7206(config-if)ipv6 enable
  8. C116-7206(config-if)no shutdown
  9. C116-7206(config-if)ctrl-z
  10. C116-7206#show interface serial 1/1
  11. C116-7206#config
  12. C116-7206(config)#interface ethernet 2/3
  13. C116-7206(config-if)#ip address 192.168.140.90 255.255.255.0
  14. C116-7206(config-if)#no shutdown
  15. C116-7206(config-if)#ctrl-z
  16. C116-7206#show interface ethernet 2/3
  17. C116-7206#config
  18. C116-7206(config)#ip name-server 172.16.0.10
  19. C116-7206(config)#ctrl-z
  20. C116-7206#ping networkliquidationglobal.com
  21. C116-7206#config
  22. C116-7206(config)#enable secret passwd
  23. C116-7206(config)#ctrl-z
  24. C116-7206#copy running-config startup-config
  25. C116-7206#exit

You should now have a fully configured Cisco router. If you have any issues or concerns you should be able to consult the appropriate documentation, but this should get you started.

Router-to-router, configuration instructions may vary. Here are some basic steps which can be performed by your Cisco IT professionals. It may be helpful to also check out the corresponding documentation that may or may not have come with your cisco router. We provide some PDF's on the matter

If you need help with your router configuration try contacting your vendor for help.