If you have just turned on the router, it will be completely unconfigured. If it is already configured, you may want to view its current configuration. Even if it has not been previously configured, you should familiarize yourself with the
show commands before beginning to configure the router. Enter privileged mode by issuing the command enable, then issue several show commands to see what they display. Remember, the command show ? will display all the showcommands aavailable in the current mode. Definately try out the following commands:
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 enter privileged mode by using the command enable, you are in the top-level mode of privileged mode, also known in this document as "parent mode." It is in this top-level or parent mode that you can display most of the information about the router. As you now know, you do this with the show commands. Here you can learn the configuration of interfaces and whether they are up or down. You can display what IP protocols are in use, such as dynamic routing protocols. You can view the route and ARP tables, and these are just a few of the more important options.
As you configure the router, you will enter various sub-modes to set options, then return to the parent mode to display the results of your commands. You also return to the parent mode to enter other sub-modes. To return to the parent mode, you hit ctrl-z. This puts any commands 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 first sub-mode of the parent mode. In the parent mode, you issue the command
config. Router#config
Router(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
ExampleName(config)# 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
ExampleName(config)#ctrl-Z
ExampleName# This is also where you set the password for privileged mode.
ExampleName(config)#enable secret examplepassword
ExampleName(config)#ctrl-Z
ExampleName# 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:
ExampleName# 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.
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
ExampleName(config)#interface serial 1/1
ExampleName(config-if)#ip address 192.168.155.2 255.255.255.0
ExampleName(config-if)#ipv6 address fe80::230:1bff:fe80:b8ea/64
ExampleName(config-if)#ipv6 enable
ExampleName(config-if)#no shutdown
ExampleName(config-if)#ctrl-Z
ExampleName# 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(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 192.168.155.2 255.255.255.0
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 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.
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
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 route and ipv6 route commands.
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 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."
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.
IPv6 configuration with IOS
This is a seperate section because IPv6 is new to most people, and they will be looking specifically for information about configuring IPv6. Examples of configuring IPv6 are included throughout the document, however, alongside IPv4. That is a more accurate reflection of how you will work with IPv6 on a day-to-day basis. Once the newness of IPv6 passes, it will be one more piece in the familiar puzzle.
The important concept to understand when configuring IPv6 is that IPv4 and IPv6 exist in parrallel. One is not a replacement for the other, at least not in the way it is treated by the operating system. A term for this is dual stack. An interface can have an IPv4 address and no IPv6 address. Or an IPv6 address and no IPv4 address. Or both an IPv4 address and an IPv6 address. Examples:
IPv4 only
!
interface FastEthernet0/0
ip address 192.168.1.138 255.255.255.0
!
IPv6 only
!
interface FastEthernet0/0
ipv6 address fe80::230:1bff:fe80::/64
ipv6 enable
!
IPv4 and IPv6
!
interface FastEthernet0/0
ip address 192.168.1.138 255.255.255.0
ipv6 address fe80::230:1bff:fe80::/64
ipv6 enable
!
Notice that there are seperate but similiar commands for IPv4 and IPv6. To assign an IPv4 address,
ExampleName(config-if)#ip address 192.168.1.138 255.255.255.0
To assign an IPv6 address,
ExampleName(config-if)#ipv6 address fe80::230:1bff:fe80::/64
There are some bigger differences between IPv4 and IPv6 IOS commands. For example, the IPv6 equivilant of show ip arp, is show ipv6 neighbors.
3.5 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
Example Cisco Router configuration
- Router>enable
- Router#config
- Router(config)#hostname N115-7206
- N115-7206(config)#interface serial 1/1
- N115-7206(config-if)ip address 192.168.155.2 255.255.255.0
- N115-7206(config-if)ipv6 address fe80::230:1bff:fe80:b8ea/64
- N115-7206(config-if)ipv6 enable
- N115-7206(config-if)no shutdown
- N115-7206(config-if)ctrl-z
- N115-7206#show interface serial 1/1
- N115-7206#config
- N115-7206(config)#interface ethernet 2/3
- N115-7206(config-if)#ip address 192.168.150.90 255.255.255.0
- N115-7206(config-if)#no shutdown
- N115-7206(config-if)#ctrl-z
- N115-7206#show interface ethernet 2/3
- N115-7206#config
- N115-7206(config)#ip name-server 172.16.0.10
- N115-7206(config)#ctrl-z
- N115-7206#ping archie.au
- N115-7206#config
- N115-7206(config)#enable secret password
- N115-7206(config)#ctrl-z
- N115-7206#copy running-config startup-config
- N115-7206#exit
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