Senior Acquisitions Editor: Kenyon Brown Development Editor: Kim Wimpsett
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- Bu səhifədəki naviqasiya:
- Doing the do Command
- Router and Switch Interfaces
- Bringing Up an Interface
- Serial Interface Commands
- Viewing, Saving, and Erasing Configurations
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Descriptions Setting descriptions on an interface is another administratively helpful thing, and like the hostname, it’s also only locally significant. One case where the description command comes in really handy is when you want to keep track of circuit numbers on a switch or a router’s serial WAN port. Here’s an example on my switch: Todd#
Todd(config)# int fa0/1 Todd(config-if)# description Sales VLAN Trunk Link Todd(config-if)# ^Z Todd#
And on a router serial WAN: Router#
config t Router(config)# int s0/0/0 Router(config-if)# description WAN to Miami Router(config-if)# ^Z You can view an interface’s description with either the show running- config
command or the show interface —even with the show interface description command:
Todd#sh run Building configuration... Current configuration : 855 bytes ! interface FastEthernet0/1 description Sales VLAN Trunk Link ! [output cut] Todd# sh int f0/1 FastEthernet0/1 is up, line protocol is up (connected) Hardware is Fast Ethernet, address is ecc8.8202.8282 (bia ecc8.8202.8282) Description: Sales VLAN Trunk Link MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec, [output cut] Todd#
sh int description Interface Status Protocol Description Vl1 up up Fa0/1 up up Sales VLAN Trunk Link Fa0/2 up up description: A Helpful Command Bob, a senior network admin at Acme Corporation in San Francisco, has over 50 WAN links to branches throughout the United States and Canada. Whenever an interface goes down, Bob wastes lots of time trying to figure out the circuit number and the phone number of the provider of his ailing WAN link. This kind of scenario shows just how helpful the interface description command can be. It would save Bob a lot of work because he could use it on his most important switch LAN links to find out exactly where every interface is connected. Bob’s life would also be made a lot easier by adding circuit numbers to each and every WAN interface on his routers, along with the phone number of the responsible provider. So if Bob had just taken time in advance to preventively add this information to his interfaces, he would have saved himself an ocean of stress and a ton of precious time when his WAN links inevitably go down!
Doing the do Command In every previous example so far, we’ve had to run all show commands from
privileged mode. But I’ve got great news—beginning with IOS version 12.3, Cisco has finally added a command to the IOS that allows you to view the configuration and statistics from within configuration mode! In fact, with any IOS, you’d get the following error if you tried to view the configuration from global config: Todd(config)# sh run ^ % Invalid input detected at '^' marker. Compare that to the output I get from entering that same command on my router that’s running the 15.0 IOS using the “do” syntax: Todd(config)#
Building configuration... Current configuration : 759 bytes ! version 15.0 no service pad service timestamps debug datetime msec service timestamps log datetime msec
no service password-encryption ! hostname Todd ! boot-start-marker boot-end-marker ! [output cut] So now you can pretty much run any command from any configuration prompt—nice, huh? Looking back through all those examples for encrypting our passwords, you can see that the do command would definitely have gotten the party started sooner, making this innovation one to celebrate for sure! Router and Switch Interfaces Interface configuration is arguably the most important router configuration because without interfaces, a router is a pretty useless object. Furthermore, interface configurations must be totally precise to enable communication with other devices. Network layer addresses, media type, bandwidth, and other administrator commands are all used to configure an interface. On a layer 2 switch, interface configurations typically involve a lot less work than router interface configuration. Check out the output from the powerful verification command show ip interface brief , which reveals all the interfaces on my 3560 switch: Todd#
sh ip interface brief Interface IP-Address OK? Method Status Protocol Vlan1 192.168.255.8 YES DHCP up up FastEthernet0/1 unassigned YES unset up up FastEthernet0/2 unassigned YES unset up up FastEthernet0/3 unassigned YES unset down down FastEthernet0/4 unassigned YES unset down down FastEthernet0/5 unassigned YES unset up up FastEthernet0/6 unassigned YES unset up up FastEthernet0/7 unassigned YES unset down down FastEthernet0/8 unassigned YES unset down down GigabitEthernet0/1 unassigned YES unset down down The previous output shows the default routed port found on all Cisco switches (VLAN 1), plus nine switch FastEthernet interface ports, with one port being a Gigabit Ethernet port used for uplinks to other switches. Different routers use different methods to choose the interfaces used on them. For instance, the following command shows one of my 2800 ISR Cisco routers with two FastEthernet interfaces along with two serial WAN interfaces: Router>
Interface IP-Address OK? Method Status Protocol FastEthernet0/0 192.168.255.11 YES DHCP up up FastEthernet0/1 unassigned YES unset administratively down down Serial0/0/0 unassigned YES unset administratively down down Serial0/1/0 unassigned YES unset administratively down down Router>
Previously, we always used the interface type number sequence to configure an interface, but the newer routers come with an actual physical slot and include a port number on the module plugged into it. So on a modular router, the configuration would be interface type slot/port , as demonstrated here: Todd#
Todd(config)# interface GigabitEthernet 0/1 Todd(config-if)# You can see that we are now at the Gigabit Ethernet slot 0, port 1 prompt, and from here we can make configuration changes to the interface. Make note of the fact that you can’t just type
. No
shortcuts on the slot/port—you’ve got to type the slot/port variables in the command: type slot/port or, for example, intgigabitethernet 0/1 (or just int g0/1 ).
Once in interface configuration mode, we can configure various options. Keep in mind that speed and duplex are the two factors to be concerned with for the LAN: Todd#
config t Todd(config)# interface GigabitEthernet 0/1 Todd(config-if)# speed 1000 Todd(config-if)# duplex full So what’s happened here? Well basically, this has shut off the auto-detect mechanism on the port, forcing it to only run gigabit speeds at full duplex. For the ISR series router, it’s basically the same, but you get even more options! The LAN interfaces are the same, but the rest of the modules are different—they use three numbers instead of two. The three numbers used here can represent slot/subslot/port , but this depends on the card used in the ISR router. For the objectives, you just need to remember this: The first 0 is the router itself. You then choose the slot and then the port. Here’s an example of a serial interface on my 2811: Todd(config)#
Todd(config)# interface serial 0/0/? <0-1> Serial interface number Todd(config)# interface serial 0/0/0 Todd(config-if)# This might look a little dicey to you, but I promise it’s really not that hard! It helps to remember that you should always view the output of the show ip interface brief command or a show running-config output first so you know the exact interfaces you have to deal with. Here’s one of my 2811’s output that has even more serial interfaces installed: Todd(config-if)#
Building configuration... [output cut] ! interface FastEthernet0/0 no ip address shutdown
duplex auto speed auto ! interface FastEthernet0/1 no ip address shutdown
duplex auto speed auto ! interface Serial0/0/0 no ip address shutdown
no fair-queue ! interface Serial0/0/1 no ip address shutdown
! interface Serial0/1/0 no ip address shutdown
! interface Serial0/2/0 no ip address shutdown
clock rate 2000000 ! [output cut] For the sake of brevity, I didn’t include my complete running-config, but I’ve displayed all you really need. You can see the two built-in FastEthernet interfaces, the two serial interfaces in slot 0 (0/0/0 and 0/0/1), the serial interface in slot 1 (0/1/0), and the serial interface in slot 2 (0/2/0). And once you see the interfaces like this, it makes it a lot easier to understand how the modules are inserted into the router. Just understand that if you type
on an old 2500 series router,
on a modular router (such as the 2800 series router), or
on an ISR router, all you’re actually doing is choosing an interface to configure. Essentially, they’re all configured the same way after that. Let’s delve deeper into our router interface discussion by exploring how to bring up the interface and set an IP address on it next. Bringing Up an Interface You can disable an interface with the interface command shutdown and
enable it with the no shutdown command. Just to remind you, all switch ports are enabled by default and all router ports are disabled by default, so we’re going to talk more about router ports than switch ports in the
next few sections. If an interface is shut down, it’ll display as administratively down when you use the show interfaces command ( sh int
for short): Router#
sh int f0/0 FastEthernet0/1 is administratively down, line protocol is down [output cut] Another way to check an interface’s status is via the show running-config command. You can bring up the router interface with the no shutdown command ( no shut for short): Router(config)# int f0/0 Router(config-if)# no shutdown *August 21 13:45:08.455: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up Router(config-if)# do show int f0/0 FastEthernet0/0 is up, line protocol is up [output cut]
Even though you don’t have to use IP on your routers, it’s usually what everyone uses. To configure IP addresses on an interface, use the ip address command from interface configuration mode and remember that you do not set an IP address on a layer 2 switch port! Todd(config)#
Todd(config-if)# ip address 172.16.10.2 255.255.255.0 Also, don’t forget to enable the interface with the no shutdown command.
Remember to look at the command show interface int output to see if the interface is administratively shut down or not. Show ip int brief and show running-config will also give you this information. The
ip address address mask command starts the IP processing on the router interface. Again, you do not configure an IP address on a layer 2 switch interface! Okay—now 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 primary IP address and mask.
This is definitely one of the Cisco IOS’s coolest features! So let’s try it. To add a secondary IP address, just use the secondary parameter: Todd(config-if)#
secondary Make this IP address a secondary address Todd(config-if)# ip address 172.16.20.2 255.255.255.0 secondary Todd(config-if)# do sh run Building configuration... [output cut] interface FastEthernet0/1 ip address 172.16.20.2 255.255.255.0 secondary ip address 172.16.10.2 255.255.255.0 duplex auto speed auto ! But I’ve got to stop here to tell you that I really wouldn’t recommend having multiple IP addresses on an interface because it’s really inefficient. I showed you how anyway just in case you someday find yourself dealing with an MIS manager who’s in love with really bad network design and makes you administer it! And who knows? Maybe someone will ask you about it someday and you’ll get to seem really smart because you know this. Using the Pipe No, not that pipe. I mean the output modifier. Although, I’ve got to say that some of the router configurations I’ve seen in my career make me wonder! Anyway, 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: Router#
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
Router# sh run | begin interface interface FastEthernet0/0 description Sales VLAN ip address 10.10.10.1 255.255.255.248 duplex auto speed auto ! interface FastEthernet0/1 ip address 172.16.20.2 255.255.255.0 secondary ip address 172.16.10.2 255.255.255.0 duplex auto speed auto ! interface Serial0/0/0 description Wan to SF circuit number 6fdda 12345678 no ip address ! So basically, the pipe symbol—the output modifier—is what you need to help you get where you want to go light years faster than mucking around in a router’s entire configuration. I use it a lot when scrutinizing a large routing table to find out whether a certain route is in the routing table. Here’s an example: Todd#
R 192.168.3.32 [120/2] via 10.10.10.8, 00:00:25, FastEthernet0/0 Todd#
First, you need to know that this routing table had over 100 entries, so without my trusty pipe, I’d probably still be looking through that output! It’s a powerfully efficient tool that saves you major time and effort by quickly finding a line in a configuration—or as the preceding example shows, a single route within a huge routing table. Give yourself a little time to play around with the pipe command to get the hang of it and you’ll be naturally high on your newfound ability to quickly parse through router output! Serial Interface Commands But wait! Before you just jump in and configure a serial interface, you need some key information, like knowing the interface will usually be attached to a CSU/DSU type of device that provides clocking for the line to the router. Check out Figure 6.3 for an example.
FIGURE 6.3 A typical WAN connection. Clocking is typically provided by a DCE network to routers. In nonproduction environments, a DCE network is not always present. 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, such as one that’s used in a lab environment like the one in Figure 6.4 , one end—the data communication equipment (DCE) end of the cable—must provide clocking! FIGURE 6.4 Providing clocking on a nonproduction network By default, Cisco router serial interfaces are all data terminal equipment (DTE) interfaces, which means that you must configure an interface to provide clocking if you need it to act like a DCE device. Again, you would not provide clocking on a production WAN serial connection because you would have a CSU/DSU connected to your serial interface, as shown in Figure 6.3 . You configure a DCE serial interface with the clock rate command:
Router# config t Enter configuration commands, one per line. End with CNTL/Z. Router(config)#
Router(config-if)# clock rate ? Speed (bits per second) 1200 2400
4800 9600
14400 19200
28800 32000
38400 48000
56000 57600
64000 72000
115200 125000
128000 148000
192000 250000
256000 384000
500000 512000
768000 800000
1000000 2000000
4000000 5300000
8000000 <300-8000000> Choose clockrate from list above Router(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
command:
Router# 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 depicting a DCE connection: Router#
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. Every Cisco router ships with a default serial link bandwidth of T1 (1.544 Mbps). But this has nothing to do with how data is transferred over a link. The bandwidth of a serial link is used by routing protocols such as EIGRP and OSPF to calculate the best cost path to a remote network. So if you’re using RIP routing, the bandwidth setting of a serial link is irrelevant since RIP uses only hop count to determine this. You may be rereading this part and thinking, “Huh? What? Routing protocols? Metrics?” But don’t freak! I’m going over all of that soon in Chapter 9. Here’s an example of using the bandwidth command:
Router# config t Router(config)# int s0/0/0 Router(config-if)# bandwidth ? <1-10000000> Bandwidth in kilobits inherit Specify that bandwidth is inherited receive Specify receive-side bandwidth Router(config-if)# bandwidth 1000 Did you notice that, unlike the clock rate command, the bandwidth
command is configured in kilobits per second? After going through all these configuration examples regarding the clock rate command, understand that the new ISR routers automatically detect DCE connections and set clock rate to 2000000. But know that you still need to understand the clock rate command for the Cisco objectives, even though the new routers set it for you automatically!
If you run through setup mode, you’ll be asked if you want to use the configuration you just created. If you say yes, the configuration running in DRAM that’s known as the running-config will be copied into NVRAM, and the file will be named startup-config . Hopefully, you’ll be smart and always use the CLI, not setup mode! You can manually save the file from DRAM, which is usually just called RAM, to NVRAM by using the copy running-config startup-config command. You can use the shortcut copy run start as well:
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