This chapter describes how to access a router through the following methods:
- Through a direct console connection
- Over the LAN via Telnet
- Through a terminal server
In this chapter, you learn how to access a router and switch through a direct console connection, over the LAN via Telnet, and finally through a terminal server. To begin, this chapter reviews how to access a router or switch through a direct console connection. Next, you will configure the terminal server router for Telnet access. Then you will access the terminal server over the LAN via Telnet using a terminal application program running on your PC. Finally, you will configure the 2511 router as the lab terminal server for reverse Telnet to access the lab routers.
Routers and switches can be accessed and configured through various means. To initially configure a Cisco device, you will need to connect directly through the console port. The console port exists on both routers and switches and is available to configure and monitor the device.
Direct Access to Routers and Switches Through a Console Port
Most Cisco devices use a rollover cable connected to the console port on the router or switch. For exceptions, consult the product documentation to verify whether you should use a straight-through or rollover cable. The cable is then connected to an RJ-45toDB-9 or RJ-45toDB-25 terminal adapter that is attached to a serial communications port (COM1, COM2, or other COM port) on the PC. Figure 4-1 shows how this is done.
When the physical connection is in place, configure the terminal application program on the PC with the following COM settings:
- 9600 bps
- 8 data bits
- No parity
- 1 stop bit
- No flow control
In the lab, you will be using the terminal application program HyperTerminal to connect to the terminal server's console port. Any terminal application could be used based on your personal preference. If another terminal application is used, consult the product documentation for configuration and setup procedures.
The version of HyperTerminal has changed over the years to address functionality problems within the application. For example, older versions that came with Windows 95 and NT could not send the Ctrl-Break sequence (needed to break into the router). An early version that came with NT Service Pack 2 or 3 fixed this issue but had a problem when pasting several commands into the configuration scriptit took about 5 seconds per line while it sent CPU utilization to 100 percent. The version that comes with NT-SP5, 98, and 2000 is fine. The authors of the program (Hilgraeve) provide a free update. To obtain the free update, open HyperTerminal, click Help, About, Upgrade Information, and then follow the upgrade instructions, or visit http://www.hilgraeve.com.
Accessing the Lab Terminal Server Through the Console Port
The physical cabling between your PC and the router acting as the terminal server has been configured as shown in Figure 4-1. With the physical cabling in place, start the program HyperTerminal on the PC. To do so, click Start, Programs, Accessories, Communications, HyperTerminal. Then double-click the HyperTerminal executable (hypertrm.exe) from within Windows, as shown in Figure 4-2.
Figure 4-2 Starting the HyperTerminal Application
Give the new connection a name of LAB, and then click OK, as shown in Figure 4-3.
Figure 4-3 Giving the Connection a Name
In the Connect Using field, select Direct to Com1 from the drop-down menu, as shown in Figure 4-4.
This step is correct for the newest versions of HypterTerminal. For older versions of HyperTerminal, it is done differently. Hilgraeve provides a free update to HyperTerminal when used for personal use. Visit http://www.hilgraeve.com and download HyperTerminal Private Edition.
Figure 4-4 Selecting the COM Port on PC
Now configure the port settings as follows and as shown in Figure 4-5. When finished, click OK:
- Bits per second: 9600
- Data bits: 8
- Parity: none
- Stop bits: 1
- Flow control: none
Figure 4-5 Configuring HyperTerminal Port Settings
You are initially placed in user EXEC mode of the terminal server. If you do not see a prompt, hit the Enter key a few times, and then type enable and hit Enter. You are put into privileged EXEC mode without being prompted for a password because an enable password has not yet been set, as shown in Figure 4-6.
Figure 4-6 Successful Establishment of EXEC Session Through a Direct Console Connection
If you still do not get a console prompt, verify that it shows Connected in the bottom-left corner of the HyperTerminal application, as shown in Figure 4-6. If not, check the physical cabling as well as the port settings, and verify that the router has been powered on.
Now that you have successfully connected to the console port of the terminal server, you will configure the terminal server for Telnet access.
Configuring the Terminal Server for Telnet Access
In this section, you will configure the terminal server so that you can Telnet to it across the network. When you are connected to the terminal server, the terminal server will be the single point from which you may access all other lab routers through reverse Telnet. A terminal server provides out-of-band access to several devices. Out-of-band access is through a router's console or aux port versus in-band access that occurs over a network through Telnet or SNMP. Telnet, reverse Telnet, and a terminal server overview are covered in greater detail later in the chapter.
The next step is to make the terminal server accessible over your Ethernet network so that you can access it from any workstation on the LAN, as shown in Figure 4-7.
Figure 4-7 LAN Configuration for Telnet Access
Telnet access is useful because it eliminates the requirement to be physically at the terminal server router to gain access. Instead, you can configure the terminal server so that you can Telnet to it over the LAN, as shown in Figure 4-7. Then, from the terminal server, you will be able to access each lab router through reverse Telnet, as shown in Figure 4-8. Reverse Telnet will be explained and demonstrated later in this chapter.
Figure 4-8 Terminal Server Logical Diagram
Begin by configuring the terminal servers' host name, Ethernet IP address, and vty lines. Because you're still attached via a direct connection to the terminal server's console port, ensure you're in privileged EXEC mode by typing enable from user EXEC mode, as in Example 4-1.
Example 4-1 Entering Enable Mode on Terminal Server
Because the privileged EXEC password has not yet been set, you are allowed directly into privileged EXEC mode without entering a password, as denoted by the Router# prompt in Example 4-1. To change the host name on the router, type configure terminal to enter global configuration mode. Next, issue the hostname command followed by Termserver, as shown in Example 4-2.
Example 4-2 Changing the Host Name on the Terminal Server
Router>enable Router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)#hostname Termserver Termserver(config)#
Notice that the prompt has changed from Router(config)# to Termserver(config)#.
Next, from global configuration mode, enter interface configuration mode by typing interface ethernet0, and assign the IP address of 10.160.8.1 with a mask of 255.255.255.0 to the Ethernet0 interface. In addition, ensure that the interface is not shut down by typing no shutdown from interface configuration mode for Ethernet 0, as demonstrated in Example 4-3.
Example 4-3 Assign the Terminal Server's Ethernet 0 Interface an IP Address and Bring the Interface Out of Shutdown Mode
Router>enable Router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)#hostname Termserver Termserver(config)# Termserver(config)#interface ethernet0 Termserver(config-if)#ip address 10.160.8.1 255.255.255.0 Termserver(config-if)#no shutdown Termserver(config-if)# %LINEPROTO-5-UPDOWN: Line protocol on Interface Ethernet0, changed state to up Termserver(config-if)# %LINK-3-UPDOWN: Interface Ethernet0, changed state to up Termserver(config-if)#
Notice that you receive a console message indicating that the line protocol on Ethernet 0 is up and the interface is up. You can verify that Ethernet 0 is up and configured with the proper IP address by typing show interface ethernet0, as shown in Example 4-4.
Example 4-4 Verifying that Ethernet 0 Is Up and Configured with the Correct IP Address
Termserver#show interface ethernet0 Ethernet0 is up, line protocol is up Hardware is Lance, address is 0000.0c47.351c (bia 0000.0c47.351c) Internet address is 10.160.8.1/24 MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, rely 255/255, load 1/255 Encapsulation ARPA, loopback not set, keepalive set (10 sec) ARP type: ARPA, ARP Timeout 04:00:00 Last input 00:00:00, output 00:00:00, output hang never Last clearing of "show interface" counters never Queueing strategy: fifo Output queue 0/40, 0 drops; input queue 1/75, 0 drops 5 minute input rate 0 bits/sec, 1 packets/sec 5 minute output rate 0 bits/sec, 1 packets/sec 6674 packets input, 1267069 bytes, 0 no buffer Received 6252 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 0 input packets with dribble condition detected 12718 packets output, 1199744 bytes, 0 underruns 0 output errors, 0 collisions, 0 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out
You can see that Ethernet 0 is up as shown in the highlighted lines of Example 4-4 because the interface is up and the line protocol is up. In addition, you see that the IP address of 10.160.8.1 and mask of 255.255.255.0 (/24) are configured on the interface.
The workstation has been assigned an IP address of 10.160.8.65 with a subnet mask of 255.255.255.0. From the workstation, verify that you can ping the newly assigned IP address on your terminal server's Ethernet 0 interface, as shown in Figure 4-9.
Figure 4-9 Verify IP Connectivity Between Workstation and Terminal Server
vty Line Configuration for Telnet Access
Virtual terminal lines are used to allow remote access to a router. A virtual terminal line is not associated with either the auxiliary or console port; instead, it is a "virtual port" on the router. The router has five virtual terminal lines, by default. You will configure the five vty lines (vty 0 through 4) for Telnet access and set a password of falcons on these lines. In addition, you want to ensure that, after 15 minutes of inactivity on the vty lines, the connection times out. To configure the vty lines, you will do the following from global configuration mode:
|Step 1||Enter line configuration mode.|
|Step 2||Enable login on the vty lines.|
|Step 3||Set a password for Telnet access.|
|Step 4||Set the exec-timeout interval.|
To examine how this is done, first enter line configuration mode for vty lines 0 through 4, as shown in Example 4-5.
Example 4-5 Line Configuration Mode for vty 0 Through 4
Termserver#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Termserver(config)#line vty 0 4 Termserver(config-line)#
You can verify that you have successfully entered line configuration mode because the prompt has changed, as shown in the highlighted portion of Example 4-5. Next, enable login on the vty lines and set a Telnet password of falcons on the terminal server, as in Example 4-6.
Example 4-6 Configure vty Lines with Login and Password Checking
Termserver(config-line)#login Termserver(config-line)#password falcons
Remember that if an enable password has not been set on the router, you cannot Telnet into the router. This is true even when a password has been set on the vty lines. Although not shown here, assume that the terminal server has been configured with the enable password falcons.
Finally, it is a good idea to set timeout values on your vty lines so that idle Telnet sessions will not remain up indefinitely. By default, the exec-timeout is set to 10 minutes on both the console and the vty ports.
The timeout value is specified in minutes and seconds. You will set the timeout value to 15 minutes and 0 seconds on vty lines 0 through 4 using the exec-timeout command. If you are unsure of the order in which to specify minutes and seconds, use context-sensitive help, as shown in Example 4-7.
Example 4-7 Setting the exec-timeout Value to 15 Minutes and 0 Seconds on vty Lines 0 Through 4
Termserver(config-line)#exec-timeout ? <0-35791> Timeout in minutes Termserver(config-line)#exec-timeout 15 ? <0-2147483> Timeout in seconds <cr> Termserver(config-line)#exec-timeout 15 0 Termserver(config-line)#
Verify the configuration changes in your running-config by exiting back to privileged EXEC with CTRL-Z and then using a show running-config command. The highlighted section of Example 4-8 shows the last portion of the running-config with the configuration of the five vty lines.
Example 4-8 Verify Changes with show running-config Command
Termserver(config-line)#^Z Termserver#show running-config line con 0 login line 1 16 line aux 0 line vty 0 4 exec-timeout 15 0 password 7 15140A0007252537 login
The end of the config shows all lines on the router, as well as the changes you have made to the vty lines.
Saving the Running Configuration
Save the configuration by typing copy running-config startup-config from global configuration mode, as shown in Example 4-9.
Example 4-9 Copy running-config to startup-config
Termserver#copy running-config startup-config Building configuration... [OK] Termserver#
If you are running Cisco IOS software Release 12.0 or later, the copy command may ask for a confirmation in this form: Destination file [startup-config]?.
The configuration has been successfully copied from the running configuration to the startup configuration, as denoted by the [OK] highlighted in Example 4-9.
Accessing the Terminal Server from a PC over a LAN/WAN via Telnet
Now you will test to see if you can Telnet to the terminal server at 10.160.8.1. To do so, configure the terminal application program (HyperTerminal) to Telnet to the router. This is done by starting HyperTerminal and, instead of selecting a COM port to connect through, selecting TCP/IP (Winsock), as shown in Figure 4-10.
If the TCP/IP option is not available, you have an older version of the HypterTerminal Application. You can upgrade it at http://www.hilgraeve.com.
Figure 4-10 HyperTerminal Configured to Use TCP/IP
Next, enter the IP address of 10.160.8.1, as shown in Figure 4-11.
Figure 4-11 Telnet to Ethernet 0 10.160.8.1
You are first prompted for the Telnet password of falcons that you configured previously in Example 4-6. When this password is successfully supplied, you are taken into user EXEC mode. From there, you can type enable to gain access to privileged EXEC mode.
You have now successfully Telnetted to the terminal server.
Configuring the Terminal Server
This section demonstrates how to configure a terminal server to provide access to the rest of the routers in the lab. Once configured, you will be able access each lab router's console port through reverse Telnet.
In this chapter, you will accomplish the following lab objective:
Configure the Cisco 2511 router to be the terminal server for this lab. The terminal server is connected to each device's console port. Port assignments are as follows:
- Catalyst Switch2007
After completing this objective, you will learn how to maneuver from the terminal server to each individual lab router and then back to the terminal server.
Terminal Server Overview
A terminal server provides out-of-band access for several devices. Out-of-band access is through a router's console or aux port versus in-band access that occurs over the network using telnet. Generally, a terminal server is a router with multiple, asynchronous ports that are connected to other devices, such as the console port of other routers or switches, as shown previously in Figure 4-8. To get a better idea of what the ports look like on the back of a terminal server, see Figure 4-12, which shows the back of a Cisco 2511.
Figure 4-12 A Cisco 2511 to Be Configured as the Lab Terminal Server
The Cisco 2511 series router uses a 68-pin connector and breakout cable (see Figure 4-13).
Figure 4-13 CAB-OCTAL-ASYNC Cable
This cable is referred to as a CAB-OCTAL-ASYNC cable or just OCTAL cable. It provides eight RJ-45 rolled cable asynchronous (async) ports on each 68-pin connector. The 68-pin connector is attached to Interface Async 1 of the terminal server. Each RJ-45 rolled cable is connected to the console port of each router in the lab. For configuration purposes, each rolled cable is referred to as an asynchronous line in the configuration. Each line is numbered beginning with 2001 to 2008. So, R1 is attached to async 2001, R2 is connected to 2002, and so on up to 2007, which is connected to the Catalyst 1900 switch, leaving 2008 unused. See Figure 4-14 for an example.
Figure 4-14 Terminal Server Connectivity to Lab Routers
The async ports from the 68-pin connector are data terminal equipment (DTE) devices. DTE-to-DTE connections require a rolled (null modem) cable. DTE-to-DCE devices require a straight-through cable. Because the Octal cable is rolled, you can connect each cable directly to the RJ-45 console port of each lab router. However, some routers have console ports that are 25-pin interfaces instead of RJ-45. If so, remember that the 25-pin interface is a DCE, and you must use the RJ-45-to-25 pin adapter marked "modem" to reverse the roll and complete the connection.
The major benefit of a terminal server is that it allows you a single point from which to access the console ports of many devices. This is helpful initially in the lab because the lab routers will not have any configuration settings such as IP addresses or Telnet parameters. Without the terminal server, you would have the tedious process of manually switching between each router's console port to gain access. A second benefit is that a terminal server can provide fault tolerance in case the routers become inaccessible because of a network failure. This is because you can configure a modem on the auxiliary or asynchronous port of the terminal server, allowing dialup connectivity to the terminal server and thus to each router that the terminal server is connected to.
In the lab, the terminal server will be the single point from which you may access all other lab routers through reverse telnet.
Most Telnet connections are considered forward connections, or connections accepted into a line or interface. Reverse Telnet means that the Telnet session is initiated out of the line (like an asynchronous line) instead of accepting a connection into the line. Thus, reverse Telnet allows you to Telnet out from a device that you are Telnetting to, but on a different interface, such as an asynchronous port. For example, the terminal server has a LAN (Ethernet) IP address of 10.160.8.1. If you want to connect to R1 on asynchronous line 2001, you would issue the following command from the terminal server:
Termserver#telnet 10.160.8.1 2001
Essentially, you are telling the router to connect to its own Ethernet 0 IP address of 10.160.8.1 via Telnet but to initiate the connection out line 2001. This will be a fundamental part of the lab exercises, so let's demonstrate how this is done.
In the lab, you will do reverse Telnet using an IP address assigned to a loopback interface. Loopback addresses are preferred because they are virtual and thus always available. For reverse Telnet to work, the interface that is used must be up and the line protocol must be up. Because of this, using a loopback interface is advantageous because it never goes down, as opposed to an Ethernet interface, which might go down and prevent reverse Telnet from working.
Terminal Server Configuration
Now that you have an understanding of how the terminal server is physically connected and how reverse Telnet functions, it's time to examine how to configure the terminal server.
The steps to configure the terminal server are as follows:
|Step 1||Create a loopback interface.|
|Step 2||Assign an IP address to the loopback interface.|
|Step 3||Allow Telnet as a transport across asynchronous lines 1 to 16.|
|Step 4||Create a host table that maps a router's host name (such as R1, R2, and so on) to the asynchronous line it is connected to on the terminal server (such as 2001, 2002, and so on).|
Steps 1 and 2: Creating a Loopback Interface and Assigning an IP Address
Begin by creating the loopback interface from global configuration mode. Going into interface configuration mode for the loopback 0 interface creates the loopback interface and brings up the interface, as highlighted in Example 4-11. You can assign the interface any number in the range of 0 to 2147483647. Use loopback 0 and assign it an IP address of 192.168.10.10 with a mask of 255.255.255.0, as shown in Example 4-10.
Example 4-10 Creating loopback 0 and Assigning It an IP Address
Termserver(config)# Termserver(config)#interface loopback0 Termserver(config-if)# %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback0, changed state to up Termserver(config-if)# %LINK-3-UPDOWN: Interface Loopback0, changed state to up Termserver(config-if)#ip address 192.168.10.10 255.255.255.0
Exit interface configuration mode by doing a CTRL-Z and do a show running-config to show how this interface now appears in the output in Example 4-11.
Example 4-11 loopback0 Interface as It Appears in Running-Config After Creation
Termserver(config-if)#^Z Termserver#show running-config Current configuration: ! version 11.2 service password-encryption no service udp-small-servers no service tcp-small-servers ! hostname Termserver ! enable password 7 0200055708090132 ! interface Loopback0 ip address 192.168.10.10 255.255.255.0 !
You can also do a show interface loopback0 to verify that the loopback interface is up and has the correct IP address, as in Example 4-12.
Example 4-12 show interface loopback0 Command Output Verifies Interface Status and IP Address
Termserver#show interface loopback0 Loopback0 is up, line protocol is up Hardware is Loopback Internet address is 192.168.10.10/24 MTU 1514 bytes, BW 8000000 Kbit, DLY 5000 usec, rely 255/255, load 1/255 Encapsulation LOOPBACK, loopback not set, keepalive set (10 sec) Last input never, output never, output hang never Last clearing of "show interface" counters never Queueing strategy: fifo Output queue 0/0, 0 drops; input queue 0/75, 0 drops 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 0 packets input, 0 bytes, 0 no buffer Received 0 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 0 packets output, 0 bytes, 0 underruns 0 output errors, 0 collisions, 0 interface resets 0 output buffer failures, 0 output buffers swapped out Termserver#
Step 3: Allowing Telnet as a Transport Across Asynchronous Lines 1 to 16
Now that the loopback 0 interface is created, you need to ensure that the asynchronous lines allow Telnet to traverse the lines.
This is done using the transport input x command, where x is the protocol that you want to allow, such as Telnet. The command allows the granularity of permitting only certain protocols to cross the asynchronous lines. The allowed protocols are shown using context-sensitive help, as demonstrated in Example 4-13.
Example 4-13 Available Protocols Configurable for Transport Across the Asynchronous Lines
Termserver(config)#line 1 16 Termserver(config-line)#transport input ? all All protocols lat DEC LAT protocol mop DEC MOP Remote Console Protocol nasi NASI protocol none No protocols pad X.3 PAD rlogin Unix rlogin protocol telnet TCP/IP Telnet protocol v120 Async over ISDN Termserver(config-line)#transport input
In the lab, you will do a transport input telnet to allow Telnet to cross the lines.
Enter line configuration mode for asynchronous lines 1 through 16. To do this, type line 1 16 from privileged EXEC mode.
In the lab, you are really concerned with only Lines 1 to 7 (2001 to 2007) because they are the only asynchronous lines that have routers connected to them. However, because a Cisco 2511 has two asynchronous interfaces, 16 lines total are available (8 per asynchronous interface) for configuration.
Upon entering line configuration mode, allow all protocols to be transported across the lines, as shown in Example 4-15.
Example 4-14 Allow All Protocols to Cross the Asynchronous Lines
Termserver(config)#line 1 16 Termserver(config-line)#transport input telnet Termserver(config-line)#^Z
Step 4: Creating a Host Table That Maps a Router's Host Name to the Asynchronous Line to Which It Is Connected on the Terminal Server
At this point, the terminal server is configured and should be functional; however, as a timesaver, you will create a host table that maps the router name to the loopback 0 interface and then specify the asynchronous port out which to initiate the reverse Telnet session. This is done using the ip host command. The ip host command is a static DNS entry used by the router. The router will translate "R1" to 192.168.10.10 port 2001. When this host table is completed, you will access each router by typing the host name of the router. For example, typing R1 initiates a reverse Telnet session out asynchronous line 1 (2001). Create the table from global configuration mode as shown in Example 4-15.
Example 4-15 Creating IP Host Table for Reverse Telnet
Termserver#config t Enter configuration commands, one per line. End with CNTL/Z. Termserver(config)#ip host r1 2001 192.168.10.10 Termserver(config)#ip host r2 2002 192.168.10.10 Termserver(config)#ip host r3 2003 192.168.10.10 Termserver(config)#ip host r4 2004 192.168.10.10 Termserver(config)#ip host r5 2005 192.168.10.10 Termserver(config)#ip host r6 2006 192.168.10.10 Termserver(config)#ip host cat19 2007 192.168.10.10 Termserver(config)#
Saving and Testing the Terminal Server Configuration
Exit back to global configuration mode by doing a CTRL-Z and then save the configuration. Next, test reverse Telnet functionality by typing r1 from user EXEC or privileged EXEC mode, as shown in Example 4-16.
Example 4-16 Successful Reverse Telnet to R1
Termserver#^Z Termserver#copy running startup Building configuration... [OK] Termserver#r1 Trying r1 (192.168.10.10, 2001)... Open Hit enter key Router>
You can see from Example 4-16 that the terminal server initiates a connection to R1. It does this by connecting to its own loopback 0 address of 192.168.10.10 (via Telnet) and then redirecting the connection out asynchronous port 2001. Because the Telnet connection is "redirected," it is referred to a reverse Telnet connection. Next, hit the Enter key to get the Router> prompt. R1's console port is connected to asynchronous line 1 (port 2001) of the terminal server. By hitting the Enter key, you are placed into R1's user EXEC mode. At this point, give the router a host name of R1 to avoid confusion about which router you are connected to. Change the host name to R1, and save the changes, as shown in Example 4-17.
Example 4-17 Hostname Changed from Router to R1
Router>enable Router#conf t Enter configuration commands, one per line. End with CNTL/Z. Router(config)#hostname R1 R1(config)#^Z R1#copy running startup Building configuration... [OK] R1#
To get back to the terminal server, type Ctrl-Shift-6, x from R1, as in Example 4-18.
Example 4-18 Return to the Terminal Server via the Escape Sequence
R1#Ctrl-Shift-6, x Termserver#
Upon doing the escape sequence (Ctrl-Shift-6, x), notice that you have been returned to the terminal server, as shown by the change from the R1# prompt to the Termserver# prompt in Example 4-18.
Connecting, Disconnecting, and Verifying Reverse Telnet Sessions
From the terminal server, you can view active reverse Telnet connections by doing show sessions, as in Example 4-19.
Example 4-19 Established Sessions on the Terminal Server
Termserver#show sessions Conn Host Address Byte Idle Conn Name * 1 r1 192.168.10.10 0 3 R1 Termserver#
When a reverse Telnet session is established, the session is given a connection number. The asterisk preceding the connection number indicates that the session is active, as highlighted in Example 4-19.
To return to an active session, you can simply enter the connection number. Upon seeing the message [Resuming connection 1 to R1 ... ], press the Enter key and you are taken to R1, as demonstrated in Example 4-20.
Example 4-20 Resuming an Active Reverse Telnet Session Using the Connection Number
Termserver#1 [Resuming connection 1 to r1 ... ] Hit Enter key R1#
Occasionally, when initiating the reverse Telnet session, the connection might be refused and you will not be able to get into a router; you will see a message as shown in Example 4-21.
Example 4-21 Reverse Telnet Session Refused by Remote Host
Termserver#r1 Trying r1 (192.168.10.10, 2001)... % Connection refused by remote host Termserver#
When the connection is refused, you need to clear the asynchronous line and attempt the reverse Telnet again. This is done by doing a clear line 1, confirming the request by pressing Enter, and then entering r1 to reinitiate the reverse Telnet connection, as shown in Example 4-22.
Example 4-22 Clearing the Asynchronous Line 1 After a Connection Is Refused and Reinitiating the Reverse Telnet Connection
Termserver#r1 Trying r1 (192.168.10.10, 2001)... % Connection refused by remote host Termserver#clear line 1 [confirm] [OK] Termserver#r1 Trying r1 (192.168.10.10, 2001)... Open R1>
You might need to clear the line a few times before it completely clears.
You have now successfully connected to R1 through reverse Telnet.
Return to the terminal server from R1 using Ctrl-Shift-6, x. Execute a show sessions command on the terminal server to display that connection 1 is an established reverse Telnet session to R1. To disconnect a previously established reverse Telnet session, you can enter disconnect and the connection number, and then hit Enter to confirm the disconnect, as shown in Example 4-23.
Example 4-23 Disconnecting an Established Reverse Telnet Session
R1> Termserver#show sessions Conn Host Address Byte Idle Conn Name * 1 r1 192.168.10.10 0 0 R1 Termserver#disconnect 1 Closing connection to r1 [confirm] Termserver#
Now if you do a show sessions on the terminal server, as demonstrated in Example 4-24, you can see that the reverse Telnet session to R1 was disconnected.
Example 4-24 No Active Reverse Telnet Session After Doing a Disconnect
Termserver#show sessions % No connections open Termserver#
To finish, set up a reverse Telnet connection to each of the lab devices, R1 through R6. First, you'll connect to each router by typing the router's host name, hitting Enter, and then entering the escape sequence Ctrl-Shift-6, x to get back to the terminal server to repeat the process for the next router (see Example 4-25).
Example 4-25 Setting Up a Reverse Telnet Session to Each Lab Router
Termserver#r1 Trying r1 (192.168.10.10, 2001)... Open R1> Termserver#r2 Trying r2 (192.168.10.10, 2002)... Open Router> Termserver#r3 Trying r3 (192.168.10.10, 2003)... Open Router> Termserver#r4 Trying r4 (192.168.10.10, 2004)... Open Router> Termserver#r5 Trying r5 (192.168.10.10, 2005)... Open Router> Termserver#r6 Trying r6 (192.168.10.10, 2006)... Open Router> Termserver#
Notice in Example 4-25 that the reverse Telnet session is successful because the connection shows Open and you are taken to the router prompt of each respective device. R1 is the only router with a configured host name because it is the only router that you have configured with a host name so far. Thus, the remaining routers take you to the Router> prompt.
Individual host names for the remaining routers will be configured in Chapter 6, "General Router Configurations."
Reverse Telnetting to the Catalyst 1900 Switch
Next, establish a reverse Telnet session to the Catalyst 1900 switch by entering cat1900 and pressing Enter, as shown in Example 4-26.
Example 4-26 Setting Up a Reverse Telnet Session to the Catalyst 1900 Switch
Termserver#cat1900 Trying cat1900 (192.168.1.3, 2007)... Open ------------------------------------------------- Catalyst 1900 Management Console Copyright (c) Cisco Systems, Inc. 1993-1997 All rights reserved. Ethernet address: 00-C0-1D-80-C7-5E ------------------------------------------------- 1 user(s) now active on Management Console. Enter password: Termserver#
Now from the terminal server, do a show sessions and notice that each reverse Telnet session has been assigned a connection number (see Example 4-27).
Example 4-27 Connections Numbers Assigned to Each Lab Device
Termserver#show sessions Conn Host Address Byte Idle Conn Name 1 r1 192.168.10.10 0 0 R1 2 r2 192.168.10.10 0 0 r2 3 r3 192.168.10.10 0 0 r3 4 r4 192.168.10.10 0 0 r4 5 r5 192.168.10.10 0 0 r5 6 r6 192.168.10.10 0 0 r6 7 cat1900 192.168.10.10 0 0 cat1900
From this point on, when configuring lab devices, you can access each device by simply entering the connection number associated with the device from the terminal server (that is, 1 to access R1, 2 to access R2, and so on).
You have now successfully completed the configuration of the terminal server. Table 4-1 summarizes the commands to maneuver between the terminal server and the lab routers, as well as manage reverse Telnet connections on the terminal server.
Table 4-1 Chapter Command Summary
Displays all open sessions
disconnect connection #
Disconnects the desired connection
clear line line #
Clears the desired asynchronous line (1 to 16, where 1 = 2001, 2 = 2002 and so on)
Escapes the current session and returns to the terminal server
line 1 16
Enters line configuration mode for asynchronous lines 1 through 16 on the terminal server
line vty 0 4
Enters line configuration mode for vty lines 0 through 4
transport input protocol
Defines what protocols are allowed across the asynchronous or vty lines
ip host [hostname] [port] [ip-address]
Adds an entry to the IP host name table
Copy running-config startup-config
Copies the running configuration to the startup configuration