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Configuring a Modem for the Cisco AccessPath Integrated Access System

Configuring a Modem for the Cisco AccessPath Integrated Access System

In order to access the AccessPath system shelves remotely, you must configure a modem for an out-of-band connection to the Failsafe/Console Management Shelf.

The configuration is a two step process. First, you configure modem support in line configuration mode on the Failsafe/Console Management Shelf Auxiliary 0 port. You will use a set of core commands to set line speed, enable flow control, and enable the modem to initiate outgoing calls or accept incoming calls.

In the second part of the modem configuration process, you will configure the modem itself to function with the Failsafe/Console Management Shelf. You can manually configure modems, or you can have the Failsafe/Console Management Shelf automatically discover and configure modem initialization strings for use with common modems.

This chapter describes the following tasks:

Configuring Auxiliary 0

As described in Chapter 4, you must configure the lines to which you attach modems in order to allow dialin access.

To do this, enter the enabled mode on the Auxiliary 0 port of the Failsafe/Console Management Shelf: 

FC/M_Shelf> enable
Password:
FC/M_Shelf# line aux 0
Enter configuration commands, one per line. End with CNTL/Z.
FC/M_Shelf(config)# line 1 X (X = the highest number of lines the router has; 8 or 16)
FC/M_Shelf(config-line)#

After you enter line configuration mode for Auxiliary 0, configure it using the commands listed in Table 6-1.


Table 6-1: Required Modem Commands
Command Purpose
speed 38400 Sets line speed to the highest common speed for the modem and the Failsafe/Console Management Shelf's auxiliary port. 1
flowcontrol hardware Sets RTS/CTS flow control on the line.
modem inout Configures the line to drop the connection when the carrier detect (CD) signal is lost (cycle DTR to close the connection). The modem dialin command can be used instead of the modem inout command to enhance security because the modem dialin command restricts outgoing connections from the Failsafe/Console Management Shelf to the modem. Use the modem inout command during setup so that you can configure the modem from the Failsafe/Console Management Shelf, and change to the modem dialin command when testing is completed.

1 Cisco Systems assumes that your modem supports flow control. Refer to your modem documentation to learn whether this assumtion is correct, and to learn the maximum transmission speed of your modem.

The speeds for the modem and auxiliary port on the Failsafe/Console Management Shelf are not identical. The modem should be set to 9600 bps; the Failsafe/Console Management Shelf's auxiliary port defaults to a line speed of 38400 bps.

To proceed with the previous example, which illustrates how to enter line configuration mode, the following example shows how to configure the commands listed in Table 6-1:

FC/M_Shelf(config-line)# speed 38400
FC/M_Shelf(config-line)# flowcontrol hardware
FC/M_Shelf(config-line)# modem inout

The preceding examples configure your auxiliary port to support modems.

For testing purposes, enter a password and login local command, although you remove these later:

FC/M_Shelf(config-line)# password test_password
FC/M_Shelf(config-line)# login local

Configuring the Modem

When you configure modems to function with the Cisco AccessPath Integrated Access System, you must provide initialization strings and other settings on the modem to tell it how to function with the Failsafe/Console Management Shelf.

This section describes the tasks required to configure modems that are externally attached to the AccessPath system and includes the following sections:

Communicating with the Modem

Before you can configure the modem, you must establish communication with it, which requires terminal access to the modem's command environment. The process of manually configuring a modem is described in the following sections:

Establishing a Direct Telnet Session to the Modem

You communicate with the modem by establishing a direct Telnet session from AccessPath system asynchronous lines to the modem.

Note This process is also referred to as reverse Telnet. The term reverse Telnet means that you are initiating a Telnet session out the asynchronous line, instead of accepting a connection in to the line (which is a forward connection).

To establish a direct Telnet session to a modem, determine the IP address of your LAN (Ethernet) interface, then enter a Telnet command to port 2000 + n on the Failsafe/Console Management Shelf, where n is the line number to which the modem is connected. For example, to connect to the modem attached to line 1, enter the following command from an EXEC session on the Failsafe/Console Management Shelf: 

Router# telnet 172.16.1.10 2001        
Trying 172.16.1.10, 2001 ... Open

This example enables you to communicate with the modem online 1 using the AT (attention) command set defined by the modem vendor.

Time Saver Use the ip host configuration command to simplify direct Telnet sessions with modems. The ip host command maps an IP address of a port to a device name. For example, the modem1 2001 172.16.1.10 command enables you to enter modem1 to initiate a connection with the modem, instead of repeatedly entering telnet 172.16.1.10 2001 each time you want to communicate with the modem.

If you are unable to connect to the modem, check the following:


  1. Issue the show users EXEC command. It should not indicate the line is in use.

  2. Verify that the line is configured for modem inout.

  3. Issue the show line EXEC command. The output should contain the following two lines: 
Modem state: Idle         
Modem hardware state: CTS noDSR  DTR RTS

  1. Check to see if the virtual terminal connections to lines in the Failsafe/Console Management Shelf require passwords. See Chapter 7 for additional information about assigning passwords to virtual terminals.

  2. Check to see if the speed between the modem and the Failsafe/Console Management Shelf are the same. They are probably different. If they are different, switch off the modem, then switch it back on. This should match the speed of the modem with the speed of the Failsafe/Console Management Shelf.

Testing the Modem Connection

After you make a direct Telnet connection to the modem, you need to test the connection. Send the modem the AT command to request its attention. It should respond with OK. For example: 

at 
OK

If the modem does not reply to the AT command, check the following:


  1. Look at the output of the show line 1 command. If it displays "no CTS" for the modem hardware state, the modem is not connected, powered on, and waiting for data, or the modem might not be configured for hardware flow control.

  2. Check your cabling and the modem configuration (echo or result codes might be off). Enter the appropriate AT modem command to view the modem configuration, or enter the command at&f to return to factory defaults. Refer to your modem documentation to learn the appropriate AT command to view your modem configuration.

Suspending and Terminating Telnet Sessions

The direct Telnet session must be terminated before the line can accept incoming calls. If you do not terminate the session, it will be indicated in the output of the show users command when it returns a modem state of ready if the line is still in use. If the line is no longer in use, the output of the show line value command will return a state of idle.

Terminating the Telnet session requires first suspending it, then disconnecting it. To suspend a Telnet session, enter the escape sequence Ctrl-Shift-6 x (press Control-Shift-6, let go, then press x). Enter the disconnect EXEC command to terminate the telnet session.

Note Ensure that you can reliably issue the escape sequence to suspend a Telnet session. Some terminal emulator packages have difficulty sending the Ctrl-Shift-6 x sequence. Refer to your terminal emulator documentation for more information about escape sequences.

To suspend and then disconnect a Telnet session, perform the following steps:

Step 1 Suspend the Telnet session by entering Ctrl-Shift-6 x:

Step 2 Enter the where EXEC command to check for open sessions:

Step 3 After suspending a session with one modem, you can connect to another modem (then suspend it):

Step 4 To disconnect (completely close) a session, issue the disconnect EXEC command:

Note Before attempting to allow inbound connections, make sure you close all open connections to the modems attached to the AccessPath system. If you have a modem port in use, the modem will not accept a call properly.

Automatically Configuring Your Modem

The Cisco IOS software can issue initialization strings automatically for most types of modems. A modem initialization string is a series of parameter settings that are sent to your modem to configure it to interact with the Failsafe/Console Management Shelf in a specified way. The Cisco IOS software defines seven initialization strings that have been found to properly initialize most modems so that the modems function properly with Cisco access servers. These initialization strings have the following names:

If you do not know which of these modem strings is appropriate for your modems, issue the modem autoconfigure discovery line configuration command, as shown in the following example: 

2511# configure terminal 
2511(config)# line 1 16
2511(config-line)# modem autoconfigure discovery 
2511(config-line)# Ctrl-Z
2511# copy running-config startup-config

The Cisco IOS software first tries the first of these strings to see if the modem initializes properly. If not, the Cisco IOS software cycles to the next string and repeats the process until the appropriate string is found. If none of the strings properly initializes the modem, you must manually configure the modem (refer to "Manually Configuring the Modem" later in this chapter).

If you know that your modem can be configured using an initialization string from one of these scripts, you can issue the modem autoconfigure type type command, where type is one of the strings in the preceding list. If you list a specific modem type, initialization proceeds more quickly.

The following example shows how to enter line configuration mode and issue the modem autoconfigure type type command for a US Robotics Sportster modem. 

2511(config-line)# modem autoconfigure type usr_sportster

For more information about the recommended strings for any type of modem, refer to the section "Sample Modem Strings" in the appendix "Configuring Modem Support and Chat Scripts" in the Access Services Command Reference. If you have access to Cisco Connection Online (CCO), you can also access the following URL for more information: http://www.cisco.com/warp/customer/76/4.htm.l.

Note that these URLs are subject to change without notice. If you need assistance, see the section "Cisco Connection Online" in the chapter "About This Guide."

Manually Configuring the Modem

If you cannot configure the modem automatically, you must configure it manually. The following sections describe how to manually configure an externally attached modem:

Configuring Modem Initialization Strings

This section describes how to determine the correct initialization string for your modem and configure your modem with it.

Modem command sets vary widely. Although most modems use the Hayes command set (prefixing commands with AT), Hayes-compatible modems do not use identical AT command sets.

Refer to your modem manufacturer's documentation to learn how to examine the current and stored configuration of the modem you are using. Generally, you enter AT commands such as &v, i4, or *o to view, inspect, or observe the settings.

Note You can use AT&F as a basic modem initialization string in most cases.
Determining the Modem Initialization String

A sample modem initialization string for a US Robotics Courier modem is as follows: 

&b1&h1&r2&c1&d3&m4&k1s0=1

The modem initialization strings enable the functions defined in the following sections:

Time Saver Initialization strings for other modems are listed in the appendix "Configuring Modem Strings and Chat Scripts" in the Access Services Command Reference and on Cisco Connection Online (CCO) in Tech Tips (http://www.cisco.com/kobayashi/Tech_root.shtm). Note that these URLs are subject to change without notice.
Locking the Port Speed

Lock the speed of the modem to the speed of the auxiliary port on the Failsafe/Console Management Shelf.

Note Make sure to turn off automatic baud rate detection because the modem speeds must be set to a fixed value.

Modems differ in the method they use to lock the EIA/TIA-232 (serial) port speed. In the modem documentation, vendors use terms such as, port-rate adjust, speed conversion, or buffered mode. Enabling error correction often puts the modem in the buffered mode. Refer to your modem documentation to see how your modem locks speed (check the settings &b, \j, &q, \n, or s-register settings).

Setting Hardware Flow Control (RTS/CTS)

Ready-to-send (RTS) and clear-to-send (CTS) signals must be used between the modem and the Failsafe/Console Management Shelf to control the flow of data. Misconfiguring flow control for software or setting no flow control can result in hung sessions and loss of data. Modems differ in the method they use to enable hardware flow control. Refer to your modem documentation to see how to enable hardware flow control (check the settings ', &e, &k, &h, &r, or s-register).

Ensuring Correct DCD Operation

The modem must use the data carrier detect (DCD) wire to indicate to the Failsafe/Console Management Shelf when a session has been negotiated and is established with a remote modem. Most modems use the setting &c1. Refer to your modem documentation for the DCD settings used with your modem.

Ensuring Proper DTR Interpretation

The modem must interpret a toggle of the data terminal ready (DTR) signal as a command to drop any active call and return to the stored settings. Most modems use the settings &d2 or &d3. Refer to your modem documentation for the DTR settings used with your modem.

Answering Calls on the First Ring

If a modem is used to service incoming calls, it must be configured to answer a call after a specific number of rings. Most modems use the setting s0=1 to answer the call after one ring. Refer to your modem documentation for the settings used with your modem.

Checking Other Modem Settings

This section defines other settings that might be needed or desirable depending on your modem.

Best Error Correction

Error correction can be negotiated between two modems to ensure a reliable data link. Error correction standards include LAPM and MNP4. V.42 error correction allows either LAPM or MNP4 error correction to be negotiated. Modems differ in the way they enable error correction. Refer to your modem documentation for the error correction methods used with your modem.

Best Data Compression

Data compression can be negotiated between two modems to allow for greater data throughput. Data compression standards include V.42 bis and MNP5. Modems differ in the way they enable data compression. Refer to your modem documentation for the data compression settings used with your modem.

Initializing the Modem

Refer to this section if you could not or chose to not initialize your modems automatically, as described in the "Automatically Configuring Your Modem" section.

After the modem initialization string has been determined, perform the following steps to configure the modem. This example configures a US Robotics Courier modem on line 1 (decimal number 2000 + line number 1 = 2001):

Step 1 Map a host name to a decimal port. The port number is 200x, plus the number of the TTY line. The following example maps port 2001 to the IP address of the Ethernet0 interface on the Failsafe/Console Management Shelf (172.16.1.10):

Step 2 Establish a direct Telnet session to the modem:

Step 3 Optionally, return the modem to its factory defaults:

Step 4 Configure the modem with an initialization string. The following example string is for a US Robotics Courier modem:

Step 5 Store the modem settings in NVRAM on the modem:

Note Some modems need to be "strapped" so that they start up with saved settings when powered on, rather than using defaults. You should make sure your modem is strapped accordingly.

Step 6 Suspend and disconnect your Telnet session:

Time Saver The script-reset line configuration command can automate the configuration of your modems. See the publication Access Services Configuration Guide, or the "Technical Tips" section on CCO for more information.

Testing the Dialin Connection

The Failsafe/Console Management Shelf and modem are now correctly configured for dialin access. Before configuring any additional protocols for the line (such as SLIP, PPP, or ARA), test the dialin connection.

Note The same configuration issues exist between the client data terminal equipment (DTE) and client modem. Make sure you have the correct EIA/TIA-232 cabling and modem initialization string for your client modem.

The following is an example of a successful connection from a PC using a U.S. Robotics Courier modem to dial in to the Failsafe/Console Management Shelf: 

at&f&c1&d3&h1&r2&b1&m4&k1&w
OK
atdt9,5551234
CONNECT 14400/ARQ/V32/LAPM/V42BIS
User Access Verification
Username: janedoe 
Password:
nas01>

When the modem has been tested and is functional, you may issue the following commands to remove the special settings we placed on the auxiliary port for testing purposes.

FC/M_Shelf(config-line)# line aux 0
FC/M_Shelf(config-line)# modem dialin
FC/M_Shelf(config-line)# login authentication ADMIN
FC/M_Shelf(config-line)# no password
FC/M_Shelf(config-line)# end
FC/M_Shelf(config-line)#

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