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This chapter describes how to use the internal packet assembler/disassembler (PAD) facility to make connections with remote devices over the X.25 protocol.
The following sections are provided in this chapter:
For a complete description of the PAD commands in this chapter, refer to the "PAD and X.25 Connection Setup Commands" chapter of the Dial Solutions Command Reference. To locate documentation of other commands that appear in this chapter, use the command reference master index or search online.
For a complete description of each X.3 parameter supported by the standard X.28 mode or Cisco's traditional PAD user interface, see the chapter "X.3 PAD Parameters" in the Dial Solutions Command Reference.
PADs are configured to enable X.25 connections between network devices. A PAD is a device that receives a character stream from one or more terminals, assembles the character stream into packets, and sends the data packets out to a host. A PAD can also do the reverse. It can take data packets from a network host and translate them into a character stream that can be understood by the terminals. A PAD is defined by CCITT Recommendations X.3, X.28, and X.29.
Figure 80 shows a remote X.25 user placing a call through an X.25 switched network, to the internal PAD application on a Cisco 4700-M router, and to an X.25 host located inside a corporate data center.
PADs can also be configured to work with a protocol translation application. Figure 81 shows an example of a remote PC placing an analog modem call to an IP network, connecting to a Cisco 4500-M router, allowing its IP packets to undergo an IP-to-X.25 protocol translation, which in turn communicates with an internal PAD device and establishes a connection with an X.25 host.
The following sections describe how to use the X.28 standard user interface to make X.25 PAD connections:
X.28 emulation is the standard user interface between data terminal equipment (DTE) and a packet assembler/disassembler (PAD). The Cisco IOS software provides an X.28 user emulation mode, which enables you to interact with and control the PAD. During this exchange of control information, messages or commands sent from the terminal to the PAD are called PAD command signals. Messages sent from the PAD to the terminal are called PAD service signals. These signals and any transmitted data take the form of encoded character streams as defined by International Alphabet Number 5.
For asynchronous devices such as terminals or modems to access an X.25 network host, the device's packets must be assembled or disassembled by a PAD device. Using standard X.28 commands from the PAD, calls can be made into an X.25 network, X.3 PAD parameters can be set, or calls can be reset. X.3 is the ITU-T recommendation that defines various PAD parameters used in X.25 networks. There are 22 available X.3 PAD parameters to configure. X.3 PAD parameters are internal variables that define the operation of a PAD. For example, parameter number 9 is the crpad parameter. It determines the number of bytes to add after a carriage return. X.3 parameters can also be set by a remote X.25 host using X.29. (See Figure 82.)
X.28 enables PAD system administrators to dial into X.25 networks or set PAD parameters using the X.28 standard user interface. This standard interface is commonly used in many European countries. It adheres to the X.25 International Telecommunication Union Telecommunication (ITU-T) standards.
The X.28 interface is designed for asynchronous devices that require X.25 transport to access a remote or native asynchronous or synchronous host application. For example, dial-up applications can use the X.28 interface to access a remote X.25 host. X.28 PAD calls are often used by banks to support back office applications such as ATM machines, point of sales authorization devices, and alarm systems. An ATM machine may have an asynchronous connection to an alarm host and a Cisco router. When the alarm is tripped, the alarm sends a distress call to the authorities via the Cisco router and a X.28 PAD call.
Cisco's X.28 PAD calls can be transported over a public packet network, a private X.25 network, the Internet, a private IP-based network, or a Frame Relay network. X.28 PAD can also be used with protocol translation. Protocol translation and VTY asynchronous interfaces enable users to bidirectionally access an X.25 application with the PAD service or other protocols such as Digital Equipment Corporation (DEC), local-area transport (LAT), and transmission control protocol (TCP).
The following optional tasks are described in this section:
Access X.28 mode using the x28 EXEC command. This mode can also be accessed with the autocommand line configuration command. The autocommand command can be assigned to a particular line, range of lines, or login user ID. In this case, when a user connects to the line the user sees an X.28 interface. Using the noescape option with the autocommand feature blocks users from getting into EXEC mode.
The default X.28 router prompt is an asterisk (*). After you see *, the standard X.28 user interface is available. You configure the PAD in this mode.
To enter X.28 mode and set different access and display parameters, use the following commands in EXEC mode:
| Command | Purpose |
|---|---|
x28 escape character-string | Specifies a character string to use to exit X.28 mode and return to EXEC mode. This string becomes an added command to X.28 mode which, when entered by the user, terminates X.28 mode and return to EXEC mode. The default escape string is exit. 1 |
Places the data entered in the network user identification (NUI) facility by the user into the call user data field of the X.25 call request packet.2 | |
x28 profile file-name | Specifies a user-defined X.3 profile. If this option is specified, with a profile name, then the profile is used as the initial set of X.3 parameters.3 |
Reverses the charges of all calls dialed by the local router. The address of the destination device is charged for the call. This is the default configuration. Every call is placed with the reverse charge request set. | |
Display detailed information about the X.25 call connection (for example, address of the remote DTE device and the facility block used). |
Many X.25-related functions can be performed in X.28 mode, such as placing and clearing calls. Table 20 lists the available PAD command signals that can be issued.
In X.28 mode, the are various PAD command signals you can use. You can choose to use the standard or extended command syntax. For example, you can enter the clr command or clear command to clear a call. A command specified with standard command syntax is merely an abbreviated version of the extended syntax version. Both syntaxes function the same.
| Command | Extended Command Variant | Purpose |
break |
| Simulates an asynchronous break. |
call |
| Places a virtual call to a remote device. |
command-signal |
| Specifies a call request without using a standard X.28 command, which is entered with the following syntax: facilities-x121-addressDcall-user-data. The dash (-) and "D" are required keywords. |
clr | clear | Clears a virtual call. |
help |
| Displays help information. |
iclr | iclear | Requests the remote device to clear the call. |
int | interrupt | Sends an Interrupt Packet. |
par? | parameter read | Shows the current values of local parameters. |
prof | profile file-name | Loads a standard or named profile. |
reset |
| Resets the call. |
rpar? | rread | Shows the current values of remote parameters. |
rset? | rsetread | Sets and then read values of remote parameters. |
set |
| Changes the values of local parameters. (See the "Customize X.3 Parameters" section.) |
set? | setread | Changes and then read the values of parameters. |
stat | status | Requests status of a connection. |
selection pad |
| Sets up a virtual call. |
To place a call to another X.25 destination, you specify the destination X.121 address optionally preceded by facility requests and optionally followed by call user data. As of Release 12.0, Cisco only supports the reverse charge and NUI facilities.
To place a call, use the following commands beginning in EXEC mode:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| x28 | Enter X.28 mode. An asterisk prompt will appear. | ||
| call address | Dial the address of the remote interface. |
After you connect to a remote X.25 device, you can clear the connection by using the following commands beginning in EXEC mode:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| Ctrl-p | From the remote host, escape back to the local router. | ||
| clr | Clear the virtual call. |
To set an X.3 PAD parameter from a local terminal, use the following commands beginning in EXEC mode:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| x28 | Enter X.28 mode. | ||
| par | Display the current X.3 PAD parameters. | ||
| set parameter-number: new-value | Change the value of a parameter. | ||
| par | Verify that the new PAD parameter was set correctly. |
Active lines operating in X.28 mode can receive incoming calls from the network, if they do not already have an active call. The user is notified of the call by the X.28 incoming call service signal. This feature extends the traditional capability of reverse PAD connections, which could only be received on lines that were not active.
The criteria to choose the line the call is intended for is the same as for reverse PAD connections. (The rotary is chosen from subaddress portion of the destination address.) Since the normal rotary selection mechanism (which checks whether lines have an active EXEC or not) takes precedence, reverse connections to lines in X.28 mode will only work reliably to rotaries consisting of a single line.
There are several ways you can access X.28 PAD mode on the router:
If an asynchronous line is configured with the autocommand x28 command, the devices connected to the asynchronous line always get X.28 mode. Otherwise, an EXEC session is on the line and the x28 command can be issued to start X.28 mode.
To set this up on the router, following these steps.
Step 1 Enter global configuration mode:
router# configure terminal Enter configuration commands, one per line. End with CNTL/Z.
Step 2 Bring up a one or more asynchronous lines and enter the autocommand x28 command.
router(config)# line 1 2 router(config-line)# autocommand x28
This connection originates from a TCP/IP network. This connection method is used for a two-step connection from an IP device to an X.25 device.
To set this up on the router, following these steps.
Step 1 Telnet to the PAD facility inside the router.
Step 2 Command the PAD to connect to the X.25 device. This is done by configuring a range of VTY lines to contain the autocommand x28 command and the rotary xx command.
router# configure terminal Enter configuration commands, one per line. End with CNTL/Z. router(config)# line vty 0 4 router(config-line)# autocommand x28 router(config-line)# rotary 1 router(config-line)# exit router(config)#
Step 3 Assign an alternate IP address to the rotary port using the ip alias command.
router(config)# ip alias aaa.bbb.ccc.ddd 30xx
In this example, xx is the rotary number assigned. The field aaa.bbb.ccc.ddd is an additional IP address assigned to the router for X.28 PAD mode incoming calls.
Step 4 The remote user accesses X.28 mode on the router by issuing the telnet aaa.bbb.ccc.ddd command from the IP host. If required, login options can be specified on this vty line.
ip-host% telnet 170.62.90.18 Trying 170.62.90.18... Connected to 170.62.90.18. Escape character is '^]'. User Access Verification Username: letmein Password: guessme *
This connection originates from a X.25 network. This is an unlikely scenario since most users are most likely already connected to an X.25 host. However, this configuration is useful getting around security restrictions.
To set this up on the router, following these steps.
Step 1 Configure a range of VTY lines with the autocommand x28 command and the rotary xx command.
router# configure terminal Enter configuration commands, one per line. End with CNTL/Z. router(config)# line vty 0 4 router(config-line)# autocommand x28 router(config-line)# rotary 1
Step 2 The remote user can now access X.28 mode by initiating a connection to the X.21 address AAAAxx, where AAAA is the X.21 address of the router and xx is the rotary number defined in Step 1.
The following examples are provided:
The following examples show two ways to make a call to a remote X.25 host over a serial line. The remote host's interface address is 123456. In the first example, router-A calls router-B using the pad 123456 EXEC command. The second example shows router-A calling router-B using the call 123456 PAD signal command in X.28 mode. Both commands accomplish the same goal.
router-A# pad 123456 Trying 123456...Open router-B> exit [Connection to 123456 closed by foreign host] router-A# x28 * call 123456 COM router-B>
The following examples show two ways to clear a connection with a remote X.25 host. The first example shows router-A disconnecting from router-B using the disconnect command in EXEC mode. The second example shows router-B disconnecting from router-A using the clr command in X.28 mode.
router-A# pad 123456
Trying 123456...Open
router-B> <Enter the escape sequence (for example, press Shift-Ctrl-^-x).>
router-A# disconnect
Closing connection to 123456 [confirm]
router-A#
router-A# x28
* call 123456
COM
router-B> <Press Ctrl-p>
* clr
CLR CONF
*
The following example configures parameter 9 from 0 to 1, which adds one byte after the carriage return. This setting is performed from a local terminal using the set parameter-number: new-value PAD command signal.
router-A# x28 * par PAR 1:1 2:1 3:126 4:0 5:1 6:2 7:2 8:0 9:0 10:0 11:14 12:1 13:0 14:0 15:0 16:127 17:24 18:18 19:2 20:0 21:0 22:0 * set 9:1 * par PAR 1:1 2:1 3:126 4:0 5:1 6:2 7:2 8:0 9:1 10:0 11:14 12:1 13:0 14:0 15:0 16:127 17:24 18:18 19:2 20:0 21:0 22:0 *
The following example shows how to change a local X.3 PAD parameter from a remote X.25 host using X.29 messages, which is a secure way to enable a remote host to gain control of local PAD. The local device is router-A. The remote host is router-B. The parameters listed in the ParamsIn field are incoming parameters, which are sent by the remote PAD. The parameters listed in the ParamsOut field are parameters sent by the local PAD.
router-A# pad 123456
Trying 123456...Open
router-B> x3 2:0
router-B>
router-A# show x25 pad
tty0, connection 1 to host 123456
Total input: 12, control 3, bytes 35. Queued: 0 of 7 (0 bytes).
Total output: 10, control 3, bytes 64.
Flags: 1, State: 3, Last error: 1
ParamsIn: 1:0, 2:0, 3:0, 4:0, 5:0, 6:0, 7:0,
8:0, 9:0, 10:0, 11:0, 12:0, 13:0, 14:0, 15:0,
16:0, 17:0, 18:0, 19:0, 20:0, 21:0, 22:0,
ParamsOut: 1:1, 2:0, 3:2, 4:1, 5:1, 6:0, 7:21,
8:0, 9:1, 10:0, 11:14, 12:1, 13:0, 14:0, 15:0,
16:127, 17:21, 18:18, 19:0, 20:0, 21:0, 22:0,
router-A#
The following example modifies and loads an existing X.25 PAD parameter profile. It accesses the existing PAD profile ppp, changes its padding parameter (specified as 9) to a value of 2, and displays the new parameters using the par command in X.28 mode.
router-A# configure terminal Enter configuration commands, one per line. End with CNTL/Z. router-A(config)# x29 profile ppp 9:2 router-A(config)# end router-A# %SYS-5-CONFIG_I: Configured from console by console router-A# x28 profile ppp * par PAR 1:1 2:1 3:126 4:0 5:1 6:2 7:2 8:0 9:2 10:0 11:14 12:1 13:0 14:0 15:0 16:127 17:24 18:18 19:2 20:0 21:0 22:0
The following example sends an authentication message to a remote X.25 host using the x28 nuicud command in X.28 mode followed by the Ncisc-123456 X.28 command. The network identifier is N. The network user password is cisc. The destination address of the remote device is 123456. The ASCII representation of the user password appears in the call user data field, not in the data packet.
router-A# debug x25 event X.25 special event debugging is on router-A# x28 nuicud * Ncisc-123456 COM router-B> 02:02:58: Serial1: X.25 O P1 Call (16) 8 lci 20 02:02:58: From(3): 222 To(3): 123456 02:02:58: Facilities: (0) 02:02:58: Call User Data (8): 0x01000000xxxxxxxx (pad) 02:02:58: Serial1: X.25 I P2 Call Confirm (5) 8 lci 20 02:02:58: From(0): To(0): 02:02:58: Facilities: (0)
The charges for all outgoing calls made from the local router can be reversed to the destination device using the x28 reverse command. To reverse the charges for only one outgoing call, use the R- address command, which is the standard X.28 reverse charge facility command.
router-A# x28 reverse * exit router-A# x28 * R-123456 COM
Each time a call is made to a remote device, you can specify that detailed information be displayed about the call and the destination device by entering the x28 verbose command. The following example shows reverse charging configured and call user data represented as userdata:
router# x28 verbose * R-111*userdata Called DTE Address : 3001 Facility Block : R Call User Data :userdata COM
Use the help command to get short descriptions of the available parameters.
* help
The "help" PAD command signal consists of the following elements:
<help PAD command signal> <help subject>
where
<help subject> is the identifier for the type of
explanatory information requested
* help break
BREAK Simulate async BREAK
The following sections describe how to configure a PAD using the legacy X.3 PAD user interface. The X.28 user interface is commonly used in many European countries. It adheres to the X.25 International Telecommunication Union Telecommunication (ITU-T) standards.
The following optional configuration tasks are provided:
To display information about packet transmission and X.3 PAD parameter settings and log on to a PAD, use the following commands in EXEC mode:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| show x25 pad | Display information about packet transmission and X.3 PAD parameter settings. | ||
| pad {x121-address | hostname} [/cud text] [/debug] [/profile name] [/quiet message] [/reverse] [/use-map] | Log on to a PAD. |
You can exit a connection and return to the user EXEC prompt at any point.
To open a new connection, first exit the current connection by typing the escape sequence (Ctrl-Shift-6 then x [Ctrl^x] by default) to return to the EXEC prompt, then open the new connection.
You can have several concurrent sessions open and switch between them. The number of sessions that can be open is defined by the session-limit command, which is described in the "Configuring Modem Support and Asynchronous Devices" chapter of this publication and the "Modem Support and Asynchronous Devices Commands" chapter of the Dial Solutions Command Reference.
To switch between sessions by escaping one session and resuming a previously opened session, use the following commands:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| Ctrl-Shift-6 then x (Ctrl^x) by default | Escape the current connection, if you have one open, and return to EXEC mode. | ||
| where | From EXEC mode, list the open sessions. All open sessions associated with the current terminal line are displayed. | ||
| resume [connection] [keyword] | Make the connection. |
The Ctrl^x, where, and resume commands are available with all supported connection protocols.
To exit a PAD session, enter the escape sequence (Ctrl-Shift-6 then x [Ctrl^x] by default) and enter the disconnect command at the EXEC prompt. You can also log off the remote system by issuing the command specific to that system (such as exit, logout, quit, close, or disconnect).
To display information about current open connections, use the following command in user EXEC mode:
| Command | Purpose |
|---|---|
Display information about X.25 PAD connections that are currently open. |
The information includes packet transmissions, X.3 parameter settings, and the current status of virtual circuits.
To set X.3 PAD parameters, use the following commands in EXEC mode:
| Command | Purpose |
|---|---|
resume [connection] [/set parameter:value] or |
The parameters are numbered from 1 through 18. See the "X.3 PAD Parameters" appendix of the Dial Solutions Command Reference for more information.
For an example of setting X.3 PAD parameters, see the next example.
The following example starts a PAD session:
router> pad 123456789 Trying 123456789...Open router2>
The next example illustrates how to reset the outgoing connection default for local echo mode on a router. The /set switch sets the X.3 parameters defined by parameter number and value, separated by a colon.
router> resume 3 /set 2:1
The following are examples of show x25 vc command output for PAD over CMNS, PAD to PAD over X25, and PAD over XOT connections:
router# show x25 vc SVC 1, State: D1, Interface: Ethernet0 Started 00:01:48, last input 00:01:48, output 00:01:48 Line: 0 con 0 Location: console Host: 2193330 connected to 2193330 PAD <--> CMNS Ethernet0 00e0.b0e3.0d62 Window size input: 2, output: 2 Packet size input: 128, output: 128 PS: 2 PR: 3 ACK: 3 Remote PR: 2 RCNT: 0 RNR: no P/D state timeouts: 0 timer (secs): 0 data bytes 54/19 packets 2/3 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0 SVC 1024, State: D1, Interface: Serial1 Started 00:00:07, last input 00:00:26, output 00:00:26 Line: 0 con 0 Location: console Host: 2194443 2191111 connected to 2194443 PAD <--> X25 Window size input: 5, output: 5 Packet size input: 128, output: 128 PS: 0 PR: 0 ACK: 0 Remote PR: 0 RCNT: 0 RNR: no P/D state timeouts: 0 timer (secs): 0 data bytes 0/0 packets 0/0 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0 SVC 1, State: D1, Interface: [172.21.9.7,1998/172.21.9.11,11000] Started 00:06:48, last input 00:06:43, output 00:06:43 Line: 0 con 0 Location: console Host: 219444001 219111 connected to 219444001 PAD <--> XOT 172.21.9.7,1998 Window size input: 2, output: 2 Packet size input: 128, output: 128 PS: 5 PR: 4 ACK: 4 Remote PR: 5 RCNT: 0 RNR: no P/D state timeouts: 0 timer (secs): 0 data bytes
The following is example output for the show x25 pad command:
router# show x25 pad
tty0 (console), connection 1 to host 2194440
Total input: 75, control 2, bytes 3168. Input Queued: 0 of 7 (0 bytes).
Total output: 50, control 2, bytes 52. Output Queued: 0 of 5.
Flags: 1, State: 3, Last error: 1
ParamsIn: 1:0, 2:0, 3:0, 4:0, 5:0, 6:0, 7:0,
8:0, 9:0, 10:0, 11:0, 12:0, 13:0, 14:0, 15:0,
16:0, 17:0, 18:0, 19:0, 20:0, 21:0, 22:0,
ParamsOut: 1:1, 2:0, 3:2, 4:1, 5:1, 6:0, 7:21,
8:0, 9:0, 10:0, 11:14, 12:1, 13:0, 14:0, 15:0,
16:127, 17:21, 18:18, 19:0, 20:0, 21:0, 22:0,
tty18, Incoming PAD connection
Total input: 2, control 2, bytes 54. Input Queued: 0 of 7 (0 bytes).
Total output: 1, control 2, bytes 9. Output Queued: 0 of 5.
Flags: 1, State: 3, Last error: 1
ParamsIn: 1:1, 2:0, 3:2, 4:1, 5:0, 6:0, 7:21,
8:0, 9:0, 10:0, 11:14, 12:0, 13:0, 14:0, 15:0,
16:127, 17:21, 18:18, 19:0, 20:0, 21:0, 22:0,
ParamsOut: 1:1, 2:1, 3:2, 4:1, 5:0, 6:0, 7:4,
8:0, 9:0, 10:0, 11:14, 12:0, 13:0, 14:0, 15:0,
16:127, 17:21, 18:18, 19:0, 20:0, 21:0, 22:0,
PAD calls can be made to destinations that are not reachable over physical X.25 interfaces, but instead over TCP tunnels. PAD calls originating from a router on an IP link can reach an X.25 device. This feature is also known as PAD over XOT. The service pad to-xot command and service pad from-xot global configuration commands enable the PAD over XOT feature. Figure 83 shows PAD calls originating from a router in an IP network reaching a X.25 device.
To allow PAD connections over XOT on the router, use the following commands beginning in privileged EXEC mode:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| configure terminal | Enter global configuration mode. | ||
| service pad [from-xot] [to-xot] | Specify outgoing PAD calls over XOT or incoming XOT to PAD connections. | ||
| x25 host name x121-address | Depending on your application, specify an X.121 address for the host name of the router or an X.25 route pointing out over XOT.1 |
This section provides the following PAD over XOT configuration examples:
The following example enables connections from XOT to a local PAD. Because XOT is a TCP connection, the connection is not tied to an X.25 interface. An X.25 address must be configured for the host name of the router that is accepting the call. In this case, the router answers and clears an incoming PAD call through address 1234.
router(config)# service pad from-xot router(config)# x25 host router-A 1234
The following example accepts an incoming PAD call over XOT to address 12345. The router then translates the call and makes a TCP connection to the device called puli.
router(config)# service pad from-xot router(config)# translate x25 12345 tcp puli
The following example enables outgoing PAD to XOT connections from an asynchronous line or virtual terminal line. A route pointing out over XOT must be configured on the routing table to make a PAD call. This route can also be used for switching.
router(config)# service pad to-xot router(config)# x25 route 1111 xot 2.2.2.2.
X25 synchronous or PAD devices attached to a router in a remote location may need to ensure that outgoing PAD calls use an assigned X.121 address for the calling (source) address or an assigned X.121 address for the called (destination) address.
Normally, the called address is sent by default in the outgoing PAD call. For the source address, the PAD applies the originating interface's address (even if it is NULL) or the X25 host address (for example XOT) as the source address of the call. To override the default behavior and substitute the original X.121 source/destination address in the outgoing PAD calls, use the x25 route command plus the substitute-source and substitute-dest keyword options.
The following example performs address substitution for PAD calls over XOT. See the x25 route command for more information about address substitution.
router(config)# x25 route ^1234 substitute-source 5678 xot 1.1.1.1 [or] router(config)# x25 route ^1234 substitute-dest 5678 int s 1
To verify the source or destination address substitution on the outgoing PAD call, use the debug x25 event command and show x25 vc command.
For example, to substitute the destination address of 8888 to 5678 and replace the default source address of the outgoing PAD call to 1234, enter the following x25 route command:
router(config)# x25 route 8888 substitute-source 1234 substitute-dest 5678 int s 1
Placing a PAD call to destination 8888 will be substituted by 5678 and a source addresss of 1234:
router# pad 8888 Trying 8888...Open
The following is output of an X.25 debug event:
Serial1: X.25 O R1 Call (13) 8 lci 1024 From(4): 1234 To(4): 5678 Facilities: (0) Call User Data (4): 0x01000000 (pad) Serial1: X.25 I R1 Call Confirm (5) 8 lci 1024 From(0): To(0): Facilities: (0)
The following is output from the show x25 vc command:
router# show x25 vc SVC 1024, State: D1, Interface: Serial1 Started 00:23:54, last input 00:00:13, output 00:00:13 Line: 0 con 0 Location: console Host: 456 1234 connected to 5678 PAD <--> X25 Window size input: 2, output: 2 Packet size input: 128, output: 128 PS: 0 PR: 0 ACK: 0 Remote PR: 0 RCNT: 0 RNR: no P/D state timeouts: 0 timer (secs): 0 data bytes 68/958 packets 16/27 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0
In situations where the X.121 calling address is not sufficient to identify the source of the call, you can append a specified value to the calling address using the PAD subaddressing feature. PAD subaddressing allows you to create unique X.121 calling addresses by including either a physical port number or a value specified for a line as a subaddress to the X.121 calling address.
PAD subaddressing enables an X.25 host application to uniquely identify the source of an X.121 call. For example, in some bank security alarm applications, the central alarm host identifies the physical location of the alarm units from subaddressing information contained in the Call Request packet.
Before you can configure PAD subaddressing, you need to configure your router or access server to support X.25. For more information, refer to the Wide-Area Networking Configuration Guide.
To configure PAD subaddressing, use the following commands beginning in privileged EXEC mode:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| configure terminal | Enter global configuration mode. | ||
| line [aux | console | tty | vty] line-number [ending-line-number] | Identify the line(s) whose information will be appended to the X.121 address as the subaddress. | ||
| x25 subaddress {line | number} | Create a unique X.121 calling address by adding either a physical port number or a numeric value for a line as a subaddress to the X.121 calling address. |
The following example shows how to configure subaddressing on vty lines 10 through 20 by appending the line number as a subaddress to the X.121 calling address:
router(config)# line vty 10 20
router(config-line)# x25 subaddress line
The following example shows how to configure subaddressing on the first five tty lines by appending the value "09" as a subaddress to the X.121 calling address of the X.28 connection originating on these lines:
router(config-line)# line 1 5
router(config-line)# x25 subaddress 9
router(config-line)# autocommand x28
You can use the output from the debug x25 event and the show line commands to display information about PAD subaddressing. Once you have configured PAD subaddressing, the output from both of these commands changes to reflect the additional subaddress information.
The following example shows debug x25 event output, where the X.25 address is 12345 and the subaddress for tty line 3 is 09.
router# debug x25 event
Serial1: X.25 O P1 Call (14) 8 lci 1024
From(7): 1234509 To(4): 6789
Facilities: (0)
Call User Data (4): 0x01000000 (pad)
Serial1: X.25 I P2 Call Confirm (5) 8 lci 1024
From (0): to (0):
Facilities: (0)
PAD3: Call completed
The following example shows sample show line output for a router called enkidu, where line 18 has been configured for PAD subaddressing.
router#show line 18TtyTypTx/RxA ModemRotyAccOAccIUsesNoiseOverruns18VTY-----100/0 Line 18, Location: "enkidu", Type: "" Length: 48 lines, Width: 80 columns Baud rate: (TX/RX) is 9600/9600 Status: Ready, Connected, Active, No Exit Banner Capabilities: Line usable as async interface, PAD Sub-addressing usedModem state: Ready
Cisco supports X.29 reselect, which is a standard Triple-X PAD function supported in later versions of the X.3, X.28, and X.29 specifications. X.29 reselect is used in conjunction with mnemonics and autoconnect/autocall to the "first host." X.29 reselect is for security checking and DNS, such as the X.25 naming/selection of destinations within a public or private network. The primary (first) destination host acts much like a RADIUS/TACACS server. At a minimum, both the PAD and the "first host" used in the topology need to support X.29 reselect. X.29 reselect is transparent to network elements or switches. No Cisco IOS commands need to be entered to enable X.29 reselect. It is enabled by default.
Mnemonic addressing enables you to connect to a remote host by using the host's mnemonic address, not the X.121 address. As the number of hosts grows within an X.25 network, system administrators need to remember numerous 14 digit X.121 addresses to connect to multiple host applications. To ease the burden of this administrative overhead, asynchronous PAD users can now access hosts by using mnemonic (abbreviated) addressing.
When the user specifies the mnemonic address in the call X.28 command, the mnemonic gets translated to an X.121 address in the local PAD. The resulting call request contains both the X.121 calling and called addresses.
You can use the following formats:
The following format options and examples are provided.
Format---c <NUI, Facilities>-.<Mnemonic> *<call-user-data>
Description---This is the generalized format of the call command where you can specify network user identification (NUI) and facilities with -.mnemonics and an asterisk (*) before the call user data (CUD). The comma (,) separates individual facility specifications.
Example syntax---Nsmith-.billing*xyz
smith = NUI and no facilities
billing = 31xx4085272478
xyz = call user data (CUD)
Format------c .<Mnemonic> *<call-user-data>
Description---No facilities, with CUD
Example syntax---c .billing*xyz
billing = 31xx4085272478 with CUD of xyz
Format------c <Mnemonic>
Description---No dot, no facilities, no CUD
Example syntax---billing
billing = 31xx4085272478
Format---<Mnemonic>
Description---No dot, no facilities, no CUD
Example syntax---billing
billing = 31xx4085272478
The supported facility codes that can be specified in the call request packet include the following. The X.121 address is a <word> with decimal digits.
| Code | Description |
N <word> | Network User Identification (NUI). |
T <word> | Recognized Private Operating Agency (RPOA). |
R | Reverse charge. |
G <word> | Closed user group (<word> is one or two decimal digits). |
O <word> | Closed user group with outgoing access (<word is one or two decimal digits). |
C | Charging information. |
E <word> | Called address (<word is up to 40 decimal digits). |
F | Fast select with no restrictions. |
S | Reselect prevention. |
Q | Fast select with restrictions. |
Posted: Mon May 3 12:15:16 PDT 1999
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