X.25 Protocols

Document ID: 14190

Contents

Introduction
Prerequisites
      Requirements
      Components Used
      Related Products
      Conventions
Configure
      Network Diagram
      Configurations
Verify
Troubleshoot
      Troubleshooting Commands
Related Information

Introduction

This sample configuration describes how to make outgoing packet assembler/disassembler (PAD) calls on a router when there are no X.25 resources available. To do this, you must initiate an X.25 over TCP/IP (XOT) call to another router that does have access to the X.25 network.

The command to issue to make the outgoing call is service pad to-xot. The sample configuration used here has been configured to put the calling address in the call setup.

For more information on the commands used in this document, please refer to X.25 and LAPB Commands.

Prerequisites

Requirements

Before attempting this configuration, please ensure that you meet these prerequisites:

• A basic knowledge of X.25

• A basic knowledge of configuring X.25

• A basic knowledge of configuring a router as a PAD for XOT

Please refer to the Related Information section of this document for more details.

Components Used

The information in this document is based on these software and hardware versions:

• Cisco IOS® Software Release 12.2(10b)

• Cisco 2503 and 2520 routers

This functionality is available in Cisco IOS Software Releases 11.2 and later.

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Related Products

This configuration can be used with any two routers with one WAN serial interface each. You can use WIC-1T, WIC-2T, and fixed WAN serial interfaces.

Conventions

For more information on document conventions, refer to the Cisco Technical Tips Conventions.

Configure

In this section, you are presented with the information necessary to configure the features described in this document.

The configuration can be split into two steps:

1. Configuring PAD over XOT. This enables PAD calls to destinations that are not reachable over physical X.25 interfaces, but over TCP tunnels.

2. Configuring the X.25 network and the X.25 destination host.

Note: To find additional information on the commands used in this document, use the Command Lookup Tool (registered customers only) .

Network Diagram

This document uses the network setup shown in this diagram:

In this design, the AUX port 0 of the router is used for the connection to the async host. However, you can use the same configuration with an async or modem interface.

Configurations

This document uses these configurations:

• RouterA

• RouterB

• RouterC

service pad to-xot

!---This allows outgoing XOT calls.

service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname RouterA
!
enable password
!
ip subnet-zero
 no ip finger
 no ip domain-lookup
!
x25 routing

!--- This enables X.25 switching.

!
!
!
interface Serial0
 description Link to IP network for XOT session
 ip address 172.17.200.1 255.255.255.252
 no fair-queue
 clockrate 64000
!
ip classless
!
x25 route ^901 xot 172.17.200.2

!--- This is the route statement to switch the PAD call.

x25 host RouterA 900

!--- This can be used for the calling address field (the hostname must be used).

!
line con 0
 exec-timeout 0 0
 password 
 length 0
 transport input none
line aux 0
 x25 subaddress 4

!--- This is the subaddress to use for the calling field.

 autocommand x28

!--- This sets the async user in X.28 mode to initiate PAD calls.

line vty 0 4
 password 
 login
!
end

service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname RouterB
!
enable password 
!
x25 routing

!--- This enables X.25 switching.

interface Serial0
 description link to IP network to terminate XOT session
 ip address 172.17.200.2 255.255.255.252
!
!
interface Serial1
 description X25 link to access X25 network
 no ip address
 encapsulation x25 dce
 clockrate 64000
!
x25 route ^901 interface Serial1

!--- This is the route statement to switch the XOT call.

line con 0
 exec-timeout 0 0
 password 
 length 0
 transport input none
line aux 0
line vty 0 4
password 
login
end

service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname RouterC
!
enable password xxxxxx
!
!
interface Serial1
 no ip address
 encapsulation x25
 x25 address 901

!--- This is the description of the X.25 link to access the X.25 network. 
!--- It also serves as the X.25 host.

!
line con 0
 exec-timeout 0 0
line aux 0
line vty 0 4
 password xxxxx
 login
!
end

Verify

This section provides information you can use to confirm your configuration is working properly.

Certain show commands are supported by the Output Interpreter Tool (registered customers only) , which allows you to view an analysis of show command output.

Use these commands to verify your configuration:

• show line—Check the line status. In our current example, this goes from the AUX port to tty4.

• show x25 route—Check whether the route statement is correct.

• show x25 pad—Display the X.3 parameters negotiated between the PAD and the host.

• show x25 vc—Check XOT virtual circuit (VC) status.

• show debug—Display the current state of tracing.

This show line command output shows the line AUX is connected to the async host in RouterA:

RouterA# show line
   Tty Typ     Tx/Rx    A Modem  Roty AccO AccI   Uses   Noise  Overruns   Int
*    0 CTY              -    -      -    -    -     18       0     0/828947   -
  Ready
*    1 AUX   9600/9600  -    -      -    -    -     13       0     0/0       -
  Ready
     2 VTY              -    -      -    -    -      3       0     0/0       -
  Ready
     3 VTY              -    -      -    -    -      0       0     0/0       -
  Idle
     4 VTY              -    -      -    -    -      0       0     0/0       -
  Idle
     5 VTY              -    -      -    -    -      0       0     0/0       -
  Idle
     6 VTY              -    -      -    -    -      0       0     0/0       -
  Idle

This show x25 route command output shows the XOT information in RouterA. It says that any packet from RouterA with an X.25 address that begins with 901 should be routed to the IP address 172.17.200.2, which is the IP address of the remote RouterB.

 RouterA# show x25 route
  #  Match                         Substitute          Route to
  1  dest ^901                                         xot 172.17.200.2
   

This show x25 pad command output shows whether it is an incoming or outgoing PAD connection, and what its parameters are:

RouterA# show x25 pad
tty1, connection 1 to host 901
Total input: 15, control 2, bytes 96, drops 0. Input Queued: 0 of 7 (0 bytes).
Total output: 21, control 2, bytes 21. 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, 3:126, 4:1, 5:1, 6:2, 7:21,
    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,

This show x25 vc command output displays the switched virtual circuit 1 (SVC1) created, who originated the call (Line: 1 aux 0), and to which destination (Host: 901). It also shows the source, the destination X.25 address, and the PAD to XOT information (90004 connected to 901 PAD <--> XOT 172.17.200.2,1998).

RouterA# show x25 vc
SVC 1,  State: D1,  Interface: [172.17.200.2,1998/172.17.200.1,11042]
  Started 00:01:38, last input 00:01:29, output 00:01:29

  Line: 1   aux 0    Location:  Host: 901
  90004 connected to 901 PAD <--> XOT 172.17.200.2,1998

  Window size input: 2, output: 2
  Packet size input: 128, output: 128
  PS: 7  PR: 7  ACK: 7  Remote PR: 7  RCNT: 0  RNR: no
  P/D state timeouts: 0  timer (secs): 0
  data bytes 75/96 packets 23/15 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0 

This show x25 vc command output displays the SVC1 created with the source X.25 address (9004) and the destination X.25 address (901):

RouterC# show x25 vc
SVC 1,  State: D1,  Interface: Serial1
  Started 00:04:23, last input 00:04:17, output 00:04:17

  Line: 5   vty 0    Location:  Host: 90004
  90004 connected to 901 PAD <--> X25

  Window size input: 2, output: 2
  Packet size input: 128, output: 128
  PS: 1  PR: 1  ACK: 1  Remote PR: 1  RCNT: 0  RNR: no
  P/D state timeouts: 0  timer (secs): 0
  data bytes 86/69 packets 9/17 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0

Troubleshoot

This section provides information you can use to troubleshoot your configuration.

Configure timestamps in the global configuration as shown:

service timestamps debug datetime msec
service timestamps log datetime msec

When you configure these two commands, the output of debug commands is more accurate because it is displayed with timestamps in milliseconds.

Troubleshooting Commands

Certain show commands are supported by the Output Interpreter Tool (registered customers only) , which allows you to view an analysis of show command output.

Note: Before issuing debug commands, please see Important Information on Debug Commands.

• debug modem—Observe modem line activity on server.

• debug pad—Observe debugs for all PAD connections.

• debug x25 event—Monitor all X.25 traffic.

This is an example of the show debug command output:

   RouterA# show debug
   General OS:
    Modem control/process activation debugging is on
   X.29 PAD:
    X25 PAD debugging is on
   X.25:
    X.25 special event debugging is on

Output of debug on RouterA and RouterC During Call Initiation

This debug output is shown when you initiate the call:

RouterA#
*Mar  2 06:10:04.336: TTY1: EXEC creation
*Mar  2 06:10:04.336: TTY1: create timer type 1, 600 seconds, trying IP address 172.17.200.2
*Mar  2 06:10:07.148: [172.17.200.2,1998/172.17.200.1,11041]: XOT O P2 Call (19)8 lci 1
*Mar  2 06:10:07.152:   From (5): 90004 To (3): 901

!--- The async host initiates a session to host 901.

*Mar  2 06:10:07.156:   Facilities: (6)
*Mar  2 06:10:07.156:     Packet sizes: 128 128
*Mar  2 06:10:07.160:     Window sizes: 2 2
*Mar  2 06:10:07.160:   Call User Data (4): 0x01000000 (pad)
*Mar  2 06:10:07.228: [172.17.200.2,1998/172.17.200.1,11041]: XOT I P2 Call Confirm (11) 8 lci 1

!--- RouterA acts as a PAD and encapsulates the X.25 packet into an IP packet.
 
*Mar  2 06:10:07.232:   From (0):  To (0):
*Mar  2 06:10:07.232:   Facilities: (6)
*Mar  2 06:10:07.236:     Packet sizes: 128 128
*Mar  2 06:10:07.236:     Window sizes: 2 2
*Mar  2 06:10:07.240: PAD1: Call completed

!--- The call is established with the host 901.

*Mar  2 06:10:07.244: PAD1: Control packet received.
*Mar  2 06:10:07.256: TTY1: pause timer type 1 (OK)
*Mar  2 06:10:07.256: PAD1: Input X29 packet type 4 (Read X.3 param) len 1
*Mar  2 06:10:07.260: PAD1: Output X29 packet type 0 (Parameter indication) len45
    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,
*Mar  2 06:10:07.324: PAD1: Control packet received.
*Mar  2 06:10:07.332: PAD1: Input X29 packet type 6 (Set and Read) len 9 2:0, 4:1, 15:0, 7:21,
*Mar  2 06:10:07.336: PAD1: Output X29 packet type 0 (Parameter indication) len9 2:0, 4:1, 15:0, 7:21,

This debug output shows what happens on the RouterC side, which acts as an X.25 host with an X.25 address of 901, when the call is established:

RouterC#
*Mar  2 01:14:45.813: Serial1: X.25 I R1 Call (13) 8 lci 1
*Mar  2 01:14:45.813:   From (5): 90004 To (3): 901
*Mar  2 01:14:45.817:   Facilities: (0)
*Mar  2 01:14:45.821:   Call User Data (4): 0x01000000 (pad)
*Mar  2 01:14:45.829: Serial1: X.25 O R1 Call Confirm (3) 8 lci 1
*Mar  2 01:14:45.833: TTY5: EXEC creation
*Mar  2 01:14:45.841: TTY5: set timer type 10, 30 seconds
*Mar  2 01:14:48.673: TTY5: create timer type 1, 600 seconds
*Mar  2 01:14:50.137: TTY5: set timer type 10, 30 seconds

Output of debug on RouterA and RouterC During the Call Disconnection

This debug output shows the call disconnection in RouterA:

RouterA#
*Mar  2 06:20:14.260: PAD1: Control packet received.
*Mar  2 06:20:14.264: PAD1: Input X29 packet type 1 (Inv to clear) len 1 Invite Clear
*Mar  2 06:20:14.268: TTY1: resume timer type 1 (OK)
*Mar  2 06:20:14.268: TTY1: no timer type 4 to destroy
*Mar  2 06:20:14.272: PAD: Connection closed Cause: 0 Diag: 0

!--- The call is disconnected when the TTY session time expires.

*Mar  2 06:20:14.272: [172.17.200.2,1998/172.17.200.1,11041]: XOT O P4 Clear (5)8 lci 1
*Mar  2 06:20:14.276:   Cause 0, Diag 0 (DTE originated/No additional information)
*Mar  2 06:20:14.280: pad_clear_tx: context 3B9690, packet 33F6D8
*Mar  2 06:20:14.284: PAD1: Closing connection to .  In 87/10, out 15/15
*Mar  2 06:20:14.328: <detached>: XOT I P6 Clear Confirm (3) 8 lci 1
*Mar  2 06:20:20.100: TTY1: timer type 1 expired
*Mar  2 06:20:20.100: TTY1: Exec-timeout expired
*Mar  2 06:20:20.104: TTY1: destroy timer type 1
*Mar  2 06:20:20.120: TTY1: Line reset by "Exec"
*Mar  2 06:20:21.120: TTY1: Modem: (unknown)->READY
*Mar  2 06:20:21.120: TTY1: no timer type 0 to destroy
*Mar  2 06:20:21.124: TTY1: no timer type 1 to destroy
*Mar  2 06:20:21.124: TTY1: no timer type 3 to destroy
*Mar  2 06:20:21.128: TTY1: no timer type 4 to destroy
*Mar  2 06:20:21.128: TTY1: no timer type 2 to destroy

This debug output shows what happens on the RouterC side when the call gets disconnected:

RouterC#
*Mar  2 01:24:48.725: TTY5: timer type 1 expired
*Mar  2 01:24:48.725: TTY5:  Exec timer (continued)
*Mar  2 01:24:52.737: TTY5: timer type 1 expired
*Mar  2 01:24:52.737: TTY5: Exec-timeout expired
*Mar  2 01:24:52.741: TTY5: destroy timer type 1
*Mar  2 01:24:52.745: TTY5: Line reset by "Virtual Exec"
*Mar  2 01:24:52.745: TTY5: Modem: (unknown)->READY
*Mar  2 01:24:52.749: TTY5: no timer type 0 to destroy
*Mar  2 01:24:52.749: TTY5: no timer type 1 to destroy
*Mar  2 01:24:52.753: TTY5: no timer type 3 to destroy
*Mar  2 01:24:52.753: TTY5: no timer type 4 to destroy
*Mar  2 01:24:52.753: TTY5: no timer type 2 to destroy
*Mar  2 01:24:52.917: Serial1: X.25 I R1 Clear (5) 8 lci 1
*Mar  2 01:24:52.917:   Cause 0, Diag 0 (DTE originated/No additional information)
*Mar  2 01:24:52.921: Serial1: X.25 O R1 Clear Confirm (3) 8 lci 1

Related Information

• Configuring a Router as a PAD for XOT to an Asynchronous Host
• Accepting Incoming PAD Calls without an X.25 Interface
• Cisco IOS Release 12.2 Configuration Guides and Command References
• Command Lookup Tool (registered customers only)
• X.25 Technical Support
• Technical Support - Cisco Systems