X.25 Protocols

Document ID: 9201

Contents

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

Introduction

This document describes the use of Annex G (X.25 over Frame Relay) to facilitate the migration from an X.25 backbone to a Frame Relay backbone. This feature was introduced in Cisco IOS® Software Release 12.0(3)T and is available on the platforms listed in the Annex G (X.25 over Frame Relay) document.

The use of X.25 as a network backbone is becoming obsolete as modern networks change their backbones to newer technologies such as Frame Relay, ATM, and IP. Annex G (X.25 over Frame Relay) facilitates the migration from an X.25 backbone to a Frame Relay backbone by permitting encapsulation of International Telecommunication Union Telecommunication Standardization Sector (ITU-T) X.25/X.75 traffic within a Frame Relay connection.

Annex G was developed to accommodate the many Cisco customers in Europe, where IP is not so common and X.25 continues to be a popular protocol.

With Annex G, the process of transporting X.25 over Frame Relay has been simplified by allowing direct X.25 encapsulation over a Frame Relay network.

This process is largely achieved using X.25 profiles, which were created to streamline X.25 and Link Access Procedure, Balanced, (LAPB) configuration. X.25 profiles can contain existing X.25 and LAPB commands and—once created and named—can be simultaneously associated with more than one Frame Relay data-link connection identifier (DLCI) connection, using just the profile name.

X.25 Layers 2 and 3 are supported transparently over Annex G. LAPB treats the Frame Relay network like an X.25 network link and passes all of the data and control messages over the Frame Relay network.

Prerequisites

Requirements

Readers of this document should have a basic understanding of the following:

• X.25

• Frame Relay

Components Used

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

• All the routers (Cisco 2500 Routers) in this document use Cisco IOS Software Release 12.2(10b).

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.

Conventions

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

Configure

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

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 the diagram below.

Configurations

This document uses the configurations shown below.

• X.25-1 Router

• X.25-2 Router

• X.25-3 Router

• X.25-4 Router

!
version 12.2
!
interface Serial0
 ip address 10.0.0.2 255.255.255.240
 no ip mroute-cache
 encapsulation x25

!--- Specify a serial interface's operation
!--- as an X.25 device.
!--- Default X.25 encapsulation mode is "dte".

  bandwidth 64
 x25 address 1234

!--- Set the X.121 address.

 x25 map ip 10.0.0.1 4321 broadcast

!--- Set up the LAN protocols-to-remote host
!--- mapping. "Broadcast" causes the Cisco IOS
!--- Software to direct any broadcasts sent
!--- through this interface to the specified
!--- X.121 address.

!
line vty 0 4
 password xxx
 login
!

!
version 12.2
!
x25 routing

!--- X.25 local switching.

!
x25 profile foo dte

!--- Configure an X.25 profile indicating
!--- a DTE interface.

 x25 address 1111

!--- Set the X.121 address.

 x25 win 7

!--- Set the default number of packets that
!--- a virtual circuit can receive before
!--- sending an X.25 acknowledgment.

 x25 wout 7

!--- Set the default number of packets that
!--- a virtual circuit can send before
!--- waiting for an X.25 acknowledgment.
!--- Usually, "x25 win" and "x25 wout" are set
!--- to the same value.

 lapb T1 3200

!---  Set the "lapb" retransmission timer period.

!
interface Serial0
 no ip address
 encapsulation frame-relay IETF

!--- Enable Frame Relay encapsulation.
!--- The IETF keyword sets the encapsulation
!--- method to comply with the Internet 
!--- Engineering Task Force (IETF) standard.

 frame-relay lmi-type ansi

!--- Configure an interface for the ANSI
!--- Annex D LMI type.

 frame-relay interface-dlci 100 

!--- Assign a DLCI to a specified Frame Relay
!--- sub-interface on the router.

  x25-profile foo 

!--- Assign the named X.25 profile to the DLCI.

!
interface Serial1
 no ip address
 no ip mroute-cache
 encapsulation x25 dce

!--- Specify a serial interface's operation
!--- as an X.25 DCE device.

 bandwidth 64
 clock rate 64000
!
x25 route ^1234 interface Serial1

!--- Any call with a destination address
!--- beginning with 1234 that is received
!--- on an interface other than Serial1
!--- is forwarded to Serial1.

x25 route ^4321 interface Serial0 dlci 100

!--- Route the X.25 call to the specified
!--- Annex G link.

!

!
version 12.2
!
x25 routing
!
x25 profile bar dce

!--- Configure an X.25 profile indicating
!--- a DCE interface.

 x25 address 2222
 x25 win 7
 x25 wout 7
 lapb T1 3200
!
interface Serial0
 no ip address
 no ip mroute-cache
 encapsulation x25
!
interface Serial1
 no ip address
 encapsulation frame-relay IETF
 frame-relay lmi-type ansi
 frame-relay interface-dlci 110
  x25-profile bar
!
x25 route ^4321 interface Serial0

!--- Any call with a destination address
!--- beginning with 4321 that is received 
!--- on an interface other than Serial0
!--- is forwarded to Serial0.

x25 route ^1234 interface Serial1 dlci 110
!

!
version 12.2
!
interface Serial0
 ip address 10.0.0.1 255.255.255.240
 no ip mroute-cache
 encapsulation x25 dce
 bandwidth 64
 x25 address 4321
 x25 map ip 10.0.0.2 1234 broadcast
 clock rate 64000
!

Verify

This section provides information that you can use to verify that your network is operating 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.

• ping—Check host reachability and network connectivity.

• pad—Log on to a PAD. Refer to the Command Reference for more details.

• show x25 context—View operating configuration status details of an Annex G DLCI link. Refer to the Command Reference for more details.

• show x25 vc—View information about X.25 virtual circuits. Refer to the Command Reference for more details.

• show x25 profile—View the details of X.25 profiles configured on your router. Refer to the Command Reference for more details.

• clear x25—Restart an X.25 service. Refer to the Command Reference for more details.

The outputs shown below are the result of entering these commands on the devices used in this sample configuration

X.25-1# ping 10.0.0.1
Type escape sequence to abort.
   Sending 5, 100-byte ICMP Echos to 10.0.0.1, timeout is 2 seconds:
   !!!!!
   Success rate is 100 percent (5/5), round-trip min/avg/max = 128/128/132 ms

X.25-3# show x25 profile
X.25 profile name: bar
   Number of references: 1
   In use by:
   Annex G: Serial1 DLCI 110
   PROFILE DCE, address 2222, state R/Inactive, modulo 8, timer 0
   Defaults: idle VC timeout 0
   input/output window sizes 7/7, packet sizes 128/128
   Timers: T10 60, T11 180, T12 60, T13 60
   Channels: Incoming-only none, Two-way 1-1024, Outgoing-only none
   LAPB DCE, modulo 8, k 7, N1 default, N2 20
   T1 3200, T2 0, interface outage (partial T3) 0, T4 0

X.25-r4# clear x25 serial 0
Force Restart [confirm]
X.25-r4#

Troubleshoot

This you can use the following information to troubleshoot your configuration.

Troubleshooting Commands

This section provides debug commands you can use to troubleshoot your X.25 configuration.

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

• debug x25 events—Display all X.25 traffic without data and relative rate (RR) packets. Refer to the Command Reference for more details.

• debug x25 annexg—Display information about interfaces running an X.25 over Frame Relay session. Refer to the Command Reference for more details.

The following is sample output from the debug x25 annexg command:

X.25-2# debug x25 annexg
   X.25 over FR (Annex-G) debugging is on
   X.25-2#
   02:16:54: annexg_restart_tx: sending pak to Serial0
   02:16:54: annexg_restart_tx: sending pak to Serial0
   02:16:54: annexg_restart_tx: sending pak to Serial0
   02:16:54: annexg_restart_tx: sending pak to Serial0

Troubleshooting Example

Given below is an example of troubleshooting using the various commands listed above.

The pad command is used to log on to a remote X.25 router, similar to using the telnet command in a TCP/IP network.

The debug x25 events outputs, shown in sequential order below, are displayed when a pad call is placed from X.25-4 to X.25-1.

X.25-r4# debug x25 events
X.25 special event debugging is on

X.25-r4# pad 1234

!--- Make a pad call from X.25-4 to X.25-1.

Trying 1234...Open

   User Access Verification

Password:
   01:48:44: Serial0: X.25 O R1 Call (13) 8 lci 1
   01:48:44: From (4): 4321 To (4): 1234
   01:48:44: Facilities: (0)
   01:48:44: Call User Data (4): 0x01000000 (pad)
   01:48:44: Serial0: X.25 I R1 Call Confirm (3) 8 lci 1
   X.25-1>

x.25-r4# show x25 context
Serial0
  X.25 DCE, address 4321, state R1, modulo 8, timer 0
      Defaults: idle VC timeout 0
        cisco encapsulation
        input/output window sizes 2/2, packet sizes 128/128
      Timers: T10 60, T11 180, T12 60, T13 60
      Channels: Incoming-only none, Two-way 1-1024, Outgoing-only none
      RESTARTs 2/0 CALLs 9+3/2+0/0+0 DIAGs 0/0
  LAPB DCE, state CONNECT, modulo 8, k 7, N1 12056, N2 20
      T1 3000, T2 0, interface outage (partial T3) 0, T4 0
      VS 0, VR 2, tx NR 2, Remote VR 0, Retransmissions 0
      Queues: U/S frames 0, I frames 0, unack. 0, reTx 0
      IFRAMEs 504/594 RNRs 0/0 REJs 0/0 SABM/Es 2/0 FRMRs 0/0 DISCs 0/0

x.25-r4# show x25 vc
SVC 1024,  State: D1,  Interface: Serial0
  Started 01:06:07, last input 00:06:18, output 00:06:18
  Connects 1234 <-> ip 10.0.0.2
  Call PID ietf, Data PID none
  Window size input: 2, output: 2
  Packet size input: 128, output: 128
  PS: 1  PR: 2  ACK: 2  Remote PR: 0  RCNT: 0  RNR: no
  P/D state timeouts: 0  timer (secs): 0
  data bytes 2500/2950 packets 25/34 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0

!--- The following call passes through X.25-3:

X.25-3# debug x25 events
X.25 special event debugging is on
X.25-3#
01:36:28: Serial0: X.25 I R1 Call (13) 8 lci 1
01:36:28:   From (4): 4321 To (4): 1234
01:36:28:   Facilities: (0)
01:36:28:   Call User Data (4): 0x01000000 (pad)
01:36:28: Se1 DLCI 110: X.25 O R1 Call (16) 8 lci 1
01:36:28:   From (4): 4321 To (4): 1234
01:36:28:   Facilities: (3)
01:36:28:     Window sizes: 2 2
01:36:28:   Call User Data (4): 0x01000000 (pad)
01:36:28: Se1 DLCI 110: X.25 I R1 Call Confirm (8) 8 lci 1

X.25-3# show x25 context
Serial0
  X.25 DTE, address <none>, state R1, modulo 8, timer 0
      Defaults: idle VC timeout 0
        cisco encapsulation
        input/output window sizes 2/2, packet sizes 128/128
      Timers: T20 180, T21 200, T22 180, T23 180
      Channels: Incoming-only none, Two-way 1-1024, Outgoing-only none
      RESTARTs 1/1 CALLs 2+0/9+3/9+0 DIAGs 0/0
  LAPB DTE, state CONNECT, modulo 8, k 7, N1 12056, N2 20
      T1 3000, T2 0, interface outage (partial T3) 0, T4 0
      VS 2, VR 0, tx NR 0, Remote VR 2, Retransmissions 0
      Queues: U/S frames 0, I frames 0, unack. 0, reTx 0
      IFRAMEs 594/504 RNRs 0/0 REJs 0/0 SABM/Es 2/1 FRMRs 0/0 DISCs 0/0
Serial1 DLCI 110
  PROFILE DCE, address 2222, state R1, modulo 8, timer 0
      Defaults: idle VC timeout 0
        input/output window sizes 7/7, packet sizes 128/128
      Timers: T10 60, T11 180, T12 60, T13 60
      Channels: Incoming-only none, Two-way 1-1024, Outgoing-only none
      RESTARTs 1/0 CALLs 9+0/2+0/2+0 DIAGs 0/0
  LAPB DCE, state CONNECT, modulo 8, k 7, N1 12056, N2 20
      T1 3200, T2 0, interface outage (partial T3) 0, T4 0
      VS 2, VR 7, tx NR 7, Remote VR 2, Retransmissions 0
      Queues: U/S frames 0, I frames 0, unack. 0, reTx 0
      IFRAMEs 498/591 RNRs 0/0 REJs 0/0 SABM/Es 1/0 FRMRs 0/0 DISCs 0/0
XOT
  address <none>, state R/Inactive, modulo 8
      Defaults: idle VC timeout 0
        input/output window sizes 2/2, packet sizes 128/128
      Timers: T20 180, T21 200, T22 180, T23 180

X.25-3# show x25 vc
SVC 1024,  State: D1,  Interface: Serial0
  Started 01:05:37, last input 00:05:49, output 00:05:49
  Connects 1234 <--> 4321 from Serial1 DLCI 110
  Window size input: 2, output: 2
  Packet size input: 128, output: 128
  PS: 2  PR: 1  ACK: 0  Remote PR: 2  RCNT: 1  RNR: no
  P/D state timeouts: 0  timer (secs): 0
  data bytes 2950/2500 packets 34/25 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0
SVC 1024,  State: D1,  Interface: Se1 DLCI 110
  Started 01:05:37, last input 00:05:49, output 00:05:49
  Connects 1234 <--> 4321 to Serial0 SVC 1024
  Window size input: 2, output: 2
  Packet size input: 128, output: 128
  PS: 1  PR: 2  ACK: 2  Remote PR: 0  RCNT: 0  RNR: no
  P/D state timeouts: 0  timer (secs): 0
  data bytes 2500/2950 packets 25/34 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0

!--- X.25-2 receives the call from X.25-3 through 
!--- Frame Relay and then passes it to X.25-1.

X.25-2# debug x25 events
X.25 special event debugging is on
X.25-2#
02:07:50: Se0 DLCI 100: X.25 I R1 Call (16) 8 lci 1
02:07:50:   From (4): 4321 To (4): 1234
02:07:50:   Facilities: (3)
02:07:50:     Window sizes: 2 2
02:07:50:   Call User Data (4): 0x01000000 (pad)
02:07:50: Serial1: X.25 O R1 Call (13) 8 lci 1
02:07:50:   From (4): 4321 To (4): 1234
02:07:50:   Facilities: (0)
02:07:50:   Call User Data (4): 0x01000000 (pad)
02:07:50: Serial1: X.25 I R1 Call Confirm (3) 8 lci 1
02:07:50: Se0 DLCI 100: X.25 O R1 Call Confirm (8) 8 lci 1

X.25-2# show x25 vc
SVC 1024,  State: D1,  Interface: Se0 DLCI 100
  Started 01:04:43, last input 00:04:55, output 00:04:55
  Connects 1234 <--> 4321 from Serial1 SVC 1024
  Window size input: 2, output: 2
  Packet size input: 128, output: 128
  PS: 2  PR: 1  ACK: 0  Remote PR: 2  RCNT: 1  RNR: no
  P/D state timeouts: 0  timer (secs): 0
  data bytes 2950/2500 packets 34/25 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0
SVC 1024,  State: D1,  Interface: Serial1
  Started 01:04:44, last input 00:04:55, output 00:04:55
  Connects 1234 <--> 4321 to Serial0 DLCI 100
  Window size input: 2, output: 2
  Packet size input: 128, output: 128
  PS: 1  PR: 2  ACK: 2  Remote PR: 0  RCNT: 0  RNR: no
  P/D state timeouts: 0  timer (secs): 0
  data bytes 2500/2950 packets 25/34 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0

!--- X.25-1 receives the call and connects it to the vty port.

X.25-1# debug x25 events
X.25 special event debugging is on
X.25-1#
03:58:00: Serial0: X.25 O R1 Call (13) 8 lci 1023
03:58:00:   From (4): 1234 To (4): 1234
03:58:00:   Facilities: (0)
03:58:00:   Call User Data (4): 0x01000000 (pad)
03:58:00: Serial0: X.25 I R1 Clear (5) 8 lci 1023
03:58:00:   Cause 13, Diag 64 (Not obtainable/Call or Clear problem)
03:58:00: Serial0: X.25 O R1 Clear Confirm (3) 8 lci 1023
X.25-1#

X.25-1# show x25 vc
   SVC 1024, State: D1, Interface: Serial0
   Started 01:04:11, last input 00:04:22, output 00:04:23
   Connects 4321 <-> ip 10.0.0.1
   Call PID cisco, Data PID none
   Window size input: 2, output: 2
   Packet size input: 128, output: 128
   PS: 2 PR: 1 ACK: 0 Remote PR: 2 RCNT: 1 RNR: no
   P/D state timeouts: 0 timer (secs): 0
   data bytes 2950/2500 packets 34/25 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0

Similarly, you can transport X.25 frames over TCP; such transport is known as XOT and can be sent over a Frame Relay network. For more details, refer X.25 Over Frame Relay with TCP Configured (XOT).

Related Information

• Annex G (X.25 over Frame Relay)
• X.25 Back-to-Back Connections
• X.25 Background
• Internetworking Design Basics
• DNS Based X.25 Routing
• Configuring X.25 and LAPB
• Cisco IOS Wide-Area Networking Command Reference
• X.25 Technical Support Page
• Technical Support - Cisco Systems