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X.25 Protocols

Transporting X.25 over Frame Relay with XOT

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Document ID: 12502


Contents

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

Introduction

This document illustrates how to transport X.25 frames over Frame Relay with TCP configured. 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. This document uses Frame Relay as the Layer 2 technology configured with TCP. X.25 Over TCP (XOT) enables you to transport X.25 packets over a TCP/IP network instead of a Link Access Procedure, Balanced (LAPB) link. It allows you to tunnel X.25 traffic through an IP network.

Note: You can also transport X.25 frames directly over Frame Relay without configuring TCP. This is known as Annex G. With Annex G, the process of transporting X.25 over Frame Relay is simpler, allowing direct X.25 encapsulation over a Frame Relay network. For more details, refer to Annex G (X.25 over Frame Relay).

Prerequisites

Requirements

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

  • A basic understanding of X.25

  • A basic understanding of Frame Relay

Components Used

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

  • Cisco 2500 routers

  • Cisco IOS® Software Release 12.2(10b)

Note: For Cisco IOS Software versions earlier than 11.3, the format of the x25 route ^xxxx xot a.b.c.d command should be x25 route ^xxxx ip a.b.c.d.

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, 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.

Note: Use the Command Lookup Tool (registered customers only) to find more information on the commands used in this document.

Network Diagram

This document uses this network setup:

x25_over_frame_w_tcp.gif

Configurations

This document uses these configurations.

X.25-1

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

!--- Specifies the operation of a serial interface as an X.25 device.
!--- Default x.25 encapsulation mode is "dte."

 bandwidth 64 
 x25 address 1234 

!--- Sets the X.121 address.
 
 x25 map ip 10.0.0.1 4321 broadcast 

!--- Sets up the LAN protocols-to-remote host mapping. The keyword
!--- "broadcast" causes the Cisco IOS software to direct any broadcasts 
!--- sent through this interface to the specified X.121 address.


!

X.25-2

 
version 12.2
!
x25 routing

!--- Enables X.25 local switching.


! 
service tcp-keepalives-in 
service tcp-keepalives-out 

!--- Enables XOT keepalives so that, if the TCP underlayer is 
!--- broken, x25 can detect the problem and take action, rather 
!--- than rely on TCP itself to detect and take action eventually.


! 
interface Serial0 
 no ip address 
 encapsulation frame-relay IETF 

!--- Enables 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 

!--- Configures an interface for the ANSI Annex D Local Management
!--- Interface (LMI) type.

! 
interface Serial0.1 point-to-point 
 ip address 192.168.1.1 255.255.255.0 
 frame-relay interface-dlci 100 

!--- Assigns a data-link connection identifier (DLCI) to a specified 
!--- Frame Relay subinterface on the router.
 
! 
interface Serial1 
 no ip address 
 no ip mroute-cache 
 encapsulation x25 dce 

!--- Specifies the operation of a serial interface as an X.25 DCE device.
 
 bandwidth 64 
 clock rate 64000 
! 
x25 route ^1234 interface Serial1 

!--- Specifies that any call with a destination address beginning with
!--- 1234 that is received on an interface other than serial 1
!---  is forwarded to serial 1.
 
x25 route ^4321 xot 192.168.1.2

!--- Routes the call to the XOT host at the specified IP address.
!--- The disposition keyword "xot" is new. In earlier releases, 
!--- the keyword "ip" was used.

 
!

X.25-3

 
version 12.2
!
x25 routing
! 
service tcp-keepalives-in 
service tcp-keepalives-out 
! 
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 
! 
interface Serial1.1 point-to-point 
 ip address 192.168.1.2 255.255.255.0 
 frame-relay interface-dlci 110 
! 
x25 route ^4321 interface Serial0 

!--- Specifies that any call with a destination address beginning 
!--- with 4321 that is received on an interface other than serial 
!--- 0 is forwarded to serial 0.

x25 route ^1234 xot 192.168.1.1 
!

X.25-4

 
version 12.2
!
ip subnet-zero
! 
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 you can use to confirm that your configuration works properly.

The Output Interpreter Tool (registered customers only) (OIT) supports certain show commands. Use the OIT to view an analysis of show command output.

  • ping—Checks host accessibility and network connectivity.

  • pad—Use this command to log on to a packet assembler/disassembler (PAD). Refer to the Command Reference for more details.

  • show x25 xot—Displays information for all XOT virtual circuits. Refer to the Wide-Area Networking Command Reference for more details.

  • show tcp—Displays the status of TCP connections and the TCP connection parameters.

  • show x25 context—Displays operating configuration status details of an Annex G DLCI link. Refer to the Wide-Area Networking Command Reference for more details.

The following is an example output of the ping command:

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 = 156/160/172 ms

Troubleshoot

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

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: Refer to Important Information on Debug Commands before you use debug commands.

  • debug X25 events—Shows X.25 traffic without normal data and relative rate (RR) packets.

  • debug ip tcp driver—Displays TCP Driver events.

  • show x25 xot—Displays information for all XOT virtual circuits.

  • show tcp—Displays the status of TCP connections and the TCP connection parameters.

  • show x25 context—Displays operating configuration status details of an Annex G DLCI link. Refer to the Wide-Area Networking Command Reference for more details.

  • clear x25—Restarts an X.25 service.

The usage of these troubleshooting commands is shown below. The following is the output of the debug x25 events command when a PAD call is placed from X.25-4 to X.25-1:

X.25-4# debug x25 events
   X.25 special event debugging is on

Below, a PAD call is made from X.25-4 to X.25-1.

X.25-4# pad 1234
   Trying 1234...Open 

   User Access Verification
Password:
   06:32:44: Serial0: X.25 O R1 Call (13) 8 lci 2
   06:32:44: From (4): 4321 To (4): 1234
   06:32:44: Facilities: (0)
   06:32:44: Call User Data (4): 0x01000000 (pad)
   06:32:44: Serial0: X.25 I R1 Call Confirm (3) 8 lci 2
 

X.25-4# 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 3/0 CALLs 8+1/0+1/0+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 3, tx NR 3, Remote VR 0, Retransmissions 0
   Queues: U/S frames 0, I frames 0, unack. 0, reTx 0
   IFRAMEs 7370/4357 RNRs 0/0 REJs 0/0 SABM/Es 4/0 FRMRs 0/0 DISCs 0/0

The following call passes through X.25-3:

X.25-3# debug x25 events
   X.25 special event debugging is on
   R3#
   06:30:58: Serial0: X.25 I R1 Call (13) 8 lci 2
   06:30:58: From (4): 4321 To (4): 1234
   06:30:58: Facilities: (0)
   06:30:58: Call User Data (4): 0x01000000 (pad)
   06:30:58: [192.168.1.1,1998/192.168.1.2,11006]: 
   XOT O P2 Call (19) 8 lci 1
   06:30:58: From (4): 4321 To (4): 1234
   06:30:58: Facilities: (6)
   06:30:58: Packet sizes: 128 128
   06:30:58: Window sizes: 2 2
   06:30:58: Call User Data (4): 0x01000000 (pad)
   06:30:58: [192.168.1.1,1998/192.168.1.2,11006]: 
   XOT I P2 Call Confirm (11) 8 lci 1
   06:30:58: From (0): To (0):
   06:30:58: Facilities: (6)
   06:30:58: Packet sizes: 128 128
   06:30:58: Window sizes: 2 2
   06:30:58: Serial0: X.25 O R1 Call Confirm (3) 8 lci 2
 
X.25-3# show x25 xot
   SVC 1, State: D1, Interface: [192.168.1.1,1998/192.168.1.2,11004]
   Started 02:33:26, last input 02:18:01, output 02:18:01
   Connects 4321 <--> 1234 from Serial0 SVC 1
   Window size input: 2, output: 2
   Packet size input: 128, output: 128
   PS: 7 PR: 7 ACK: 7 Remote PR: 6 RCNT: 0 RNR: no
   P/D state timeouts: 0 timer (secs): 0
   data bytes 1500/1500 packets 15/15 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0 

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 3/0 CALLs 0+1/8+1/8+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 3, VR 0, tx NR 0, Remote VR 3, Retransmissions 0
   Queues: U/S frames 0, I frames 0, unack. 0, reTx 0
   IFRAMEs 4357/7370 RNRs 0/0 REJs 0/0 SABM/Es 216/3 FRMRs 0/0 DISCs 0/0
   XOT
   address <none>, state R1, 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
   RESTARTs 0/0 CALLs 8+0/0+0/0+0 DIAGs 0/0

Below, 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#
20:52:00: [192.168.1.2,11008/192.168.1.1,1998]:
XOT I P/Inactive Call (19) 8 lci 1
20:52:00:   From (4): 4321 To (4): 1234
20:52:00:   Facilities: (6)
20:52:00:     Packet sizes: 128 128
20:52:00:     Window sizes: 2 2
20:52:00:   Call User Data (4): 0x01000000 (pad)
20:52:00: Serial1: X.25 O R1 Call (13) 8 lci 2
20:52:00:   From (4): 4321 To (4): 1234
20:52:00:   Facilities: (0)
20:52:00:   Call User Data (4): 0x01000000 (pad)
20:52:00: Serial1: X.25 I R1 Call Confirm (3) 8 lci 2
20:52:00: [192.168.1.2,11008/192.168.1.1,1998]: 
XOT O P3 Call Confirm (11) 8 lci 1
20:52:00:   From (0):  To (0):
20:52:00:   Facilities: (6)
20:52:00:     Packet sizes: 128 128
20:52:00:     Window sizes: 2 2 

X.25-2# show tcp

Stand-alone TCP connection from host 192.168.1.2
   Connection state is ESTAB, I/O status: 1, unread input bytes: 0
   Local host: 192.168.1.1, Local port: 1998
   Foreign host: 192.168.1.2, Foreign port: 11004

Enqueued packets for retransmit: 0, input: 0 mis-ordered: 0 (0 bytes)

TCP driver queue size 0, flow controlled FALSE

Event Timers (current time is 0x17006CC):
   Timer Starts Wakeups Next
   Retrans 12 0 0x0
   TimeWait 0 0 0x0
   AckHold 11 0 0x0
   SendWnd 0 0 0x0
   KeepAlive 59 0 0x170EB64
   GiveUp 0 0 0x0
   PmtuAger 0 0 0x0
   DeadWait 0 0 0x0

iss: 4214401864 snduna: 4214402950 sndnxt: 4214402950 sndwnd: 7107
   irs: 1070266017 rcvnxt: 1070267111 rcvwnd: 7099 delrcvwnd: 1093

SRTT: 239 ms, RTTO: 712 ms, RTV: 473 ms, KRTT: 0 ms
   minRTT: 32 ms, maxRTT: 300 ms, ACK hold: 200 ms
   Flags: passive open, retransmission timeout, keepalive running
   gen tcbs

Datagrams (max data segment is 1460 bytes):
   Rcvd: 49 (out of order: 0), with data: 11, total data bytes: 1093
   Sent: 48 (retransmit: 0, fastretransmit: 0), with data: 11, 
   total data bytes:    1085

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

X.25-1# debug x25 events
	X.25-1#
   21:08:05: Serial0: X.25 I R1 Call (13) 8 lci 2
   21:08:05: From (4): 4321 To (4): 1234
   21:08:05: Facilities: (0)
   21:08:05: Call User Data (4): 0x01000000 (pad)
   21:08:05: Serial0: X.25 O R1 Call Confirm (3) 8 lci 2 

X.25-1# show x25 vc
   SVC 1, State: D1, Interface: Serial0
   Started 00:14:54, last input 00:14:35, output 00:14:35
   Connects 4321 <-> ip 10.0.0.1
   Call PID ietf, Data PID none
   Window size input: 2, output: 2
   Packet size input: 128, output: 128
   PS: 2 PR: 2 ACK: 2 Remote PR: 1 RCNT: 0 RNR: no
   P/D state timeouts: 0 timer (secs): 0
   data bytes 1000/1000 packets 10/10 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0

Related Information

Updated: Jun 01, 2005 Document ID: 12502