X.25 Protocols

Document ID: 14217

Contents

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

Introduction

This document presents a configuration example in which a Cisco router switches X.25 traffic between two X.25 data terminal equipment (DTE) devices with both different window sizes and different packet sizes.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

The router that plays the role of an X.25 switch with asymmetrical windows and packets must run Cisco IOS® Software Release 12.0(7)T or later. No restrictions are imposed on the IOS versions of the two routers that play the role of X.25 DTE devices in this configuration example.

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 Cisco Technical Tips Conventions.

Background Information

X.25 asymmetrical windows and packets is a new feature that was introduced in Cisco IOS Software release 12.0(7)T. It allows connectivity between devices that have different window sizes and packet sizes.

For example, this feature can be useful when you have to interconnect an X.25 device that uses some window sizes (and packet sizes) that differ from those used by the X.25 service provider. This is shown in a simple line diagram:

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 this network setup:

Note: The routers called Router 1 and Router 2 have different window and packet sizes in their shared link.

Note: Note that the two X.25 DTE devices (Router 1 and Router 3) have different window and packet sizes in their respective X.25 interfaces. Despite this difference, they are able to communicate due to the fact that we have configured the router acting as X.25 switch (Router 2) to disable flow control parameter negotiation (using the X.25 subscribe flow-control never command).

Configurations

This document uses these configurations:

Note: These configurations are truncated to display the relevant information.

router1#show run
version 12.0
service pad to-xot
service pad from-xot
service pad cmns
service timestamps debug datetime msec
service timestamps log datetime msec

hostname router1

x25 routing


interface Serial0
 description description ### DCE port to router3, serial 4/2 ###
 ip address 9.0.0.2 255.255.255.252
 no ip directed-broadcast
 no fair-queue
 clockrate 2000000
 no cdp enable
!
interface Serial1
 description ### V.35 DTE, serial line to router2 serial 0 ###
 ip address 7.0.0.2 255.255.255.0
 no ip directed-broadcast
 encapsulation x25
 no ip mroute-cache
 x25 address 111
 x25 win 5
 x25 wout 5
 x25 ips 256
 x25 ops 512
 no cdp enable
!

router2#show run

version 12.1

service timestamps debug datetime msec
service timestamps log datetime msec
!
hostname router2
!
x25 routing acknowledge local
cns event-service server

interface Serial0
 description ### V.35 DCE, serial line to router1 serial 1 ###
 ip address 7.0.0.1 255.255.255.0
 encapsulation x25 dce
 x25 address 222
 x25 ips 512
 x25 ops 256
 x25 subscribe flow-control never
 clockrate 64000
 no cdp enable
!
interface Serial1
 description ### DTE port to router3, serial 4/2 #####
 ip address 12.0.0.1 255.255.255.0
 encapsulation x25 dce
 x25 subscribe flow-control never
 ignore-dcd
 no cdp enable
!

x25 route 444 interface Serial1
x25 route 111 interface Serial0

router3#show run interface serial4/2

interface Serial4/2
 description *** static DCE connection to s1 router2
 ip address 12.0.0.2 255.255.255.0
 encapsulation x25
 no ip mroute-cache
 tx-queue-limit 6
 x25 address 444
 clockrate 2000000
!

Verify

There is currently no verification procedure available for this configuration.

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: Before issuing debug commands, refer to Important Information on Debug Commands.

• show debug—Displays the debug commands that are enabled.

• show interface s0—Views the status of the s0 interface.

From Router 1, we initiate a pad 444 command in order to force an outgoing X.25 call to Router 3. This call is switched by Router 2.

The debugs collected from Router 2 are as follows:

router 2#show debug
X.25:
X.25 packet debugging is on
Mar 9 01:54:01.955: Serial0: X.25 I R1 Call (12) 
8 lci 1024Mar 9 01:54:01.959: From (3): 111 To (3): 444
Mar 9 01:54:01.963: Facilities: (0)
Mar 9 01:54:01.963: Call User Data (4): 0x01000000 (pad) 
Mar 9 01:54:01.971: Serial1: X.25 O R1 Call (12) 8 lci 1
Mar 9 01:54:01.975: From (3): 111 To (3): 444 
Mar 9 01:54:01.979: Facilities: (0) 
Mar 9 01:54:01.979: Call User Data (4): 0x01000000 (pad) 
Mar 9 01:54:01.987: Serial1: X.25 I R1 Call Confirm (5) 8 lci 1 
Mar 9 01:54:01.991: From (0): To (0): 
Mar 9 01:54:01.991: Facilities: (0) 
Mar 9 01:54:01.995: Serial0: X.25 O R1 Call Confirm (5) 8 lci 1024 
Mar 9 01:54:01.995: From (0): To (0): 
Mar 9 01:54:01.999: Facilities: (0) 
Mar 9 01:54:02.003: Serial1: X.25 I D1 Data (4) Q 8 lci 1 PS 0 PR 0 
Mar 9 01:54:02.007: Serial1: X.25 I D1 Data (45) 8 lci 1 PS 1 PR 0 
Mar 9 01:54:02.011: Serial1: X.25 O D1 RR (3) 8 lci 1 PR 2      
Mar 9 01:54:02.015: Serial0: X.25 O D1 Data (4) Q 8 lci 1024 PS 0 PR 0 
Mar 9 01:54:02.019: Serial0: X.25 O D1 Data (45) 8 lci 1024 PS 1 PR 0 
Mar 9 01:54:02.027: Serial0: X.25 I D1 Data (48) Q 8 lci 1024 PS 0 PR 0 
Mar 9 01:54:02.031: Serial1: X.25 O D1 Data (48) Q 8 lci 1 PS 0 PR 2 
Mar 9 01:54:02.035: Serial0: X.25 I D1 RR (3) 8 lci 1024 PR 1 
Mar 9 01:54:02.039: Serial0: X.25 I D1 RR (3) 8 lci 1024 PR 2 
Mar 9 01:54:02.043: Serial1: X.25 I D1 Data (12) Q 8 lci 1 PS 2 PR 0 
Mar 9 01:54:02.047: Serial0: X.25 O D1 Data (12) Q 8 lci 1024 PS 2 PR 1 
Mar 9 01:54:02.051: Serial1: X.25 I D1 RR (3) 8 lci 1 PR 1 
Mar 9 01:54:02.059: Serial0: X.25 I D1 Data (12) Q 8 lci 1024 PS 1 PR 2 
Mar 9 01:54:02.063: Serial1: X.25 O D1 Data (12) Q 8 lci 1 PS 1 PR 3 
Mar 9 01:54:02.067: Serial0: X.25 I D1 RR (3) 8 lci 1024 PR 3 
Mar 9 01:54:02.067: Serial1: X.25 I D1 RR (3) 8 lci 1 PR 2 
Mar 9 01:54:14.399: Serial0: X.25 I D1 Data (4) 8 lci 1024 PS 2 PR 3 
Mar 9 01:54:14.403: Serial1: X.25 O D1 Data (4) 8 lci 1 PS 2 PR 3 
Mar 9 01:54:14.407: Serial0: X.25 O D1 RR (3) 8 lci 1024 PR 3 
Mar 9 01:54:14.411: Serial1: X.25 I D1 RR (3) 8 lci 1 PR 3 
Mar 9 01:54:14.699: Serial0: X.25 I D1 Data (4) 8 lci 1024 PS 3 PR 3 
Mar 9 01:54:14.703: Serial1: X.25 O D1 Data (4) 8 lci 1 PS 3 PR 3 
Mar 9 01:54:14.707: Serial1: X.25 I D1 RR (3) 8 lci 1 PR 4 
Mar 9 01:54:16.635: Serial0: X.25 I D1 Data (4) 8 lci 1024 PS 4 PR 3 
Mar 9 01:54:16.639: Serial1: X.25 O D1 Data (4) 8 lci 1 PS 4 PR 3 
Mar 9 01:54:16.643: Serial0: X.25 O D1 RR (3) 8 lci 1024 PR 5 
Mar 9 01:54:16.647: Serial1: X.25 I D1 RR (3) 8 lci 1 PR 5 
Mar 9 01:54:16.651: Serial1: X.25 I D1 Data (131) 8 lci 1 M PS 3 PR 5 
Mar 9 01:54:16.655: Serial1: X.25 I D1 Data (131) 8 lci 1 M PS 4 PR 5 
Mar 9 01:54:16.659: Serial0: X.25 O D1 Data (259) 8 lci 1024 M PS 3 PR 5
Mar 9 01:54:16.663: Serial1: X.25 O D1 RR (3) 8 lci 1 PR 5
Mar 9 01:54:16.667: Serial1: X.25 I D1 Data (131) 8 lci 1 M PS 5 PR 5 
Mar 9 01:54:16.671: Serial1: X.25 I D1 Data (131) 8 lci 1 M PS 6 PR 5 
Mar 9 01:54:16.675: Serial1: X.25 O D1 RR (3) 8 lci 1 PR 7 
Mar 9 01:54:16.683: Serial1: X.25 I D1 Data (131) 8 lci 1 M PS 7 PR 5 
Mar 9 01:54:16.687: Serial1: X.25 I D1 Data (131) 8 lci 1 M PS 0 PR 5 
Mar 9 01:54:16.691: Serial1: X.25 O D1 RR (3) 8 lci 1 PR 1 
Mar 9 01:54:16.695: Serial0: X.25 O D1 Data (259) 8 lci 1024 M PS 4 PR 5

Note: The two last packets with 131 bytes each (received through interface Serial 1) have been assembled into one single packet of 259 bytes (shown in bold above) sent out through interface Serial 0 . This is because x25 subscribe flow-control never is configured in interface Serial 0.

router 2#show interface s0 
Serial0 is up, line protocol is up 
Hardware is HD64570 
Description: ### V.35 DCE, serial line to router 1 serial 1 ### 
Internet address is 7.0.0.1/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, reliability 255/255, 
txload 1/255, rxload 1/255 
Encapsulation X25, loopback not set X.25 DCE, address 222, 
state R1, modulo 8, timer 0 
Defaults: idle VC timeout 0 cisco encapsulation input/output window sizes 2/2, 
packet sizes 512/256 
Flow control negotiation is disabled.

Related Information

• X.25 Switch Local Acknowledgment
• X.25 Technical Tips
• Technical Support - Cisco Systems