Cisco CCIE: X.25 to TCP Translation

In preparation of our CCNP exam, we want to make sure we cover the various concepts that we could see on our Cisco CCNP exam. So to assist you, below we will discuss X.25 to TCP Translation.

Introduction

XOT (X.25 Over TCP) is designed by Cisco Systems, and is detailed in Request For Comments (RFC) 1613, to transport X.25 over IP internets. This allows X.25 packets to be sent over a Transmission Control Protocol/Internet Protocol (TCP/IP) network instead of a Link Access Procedure, Balanced (LAPB) link.

XOT is a method of sending X.25 packets over IP internets through encapsulation of the X.25 Packet Level in TCP packets.

This document presents a sample configuration that illustrates these two translations:

Transmission Control Protocol (TCP) to X.25 translation.

X.25 to TCP translation.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

This translation requires the ENTERPRISE feature set, which is only supported on Cisco router platforms 26xx and above.

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.

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:

As shown here, back-to-back links are used between Routers 1 and 2 and between Routers 2 and 3.

Configurations

This document uses these configurations:

Router1

Router2

Router3

Note: We have truncated the following configurations to display the relevant information.

Verify

Use the following commands to test 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.

show debugenables you to display a variety of debug information, or to perform specific troubleshooting activities.

telnet 192.168.7.2connects to computer systems on the Internet in prompt mode. ·
pad 345logs you on to a PAD.

show x25 vcdisplays information about active switched virtual circuits (SVCs), and permanent virtual circuits (PVCs) in privileged EXEC mode.

The output shown in the tests below is a result of entering these commands on the devices shown in the network diagram above. This output shows that the network is operating properly.

Test 1: TCP to X.25 Translation

In this test, we perform a Telnet session from Router1 to the IP address of Router2:

Telnet 192.168.7.2 from Router1.

Note: This address belongs to the network 192.168.7.0 /24 in Router2. This address must not be assigned to any other system in the network.

Router2 does a TCP to X.25 translation in order to reach Router3. The output is shown below.

     Router2#show debug

     TCP:
     TCP special event debugging is on
     X.29 PAD:
     X25 PAD debugging is on
     X.25:
     X.25 special event debugging is on
     Protocol translation:
     Protocol Translation debugging is on

     Router2#
     Router1#telnet 192.168.7.2
     Trying 192.168.7.2 ... Open
     Trying 123...Open
     User Access Verification
     Password:
     Router3>
     Router2#
     *Mar 1 01:50:28.759: TCP0: state was LISTEN -> SYNRCVD [23 -> 10.0.0.6(11007)]
     *Mar 1 01:50:28.763: TCB00499CAC setting property TCP_TOS (11) C0094
     *Mar 1 01:50:28.767: tcppad2: fork started
     *Mar 1 01:50:28.767: TCP: sending SYN, seq 3338770911, ack 4026886977
     *Mar 1 01:50:28.771: TCP2: Connection to 10.0.0.6:11007, advertising MSS 1460
     *Mar 1 01:50:28.775: TCP2: Connection to 10.0.0.6:11007, received MSS 556, MSS is 556
     *Mar 1 01:50:28.791: TCP2: state was SYNRCVD -> ESTAB [23 -> 10.0.0.6(11007)]
     *Mar 1 01:50:28.803: pad_open_connection: found a valid route
     *Mar 1 01:50:28.807: Serial0: X.25 O R1 Call (11) 8 lci 1
     *Mar 1 01:50:28.811: From (0): To (3): 123
     *Mar 1 01:50:28.811: Facilities: (0)
     *Mar 1 01:50:28.815: Call User Data (4): 0x01000000 (pad)
     *Mar 1 01:50:28.827: Serial0: X.25 I R1 Call Confirm (5) 8 lci 1
     *Mar 1 01:50:28.831: From (0): To (0):
     *Mar 1 01:50:28.835: Facilities: (0)
     *Mar 1 01:50:28.835: PAD2: Call completed
     *Mar 1 01:50:28.839: PAD2: Control packet received.
     *Mar 1 01:50:28.851: PAD2: Input X29 packet type 4 (Read X.3 param) len 1
     *Mar 1 01:50:28.855: PAD2: Output X29 packet type 0 (Parameter indication) len 45

     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,
     *Mar 1 01:50:28.879: PAD2: Control packet received.
     *Mar 1 01:50:28.883: PAD2: Input X29 packet type 6 (Set and Read) len 9
     2:0, 4:1, 15:0, 7:21,
     Mar 1 01:50:28.887: tcppad2: Sending WILL ECHO
     Mar 1 01:50:28.891: PAD2: Output X29 packet type 0 (Parameter indication)len9

     2:0, 4:1, 15:0, 7:21,
     Router2#show x25 vc
     SVC 1, State: D1, Interface: Serial0
     Started 00:00:25, last input 00:00:22, output 00:00:22
     Line: 2 vty 0 Location: Host: 10.0.0.6
     connected to 123 PAD <--> X25
     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 57/62 packets 5/4 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0
     Router2#

Test 2: X.25 to TCP translation

In this test, we start a packet assembler/disassembler (PAD) session from Router3 to the X.25 address of Router2:

  Do a PAD to 345 from Router3. 1.
     Router2 does an X.25 to TCP translation in order to reach Router1. The output is shown below. 2.
     Router2#show debug
     TCP:
     TCP special event debugging is on
     X.29 PAD:
     X25 PAD debugging is on
     X.25:
     X.25 special event debugging is on
     Protocol translation:
     Protocol Translation debugging is on
     Router2#
     Router3#pad 345
     Trying 345...Open
     Trying 10.0.0.6 ... Open
     User Access Verification
     Password: CCCC
     Router1>
     Router2#
     *Mar 1 01:51:31.475: Serial0: X.25 I R1 Call (12) 8 lci 1024
     *Mar 1 01:51:31.479: From (3): 123 To (3): 345
     *Mar 1 01:51:31.483: Facilities: (0)
     *Mar 1 01:51:31.483: Call User Data (4): 0x01000000 (pad)
     *Mar 1 01:51:31.487: PAD: translate call to 345
     *Mar 1 01:51:31.491: Call User Data (4): 0x01000000 (pad)
     *Mar 1 01:51:31.495: PAD: Creating proto translation on tty2 for vc 1024
     *Mar 1 01:51:31.499: Serial0: X.25 O R1 Call Confirm (5) 8 lci 1024
     *Mar 1 01:51:31.503: From (0): To (0):
     *Mar 1 01:51:31.503: Facilities: (0)
     *Mar 1 01:51:31.507: PAD2: Call completed
     *Mar 1 01:51:31.511: padtcp2: fork started
     *Mar 1 01:51:31.515: PAD2: Output X29 packet type 4 (Read X.3 param) len 1
     *Mar 1 01:51:31.523: TCB0049E7A4 created
     *Mar 1 01:51:31.523: TCB0049E7A4 setting property TCP_TOS (11) 49C853
     *Mar 1 01:51:31.527: TCB0049E7A4 bound to UNKNOWN.44034
     *Mar 1 01:51:31.531: PAD2: Control packet received.
     *Mar 1 01:51:31.531: TCP: sending SYN, seq 3401534831, ack 0
     *Mar 1 01:51:31.535: TCP2: Connection to 10.0.0.6:23, advertising MSS 1460
     *Mar 1 01:51:31.539: TCP2: state was CLOSED -> SYNSENT [44034 -> 10.0.0.6(23)]
     *Mar 1 01:51:31.559: TCP2: state was SYNSENT -> ESTAB [44034 -> 10.0.0.6(23)]
     *Mar 1 01:51:31.563: TCP2: Connection to 10.0.0.6:23, received MSS 1460, MSS is 1460
     *Mar 1 01:51:31.567: TCB0049E7A4 connected to 10.0.0.6.23
     *Mar 1 01:51:31.571: PAD2: Input X29 packet type 0 (Parameter indication) len 45

     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,
     *Mar 1 01:51:31.583: PAD2: Setting ParamsIn, length 44

     *Mar 1 01:51:31.587: PAD2: Output X29 packet type 6 (Set and Read) len 9
     2:0, 4:1, 15:0, 7:21,
     *Mar 1 01:51:31.599: PADTCP2: Telnet received WILL ECHO (1)
     *Mar 1 01:51:31.599: PAD2: Control packet received.
     *Mar 1 01:51:31.607: PADTCP2: Telnet received DO TTY-TYPE (24)
     *Mar 1 01:51:31.611: PAD2: Output X29 packet type 6 (Set and Read) len 3 2:0,
     *Mar 1 01:51:31.619: PAD2: Input
     *Mar 1 01:51:31.619: PAD2: Control packet received.X29 packet type 0
     (Parameter indication) len 9 2:0, 4:1, 15:0, 7:21,
     *Mar 1 01:51:31.627: PAD2: Setting ParamsIn, length 8
     *Mar 1 01:51:31.631: PAD2: Input X29 packet type 0 (Parameter indication) len 3 2:0,
     *Mar 1 01:51:31.635: PAD2: Setting ParamsIn, length 2
     *Mar 1 01:51:31.643: PADTCP2: Telnet received DONT TTY-LOCATION (23)
     *Mar 1 01:51:31.647: PADTCP2: Telnet received DONT TTY-SPEED (32)

     Router2#
     Router2#show x25 vc
     SVC 1024, State: D1, Interface: Serial0
     Started 00:00:10, last input 00:00:07, output 00:00:05
     Line: 2 vty 0 Location: Host: 123
     123 connected to 345 PAD <--> X25
     Window size input: 2, output: 2
     Packet size input: 128, output: 128
     PS: 1 PR: 6 ACK: 6 Remote PR: 1 RCNT: 0 RNR: no
     P/D state timeouts: 0 timer (secs): 0
     data bytes 3057/60 packets 33/6 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0

     Router2#
     Router2#

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

I hope you found this article to be of use and it helps you prepare for your Cisco CCNP certification. I am sure you will quickly find out that hands-on real world experience is the best way to cement the CCNP concepts in your head to help you pass your CCNP exam!