Configure X.25 directory

configure LAPB

Tasks list of X.25 configuration

configure X.25 interface

configure other X.25 interface parameter

configure X.25 data transportation

Configure annex X.25 characters of transporting data message

configure X.25-TCP switching parameter

configure PVC switching among X.25 interfaces

configure SVC switching among X.25 interfaces

configure XOT switching among X.25 interfaces

configure X.25-TCP switching gateway

monitor and maintain LAPB and X.25

Examples of configurations of X.25 and LAPB

Example of typical configurations of LAPB

Example of typical configurations of X.25

This chapter will introduce how to setup network link through LAPB and X.25.

X.25 is a credible data transportation protocol face to linking, it mainly includes LAPB of OSI data link layer and X.25 of network layer.

X.25 defines two types of hosts: DTE and DCE. The router which use X.25 encapsulation can be used as DTE or DCE equipments, this is different from hardware DTE and DCE.  

More details ,please refer to the chapter of X.25 and LAPB commands in WAN commands references. Other commands, please  use command index.

configure LAPB

LAPB of X.25 work in data link layer of OSI reference model.

LAPB defines ways to switch data(its unit is frame),detect no-order frame, losing frame, re-transmitted frame, response frame on special link . These parameters are fit for X.25 link because X.25 work on group layer of LAPB.

Table-5 Some parameters and their defaults

table 1LAPB parameter

command

purpose (LAPB parameter)

Parameter values

default

x25 mod modulus

Set module value

8 or128

8

x25 k window-size

Set windows sizes(K)

2(module-1)frame

7

x25 n1 bytes

Set max bytes of each frame(N1)

137-1512

1500

x25 n2 tries

Set the counter of transmitting frame(N2)

1-255 times

16

x25 t1 seconds

Set re-transmitting timer (T1)

1-64 seconds

3

x25 t2 seconds

Set the timer of overtime receiving T2

1-32 seconds

0

l     Module value of LAPB and LAPB KLAPB decide operation mode. Module 8 is used widly because it accords all standard LAPB and is enough for most links.

Module 128 can get bigger throughput on high speed link with low error ratio through adding the numbers of transmittable frames before transportation validate (configure by parameter K in LAPB window).  

According to such a define, parameter K of LAPB can set 1 less than the value of operation value. Module 8 often transmit 7 frames before validate receiving frames. Module can set the value of K 127. If default, LAPB use the basic mode when the size of window is 7.

l     LAPB N1-when connectting X.25 network, user use N1 parameter set by network manager. This parameter is the most bytes in LAPB frame, it decides the size of X.25 group.  

Parameter N1 should be equal to the value of  MTU through hired line. The value of N1 has limited effects on interface MTU. If it does not configure properly , it will leads link failure easy. The suggestion is to keep the default value.

l      LAPB N2the counter of transportation (N2) shows the retransmitted times before  cutting link.

l      LAPB T1- The counter of retransmitted (T1), it decides how long the transmitted frame can keep not to be validated before the router receive the validated frame. For X.25 network, the setting of retransmitted timer must match the configurations of network.

l      LAPB T2— T2 value of DTE equipment can be different from the value of T2,but should note  the opposite party. When T2 is up, DTE(DCE) must transmit validated frame, so that the opposite party can receive the validated frame before his T1 is up(T2<T1).

The configuration of T1 timer is very important for hired line, because the design of LAPB assume that if the frame has not received before T1,it had losed.

The configuration of the timer must be enough big to permit the biggest frame to come and back one time. If the timer is too small, the software will poll before validate to back, this will lead frame retransmitted and serious protocol problems. If the timer is too big, the software will wait longer than necessary time, this will reduce band- width.

An example to configure LAPB T1 timer, please refer to “examples of typical LAPB configurations”.

 

Tasks list of X.25 configurations

User should do as follows to configure X.25.

Interface, data message transportation and route tasks is usually divided to parts by common characters and using frequency. We have discussed before that user can modify LAPB frame parameter to optimize X.25 operations.

configure X.25 interface

configure other X.25 interface parameter

configure X.25 data transportation

Configure annex X.25 characters of transporting data message

configure X.25-TCP switching parameter

configure PVC switching among X.25 interfaces

configure SVC switching among X.25 interfaces

configure XOT switching among X.25 interfaces

configure X.25-TCP switching gateway

monitor and maintain LAPB and X.25

All these characters can exist in X.25 interface together.

Though X.25 has default parameters, user can change these settings to meet X.25 network, or supplier can change these parameters. D-Link also provides annex configurations to optimize X.25.  

Note : If user connect the router to network by X.25 ,user must use the parameters that set by the network manager. These parameters are described in “configure X.25 interface” and “configure LAPB”. And user also should note that parameter of L2 of X.25 in ”configure LAPB”  will affect operations on L3 of X.25.  There is an example of configuring X.25 at the bottom of this chapter.

configure X.25 interface

User should do as follows to configure X.25 interface:

l      encapsulate X.25 protocol

l      set X.25 mode

l      set the range of virtual circuit

l      set X.121 address

l      set default controlling values of flux

These tasks describe important parameters to X.25, the first task is necessary, others are demanded or optional, this is depended on the type of router link X.25. 

encapsulate X.25 protocol

User must encapsulate X.25 protocol in interface configuration mode before configure X.25

command

purpose

encapsulation x25

Encapsulate X.25

set X.25 mode

The router using X.25 encapsulation can be use as DTE or DCE (up to supplier).

User need to use following commands to configure operation mode of appointed interface:

command

purpose

x25 interface [dte|dce]

Set X.25 operation mode

The default operation mode is DTE.

There is an example of configuring X.25 DTE operation in the paragraph of “an example of typical X.25 configurations”.

set the range of virtual curcuit

X.25 maintain several connections on a physical link line between DTE nd DCE. These connections are called virtual circuit(VC) or logic circuit(LC).X.25 can maintain 4095 virtual circuits numbered from 1 to 4095. A annex virtual circuit can be signed by logic circuit nuber (LCN) or virtual circuit number(VCN) . 

Many documents use VC, LC, VCN and LCN to express virtual circuit , each of them express the number of virtual circuit.  

A important part of X.25 is the range of virtual circuit numbers. Virtual circuit numbers can be divides to two ranges:(list by value adding)

1.    permanent virtual circuit

2.      switching virtual circuit

SVC can be created by X.25 call, this is very like to telephone network to create switching voice circuit when creating call.  

Note: in this manual, except to use ITU-T, or call received on interface is call-in, and call transmitted on interface is call-out. 

Because X.25 need DTE and DCE have the same range of virtual circuit, when the interface is connecting, the change of the range limit will keep until X.25 restart group service. 

User can use following commands to configure the range of X.25 virtual circuit:

command

purpose

range

default

x25 htc circuit-number

Set the highest virtual circuit number

1-4095

1024

x25 pvc circuit-number

Set the highest permanent virtual circuit number

0-1024

0

User must keep the values of two terminals of X.25 link line same. These values must be set to the values assigned by network.  

If the range of PVC is equal to the top limit of VC, it is not necessary to use SVC. Besides the signed range, virtual circuit 0 can not be sed. 

There is an example of configure the range of virtual circuit in “an example of the range of virtual circuit”.

Set X.121 address

If using the router as a X.25 switch, user does not need to configure X.121 address. If the router connect PDN, user must configure X.121 address of interface.  

User can use following commands to configure X.121 address:

command

purpose

x25 address x121-address

configure X.121 address

More details about configurations mode of X.25 interface’s address, please refer to ” an example of typical X.25 configuration”.   

 

set default controlling values of flux

It is necessary to set the size of windows to control flux and data packet because X.25 suggest to use flux controlling protocol mightily. Because many networks use the default ,user can overlook this value easy. The mistook value of flux controlling may leads to X.25 local error.

User can do as follows to configure the parameters of flux controlling  

l      set the size of default window

l      set the size of default frouping

User can use following commands to configure the values of X.25 flux controlling:

command

purpose

range

default

x25 psize size

Set the size of grouping(bytes)

128,256,512,1024

128

x25 wsize packets

Set the size of window

2-(module-1)

2

Note: X.25 needs DTE and DCE have default max sizes of windows and data grouping. When interface is connecting, it will restart the protocol if user change the mode.

configure other X.25 interface parameters 

Some applications of X.25 do not work often, some parameters can use to modify X.25 protocol:

User need do as follows to configure other interface parameters of X.25:

l      configure X.25 timer

l      configure X.25 address

configure X.25 timer

User need to use following commands to configure timer:

command

purpose

x25 t20 seconds

Set DTE T20 restart request is over time, default is  180seconds.

x25 t23 seconds

Set DTE T23 to clear over time request, default is 180 seconds.

There is an example an example of typical configurations of X.25.

configure X.25 address

X.25 use X.121 defined by ITU-T to create SVC. The address of X.121 changes from 0-15 digit, because the importance of addresses created by call, there are some interface address characters to X.25.  

User need to do as follows to configure X.25 address:

l      understand normal X.25 address

l      configure the byname address of interface

understand normal X.25 address

If it is X.25 call source or destination, use X.121 address on X.25 interface. The course of create call of X.25 appoint the addresses of source and X.121. When the interface is call source, the X.121 address of the interface is source address. If destination address matches the interface address, the interface is the destnation of the received call.

The X.25 module of the router can route X.25 call including receiving and process call, but the router is not the source or destination of call. Route X.25 will not change the addresses of source or destination, but keep appointed address by source host. Route X.25 is just simply to connect logic X.25 channels to finish switching among several X.25 connecting. 

 

configure the byname address of interface

X.121 address byname is supported on a interface, this permit to treat the interface as destination host when the destination address of a call is not the interface address or null.  

Local processing (like IP encapsulation) can only execute call-in. Its destination X.121 is match to the serial or the byname of the interface. 

Use following commands to configure the bynames: 

command

purpose

[no] x25 alias [string]

Use X.121 address byname on the interface

configure X.25 data transportation

Supporting X.25 is the most common configurations on X.25 network to transport data. Data transportation work by co-operations among X.25 hosts. It can transport data packet through creating map between the addresses of remote hosts’ protocols and the address of local X.121.    

User need to do as follows to finish X.25 configurations:

l      map the address of the protocol to X.121 address

map the address of the protocol to X.121 address

This paragraph introduces map operations of X.25 protocol addresses, and introduces how to  map X.121 address for a remote host.

Encapsulation is a co-operation course between X.25 host and the router. Because X.25 host arrives by the address of X.121, the router must map the host protocols and addresses to X.121 address.

Each encapsulation X.25 interface must configure corresponding data grouping parameters. For example, there is a IP address on the interface with X.25. 

User need to use command”X.25 address “to configure X.121 address for the interface encapsulated X.25 protocol.  This is source address of  X.25 call; is also used as destination protocol address by destination hosts . Encapsulation virtual circuit need to create map on the interfaces between source and destination hosts.    

For each X.25 interface, it need to map each destination host protocol to X.121 address.  

If needed and the destination host has the ability, one host map must configure to support several protocols, and define a interface for each supported protocol. 

Use following commands to create map:

command

purpose

[no] x25 map ipaddress pvc pvc_no [broadcast]

Add/delete one permanent virtual circuit comparison

[no] x25 map ipaddress svc x121-address [broadcast][ebackup]

Add/delete one switching virtual circuit comparison

Ebackup expresses the address map is an enforced backup kind.

Note: multi-protocol map, especially with broadcast communication, can lead to big communication load, it needs bigger queque, windows or more virtual circuits. User can add “broadcast” to appoint the configurations of OSPF protocol. Refer to command map in “commands of X.25 and LAPB”.   

map destination X.121 address to a logic virtual interface

This chapter will introduce how to configure a router to help remote computers connect to LAN through X.25 network.

First, remote computers connect PSDN network( or connect X.25 directly ) by a normal dialing way, the network providers transfer call to X.25 network through PAD. PAD help to finish creating call.

At that time, the course of throwin experience the transferring from asychronism to synchronization and leads to PPP over X.25 dialing way.

If the local router has configured the map from destination X.121 address to a logic virtual interface, it will accept call, and  turn call to PPP dial-in service to finish authentication, accounting, authorization and so on. After passing authentication, the remote computer can access LAN.

Use following commands:

command

function

[no] translate x25 x121-address virtual-template virtual-template-interface-number

add/delete one map from X.121 to virtual circuit.

the following is basic configuration chart:

          chart 1 an typical configuration chart mapping X.121 address to virtual interface

 

Configure annex X.25 characters of transporting data message

The software of the router permit to configure annex X.25 characters of transporting data message, the grouping include many user characters for x.25 call.

Use following parameters to configure:

Do as follows to configure optional parameters, user and other characters:   

l      configure virtual circuit leisure time encapsulation

l      configure X.25 negotiation parameters

configure virtual circuit leisure time encapsulation

The router can clear switching virtual circuits after a leisure time.

Use following commands to set this time:

command

purpose

x25 idle seconds

set leisure time to clear virtual circuits. Range(0-214783647), default is 100 seconds.

More details ,refer to an example of typical X.25 configurations.

configure X.25 negotiation parameters

The software of X.25 supports to configure x.25 negotiation parameters. It permits to use the functon of D byte location, the function to negotiate the length of grouping, the function to negotiate the size of grouping windows, the function to take main call address in X.25 call request grouping.  

Use following commands to set supported X.25 negotiation parameters:

command

purpose

[no] x25 dbit

set to whether permit D byte location or not

[no] x25 nps

open /close the function of negotiation  the length of grouping

[no] x25 nws

Open/close the function to negotiate the size of grouping windows

[no] x25 cwla

the function to take main call address in X.25 call request grouping.

configure X.25-tcp switching paramters

Use following commands:(only limited to part tested versions)

command

purpose

[no] x25 tcp user-data line

set user data used by X.25-tcp on the interface

[no] x25 tcp pkt-format [rfc1006|transparent|user]

set the message format of switching

[no] x25 tcp iso-address line

set iso extensible address used by X.25-tcp on this interface

 

configure PVC switching among X.25 interfaces

This router can be used as X.25 switch. This include PVC switching and SVC switching. The two interfaces used as PVC switching must have PVC which is not used yet.

Use following commands in configuration mode:

command

Purpose

[no] x25switch connect port1 port1_pvc_no port2 port2_pvc_no

configure PVC switching

When to configure switch table,  the two connecting interfaces must save to effective permanent virtual circuit. 

configure SVC switching among X.25 interfaces

The sizes of windows and groupings of two sides hosts can be different through switch, it will be set to the smaller one through switch module.

Use following commands in configuration mode:

command

Purpose

[no] x25switch destination [x121addr/default] port

Configure a SVC interface addressing

configure XOT switching among X.25 interfaces

It can switch X.25 message on TCP/IP through the router.

Use following commands in configuration mode:

command

Purpose

[no] x25switch xot pvc local-interface local-pvc remote-interface remote-pvc remote-ip-address [source interface]

configure one PVC XOT interface addressing

[no] x25switch xot svc x.121-address remote-ip-address [source interface]

configure one SVC XOT interface addressing

 

configure X.25-TCP switching gateway

It can switch messages between X.25 and TCP through the router.

Use following commands in configuration mode:

command

Purpose

[no] translate tcp ip ip-address svc intr1 x121address1 lport locport rport remport [backup intr2 x121address2]

configure a map from source IP address to destination X.121 address, and TCP interception interface of local and remote

 

 

[no] translate tcp ip ip-address pvc intr1 pvc#1 lport locport rport remport [backup intr2 pvc#2]

configure a map from source IP address to destination PVC address, and TCP interception interface of local and remote

 

monitor and maintain LAPB and X.25

To monitor and maintain X.25 and LAPB, use following commands in management mode:

command

Purpose

clear x25 port vc-number

Clear SVC

show interface serial number

show running statistics information on the interface

show x25

show X.25 interface address map table

show x25switch

show X.25 switching table inforamtion

[no] debug lapb [iframes|sframes|uframes|raw]serial

debug all kinds of frame by LAPB

[no] debug x25 [events|normal|raw|xot]serial

debug X.25 internal events and messages

[no] debug x25 xot

debug XOT setup cources

[no] debug x25 tcp [data|event|list]

debug events, data receiving and transmitting , status of link line of X.25-TCP

Examples of configurations of X.25 and LAPB

Some examples to help to understand how to configure LAPB and X.25.

Example of typical configurations of LAPB

In the following example, the size of frame N1, the size of windows K and the max retransmit parameter N2 keep their defaults.Command Encapsulation make DCE to load a independent protocol (default is IP protocol). Command X.25 set the retransmit timer to 4 seconds, use to long delay of DTE or slow connecting.

Router_config# interface s1/0

Router_config_s1/0#encapsulation x25

Router_config_s1/0#x25 interface dce

Router_config_s1/0#x25 t1 4

Example of typical configurations of X.25

This chapter will introduce you an example of typical configurations of x.25 to help you to understand related tasks and contents of X.25 of D-Link series routers. In this chapter, the content behind “!” is note, it can not be input in commands.

To connect two routers through back-to-back serials simply

1network requirements

If you only want to connect two routers back-to-back simply, encapsulate X.25 between serials and load IP data message to transport, you just need to configure two routers as follows.

2network chart

   

chart 2  two routers connect directly through serials

3configuration steps

! configure Router A:

! choose interface

Router#config

Router_config#interface s1/0

! appoint IP address for the interface

Router_config_s1/0#ip address 202.38.160.1 255.255.255.0

!  encapsulate this interface to X.25 interface and make it work in DTE mode

Router_config_s1/0#encapsulation x25

! appoint X.121 address of this interface

Router_config_s1/0#x25 address 20112451

! appoint the address map to the opposite terminal

Router_config_s1/0#x25 map 202.38.160.2 svc 20112452

!configure Router B:

! choose interface

Router#config

Router_config#interface s1/0

! appoint IP address for the interface

Router_config_s1/0#ip address 202.38.160.2 255.255.255.0 

!set interface speed

Router_config_s1/0#physical-layer speed 64000

! encapsulate this interface to X.25 interface and make it work in DCE mode

Router_config_s1/0#encapsulation x25

Router_config_s1/0#x25 interface dce

! appoint X.121 address of this interface

Router_config_s1/0#x25 address 20112452

! appoint the address map to the opposite terminal

Router_config_s1/0#x25 map 202.38.160.1 svc 20112451

connect the router to X.25 public grouping network

1network requirements

Router A, router B and router C are connected to the same X.25 network :

requirements :IP addresses of serial 1/0 of three routers are 168.173

.24.1, 168.173.24.2,168.173.24.3 by turns; 

The X.121 addresses of three routers assigned by network are 30561001,30561002,30561003;

The size of standard window supported by sub-network: receiving window is 5 and transmitting window is 5; 

standard max grouping length: max receiving grouping length is 512 and max transmitting grouping length is 512;  

Channel range: 1—32.

2network char

      

chart 3 to connect the router to X.25 public grouping netwrok

3configure steps

configure router A:

!  configure interface IP address

Router#config

Router_config#interface s1/0

Router_config_s1/0#ip address 168.173.24.1 255.255.255.0

! connect to public grouping network, let the router be DTE:

Router_config_s1/0#encapsulation x25

Router_config_s1/0#x25 address 30561001

Router_config_s1/0#x25 htc 32

Router_config_s1/0#x25 map 168.173.24.2 svc 30561002

Router_config_s1/0#x25 map 168.173.24.3 svc 30561003

configure router B:

! configure interface IP address

Router#config

Router_config#interface s1/0

Router_config_s1/0#ip address 168.173.24.2 255.255.255.0

! connect to public grouping network, let the router be DTE:

Router_config_s1/0#encapsulation x25

Router_config_s1/0#x25 address 30561002

Router_config_s1/0#x25 htc 32

Router_config_s1/0#x25 map 168.173.24.1 svc 30561001

Router_config_s1/0#x25 map 168.173.24.3 svc 30561003

configure router C:

! configure interface IP address

Router#config

Router_config#interface s1/0

Router_config_s1/0#ip address 168.173.24.3 255.255.255.0

! connect to public grouping network, let the router be DTE:

Router_config_s1/0#encapsulation x25

Router_config_s1/0#x25 address 30561003

Router_config_s1/0#x25 htc 32

Router_config_s1/0#x25 map 168.173.24.1 svc 30561001

Router_config_s1/0#x25 map 168.173.24.2 svc 30561002

configure the range of virtual circuit

After executing following commands, serial 1/0 of the router will be encapsulated X.25, and the range of virtual circuit is : permanent virtual circuit is [1,8],switching virtual circuit is [9,64].

Router#config

Router_config#interface s1/0

Router_config_s1/0#encapsulation x25

Router_config_s1/0#x25 htc 64

Router_config_s1/0#x25 pvc 8

Example of XOT configuration based on PVC

  The following is configuration chart and commands:

chart 4  XOT configurations chart based on PVC

configure router B1:

Router_config_s1/1#ip address 8.0.0.1 255.0.0.0

Router_config_s1/1#enc x25

Router_config_s1/1#x25 interface dce

Router_config_s1/1#x25 pvc 2

Router_config_s1/1#x25 map 8.0.0.10 pvc 1

configure router C1:

Router_config_f0/0#ip address 192.168.20.92 255.0.0.0

Router_config_s1/0#ip address 8.0.0.2 255.0.0.0

Router_config_s1/0#enc x25

Router_config_s1/0#x25 pvc 2

Router_config#x25switch xot pvc serial 1/0 1 serial 1/1 1 192.168.20.22

configure router C2:

Router_config_f0/0#ip address 192.168.20.22 255.0.0.0

Router_config_s1/1#ip address 8.0.0.11 255.0.0.0

Router_config_s1/1#enc x25

Router_config_s1/1#x25 pvc 2

Router_config#x25switch xot pvc serial 1/1 1 serial 1/0 1 192.168.20.92

configure router B2:

Router_config_s1/0#ip address 8.0.0.10 255.0.0.0

Router_config_s1/0#enc x25

Router_config_s1/0#x25 interface dce

Router_config_s1/0#x25 pvc 2

Router_config_s1/0#x25 map 8.0.0.1 pvc 1

Example of configure X.25-TCP switching

The following is configuration chart and commands:

chart 5  X.25-TCP configurations chart

configure router B1:

ROUTER-CONFIG#translate tcp ip 192.168.20.130 svc s1/0 111 lport 2000 rport 2000

ROUTER-CONFIG-S1/0# encapsulation x25

ROUTER-CONFIG-S1/0# x25 address 222

ROUTER-CONFIG-S1/0# x25 tcp user-data 03010100

ROUTER-CONFIG-S1/0# x25 tcp pkt-format RFC1006

ROUTER-CONFIG-S1/0# x25 tcp iso-address 000fc909103600001111cb09103600002222

ROUTER-CONFIG-F1/0# ip address 192.168.20.131 255.255.255.