- Cisco IOS Wide-Area Networking Command Reference, Release 12.2
Table Of Contents
X.25 and LAPB Commands
Use the commands in this chapter to configure the following:
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Link Access Procedure, Balanced (LAPB)
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X.25 provides remote terminal access and bridging. X.25 also provides encapsulation for the following protocols:
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X.25 virtual circuits can be switched as follows:
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To translate between X.25 and another protocol, refer to the chapter "Configuring Protocol Translation and Virtual Asynchronous Devices" in the Cisco IOS Terminal Services Configuration Guide.
For X.25 and LAPB configuration information and examples, refer to the "Configuring X.25 and LAPB" chapter in the Cisco IOS Wide-Area Networking Configuration Guide.
access-class (X.25)
To configure an incoming access class on virtual terminals, use the access-class (X.25) line configuration command.
access-class access-list-number in
Syntax Description
access-list-number
An integer from 1 to 199 that you select for the access list.
in
Restricts incoming connections between a particular access server and the addresses in the access list.
Defaults
No incoming access class is defined.
Command Modes
Line configuration
Command History
Usage Guidelines
The access list number is used for both incoming Transmission Control Protocol (TCP) access and incoming packet assembler/disassembler (PAD) access.
In the case of TCP access, the access server uses the IP access list defined with the access-list command.
For incoming PAD connections, the same numbered X.29 access list is referenced. If you only want to have access restrictions on one of the protocols, you can create an access list that permits all addresses for the other protocol.
Examples
The following example configures an incoming access class on virtual terminal line 4. For information on the line vty command see the publication Configuring the Route Processor for the Catalyst 8540 and Using Flash Memory Cards.
line vty 4access-class 4 inRelated Commands
access-list
Configures the access list mechanism for filtering frames by protocol type or vendor code.
Limits access to the access server from certain X.25 hosts.
bfe
This command is no longer supported.
clear x25
To restart an X.25 service or Connection-Mode Network Service (CMNS), to clear a switched virtual circuit (SVC), or to reset a permanent virtual circuit (PVC), use the clear x25 privileged EXEC command.
clear x25 {serial number | {ethernet | fastethernet | tokenring | fddi} number mac-address} [vc-number] | [dlci number]
Syntax Description
Command Modes
Privileged EXEC
Command History
Usage Guidelines
This command form is used to disrupt service forcibly on an individual circuit or on all circuits using a specific X.25 service or CMNS service.
If this command is used without the vc-number value, a restart event is initiated, which implicitly clears all SVCs and resets all PVCs.
This command allows the option of restarting an Annex G connection per data-link connection identifier (DLCI) number, clearing all X.25 connections, or clearing a specific X.25 logical circuit number on that Annex G link.
Examples
The following example clears the SVC or resets the PVC specified:
clear x25 serial 0 1The following example forces an X.25 restart, which implicitly clears all SVCs and resets all PVCs using the interface:
clear x25 serial 0The following example restarts the specified CMNS service (if active), which implicitly clears all SVCs using the service:
clear x25 ethernet 0 0001.0002.0003The following example clears the specified DLCI Annex G connection (40) from the specified interface:
clear x25 serial 1 40Related Commands
clear x25-vc
This command is replaced by the clear x25 command. See the description of the clear x25 command earlier in this chapter for more information.
clear xot
To clear an X.25 over TCP (XOT) switched virtual circuit (SVC) or reset an XOT permanent virtual circuit (PVC), use the clear xot EXEC command.
clear xot remote ip-address port local ip-address port
Syntax Description
remote ip-address port
Remote IP address and port number of an XOT connection ID.
local ip-address port
Local IP address and port number of an XOT connection ID.
Command Modes
EXEC
Command History
Usage Guidelines
Each SVC or PVC supported by the XOT service uses a TCP connection to communicate X.25 packets. A TCP connection is uniquely identified by the data quartet: remote IP address, remote TCP port, local IP address, and local TCP port. This command form is used to forcibly disrupt service on an individual XOT circuit.
XOT connections are sent to TCP port 1998, so XOT connections originated by the router will have that remote port number, and connections received by the router will have that local port number.
Examples
The following command will clear or reset, respectively, the SVC or PVC using the TCP connection identified:
clear xot remote 10.1.1.1 1998 local 172.2.2.2 2000Related Commands
cmns enable
To enable the Connection-Mode Network Service (CMNS) on a nonserial interface, use the cmns enable interface configuration command. To disable this capability, use the no form of this command.
cmns enable
no cmns enable
Syntax Description
This command has no arguments or keywords.
Defaults
Each nonserial interface must be explicitly configured to use CMNS.
Command Modes
Interface configuration
Command History
Usage Guidelines
After this command is processed on the LAN interfaces—Ethernet, Fiber Distributed Data Interface (FDDI), and Token Ring—all the X.25-related interface configuration commands are made available.
Examples
The following example enables CMNS on Ethernet interface 0:
interface ethernet 0cmns enableRelated Commands
Creates an entry in the X.25 routing table (to be consulted for forwarding incoming calls and for placing outgoing PAD or protocol translation calls).
encapsulation lapb
To exchange datagrams over a serial interface using Link Access Procedure, Balanced (LAPB) encapsulation, use the encapsulation lapb interface configuration command.
encapsulation lapb [dte | dce] [multi | protocol]
Syntax Description
Defaults
The default serial encapsulation is High-Level Data Link Control (HDLC). You must explicitly configure a LAPB encapsulation method.
DTE operation is the default LAPB mode. IP is the default protocol.
Command Modes
Interface configuration
Command History
10.0
This command was introduced.
10.3
The following keywords and argument were introduced:
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Usage Guidelines
LAPB encapsulations are appropriate only for private connections, where you have complete control over both ends of the link. Connections to X.25 networks should use an X.25 encapsulation configuration, which operates the X.25 Layer 3 protocol above a LAPB Layer 2.
One end of the link must be a logical DCE device, and the other end a logical DTE device. (This assignment is independent of the interface's hardware DTE or DCE identity.)
Both ends of the LAPB link must specify the same protocol encapsulation.
LAPB encapsulation is supported on serial lines configured for dial-on-demand routing (DDR). It can be configured on DDR synchronous serial and ISDN interfaces and on DDR dialer rotary groups. It is not supported on asynchronous dialer interfaces.
A single-protocol LAPB encapsulation exchanges datagrams of the given protocol, each in a separate LAPB information frame. You must configure the interface with the protocol-specific parameters needed—for example, a link that carries IP traffic will have an IP address defined for the interface.
A multiprotocol LAPB encapsulation can exchange any or all of the protocols allowed for a LAPB interface. It exchanges datagrams, each in a separate LAPB information frame. Two bytes of protocol identification data precede the protocol data. You need to configure the interface with all the protocol-specific parameters needed for each protocol carried.
Beginning with Cisco IOS Release 11.0, multiprotocol LAPB encapsulation supports transparent bridging. This feature requires use of the encapsulation lapb multi command followed by the bridge-group command, which identifies the bridge group associated with multiprotocol LAPB encapsulation. This feature does not support use of the encapsulation lapb protocol command with a bridge keyword.
Beginning with Release 10.3, LAPB encapsulation supports the priority and custom queueing features.
Examples
The following example sets the operating mode as DTE and specifies that AppleTalk protocol traffic will be carried on the LAPB line:
interface serial 1encapsulation lapb dte appletalkRelated Commands
encapsulation x25
To specify a serial interface's operation as an X.25 device, use the encapsulation x25 interface configuration command.
encapsulation x25 [dte | dce] [ddn | bfe] | [ietf]
no encapsulation x25 [dte | dce] [ddn | bfe] | [ietf]
Syntax Description
Defaults
The default serial encapsulation is High-Level Data Link Control (HDLC). You must explicitly configure an X.25 encapsulation method.
DTE operation is the default X.25 mode. Cisco's traditional X.25 encapsulation method is the default.
Command Modes
Interface configuration
Command History
10.0
This command was introduced.
10.3
The following keywords were added:
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Usage Guidelines
One end of an X.25 link must be a logical DCE device and the other end a logical DTE device. (This assignment is independent of the interface's hardware DTE or DCE identity.) Typically, when connecting to a public data network (PDN), the customer equipment acts as the DTE device and the PDN attachment acts as the DCE.
Cisco has long supported the encapsulation of a number of datagram protocols, using a standard means when available and a proprietary means when necessary. More recently the IETF adopted a standard, RFC 1356, for encapsulating most types of datagram traffic over X.25. X.25 interfaces use Cisco's traditional method unless explicitly configured for IETF operation; if the ietf keyword is specified, that standard is used unless Cisco's traditional method is explicitly configured. For details see the x25 map command.
You can configure a router attaching to the DDN or to a BFE device to use their respective algorithms to convert between IP and X.121 addresses by using the ddn or bfe option, respectively. An IP address must be assigned to the interface, from which the algorithm will generate the interface's X.121 address. For proper operation, this X.121 address must not be modified.
A router DDN attachment can operate as either a DTE or a DCE device. A BFE attachment can operate only as a DTE device. The ietf option is not available if either the ddn or bfe option is selected.
Examples
The following example configures the interface for connection to a BFE device:
interface serial 0encapsulation x25 bfeRelated Commands
lapb interface-outage
To specify the period for which a link will remain connected, even if a brief hardware outage occurs (partial Link Access Procedure, Balanced [LAPB] T3 timer functionality), use the lapb interface-outage interface configuration command.
lapb interface-outage milliseconds
Syntax Description
milliseconds
Number of milliseconds (ms) a hardware outage can last without the protocol disconnecting the service.
Defaults
0 ms, which disables this feature.
Command Modes
Interface configuration
Command History
Usage Guidelines
If a hardware outage lasts longer than the LAPB hardware outage period you select, normal protocol operations will occur. The link will be declared down, and when it is restored, a link setup will be initiated.
Examples
The following example sets the interface outage period to 100 ms. The link remains connected for outages equal to or shorter than that period.
encapsulation lapb dte iplapb interface-outage 100Related Commands
lapb k
To specify the maximum permissible number of outstanding frames, called the window size, use the lapb k interface configuration command.
lapb k window-size
Syntax Description
window-size
Frame count. It can be a value from 1 to the modulo size minus 1 (the maximum is 7 if the modulo size is 8; it is 127 if the modulo size is 128).
Defaults
7 frames
Command Modes
Interface configuration
Command History
Usage Guidelines
If the window size is changed while the protocol is up, the new value takes effect only when the protocol is reset. You will be informed that the new value will not take effect immediately.
When using the Link Access Procedure, Balanced (LAPB) modulo 128 mode (extended mode), you must increase the window parameter k to send a larger number of frames before acknowledgment is required. This increase is the basis for the router's ability to achieve greater throughput on high-speed links that have a low error rate.
This configured value must match the value configured in the peer X.25 switch. Nonmatching values will cause repeated LAPB reject (REJ) frames.
Examples
The following example sets the LAPB window size (the k parameter) to 10 frames:
interface serial 0lapb modulolapb k 10Related Commands
lapb modulo
To specify the Link Access Procedure, Balanced (LAPB) basic (modulo 8) or extended (modulo 128) protocol mode, use the lapb modulo interface configuration command.
lapb modulo modulus
Syntax Description
modulus
Either 8 or 128. The value 8 specifies LAPB's basic mode; the value 128 specifies LAPB's extended mode.
Defaults
Modulo 8
Command Modes
Interface configuration
Command History
Usage Guidelines
The modulo parameter determines which of LAPB's two modes is to be used. The modulo values derive from the fact that basic mode numbers information frames between 0 and 7, whereas extended mode numbers them between 0 and 127. Basic mode is widely available and is sufficient for most links. Extended mode is an optional LAPB feature that may achieve greater throughput on high-speed links that have a low error rate.
The LAPB operating mode may be set on X.25 links as well as LAPB links. The X.25 modulo is independent of the LAPB layer modulo. Both ends of a link must use the same LAPB mode.
When using modulo 128 mode, you must increase the window parameter k to send a larger number of frames before acknowledgment is required. This increase is the basis for the router's ability to achieve greater throughput on high-speed links that have a low error rate.
If the modulo value is changed while the protocol is up, the new value takes effect only when the protocol is reset. You will be informed that the new value will not take effect immediately.
Examples
The following example configures a high-speed X.25 link to use LAPB's extended mode:
interface serial 1encapsulation x25lapb modulo 128lapb k 40clock rate 2000000Related Commands
Specifies the maximum permissible number of outstanding frames, called the window size.
lapb n1
To specify the maximum number of bits a frame can hold (the Link Access Procedure, Balanced [LAPB] N1 parameter), use the lapb n1 interface configuration command.
lapb n1 bits
Syntax Description
bits
Maximum number of bits in multiples of eight. The minimum and maximum range is dynamically set. Use the question mark (?) to view the range.
Defaults
The largest (maximum) value available for the particular interface is the default. The Cisco IOS software dynamically calculates N1 whenever you change the maximum transmission unit (MTU), the L2/L3 modulo, or compression on a LAPB interface.
Command Modes
Interface configuration
Command History
Usage Guidelines
The Cisco IOS software uses the following formula to determine the minimum N1 value:
(128 (default packet size) + LAPB overhead + X.25 overhead + 2 bytes of CRC) * 8
The Cisco IOS software uses the following formula to determine for the maximum N1 value:
(hardware MTU + LAPB overhead + X.25 overhead + 2 bytes of CRC) * 8
LAPB overhead is 2 bytes for modulo 8 and 3 bytes for modulo 128.
X.25 overhead is 3 bytes for modulo 8 and 4 bytes for modulo 128.
You need not set N1 to an exact value to support a particular X.25 data packet size. The N1 parameter prevents the processing of any huge frames that result from a "jabbering" interface, an unlikely event.
In addition, the various standards bodies specify that N1 be given in bits rather than bytes. While some equipment can be configured in bytes or will automatically adjust for some of the overhead information present, Cisco devices are configured using the true value, in bits, of N1.
You cannot set the N1 parameter to a value less than that required to support an X.25 data packet size of 128 bytes. All X.25 implementations must be able to support 128-byte data packets. Moreover, if you configure N1 to be less than 2104 bits, you receive a warning message that X.25 might have problems because some nondata packets can use up to 259 bytes.
You cannot set the N1 parameter to a value larger than the default unless the hardware MTU size is first increased.
The X.25 software accepts default packet sizes and calls that specify maximum packet sizes greater than those the LAPB layer supports, but negotiates the calls placed on the interface to the largest value that can be supported. For switched calls, the packet size negotiation takes place end-to-end through the router so the call will not have a maximum packet size that exceeds the capability of either of the two interfaces involved.
Caution
Examples
The following example shows how to use the question mark (?) command to display the minimum and maximum N1 value. In this example, X.25 encapsulation has both the LAPB and X.25 modulo set to 8. Any violation of this N1 range results in an "Invalid input" error message.
router(config)# interface serial 1router(config-if)# lapb n1 ?<1080-12056> LAPB N1 parameter (bits; multiple of 8)The following example sets the N1 bits to 16440:
router(config)# interface serial 0router(config-if)# lapb n1 16440router(config-if)# mtu 2048Related Commands
lapb n2
To specify the maximum number of times a data frame can be sent (the Link Access Procedure, Balanced [LAPB] N2 parameter), use the lapb n2 interface configuration command.
lapb n2 tries
Syntax Description
Defaults
20 transmissions
Command Modes
Interface configuration
Command History
Examples
The following example sets the N2 tries to 50:
interface serial 0lapb n2 50Related Commands
lapb protocol
The lapb protocol command has been replaced by the [protocol | multi] option of the encapsulation lapb command. See the description of the [protocol | multi] option of the encapsulation lapb command earlier in this chapter for more information.
lapb t1
To set the retransmission timer period (the Link Access Procedure, Balanced [LAPB] T1 parameter), use the lapb t1 interface configuration command.
lapb t1 milliseconds
Syntax Description
Defaults
3000 ms
Command Modes
Interface configuration
Command History
Usage Guidelines
The retransmission timer determines how long a transmitted frame can remain unacknowledged before the LAPB software polls for an acknowledgment. The design of the LAPB protocol specifies that a frame is presumed to be lost if it is not acknowledged within T1; a T1 value that is too small may result in duplicated control information, which can severely disrupt service.
To determine an optimal value for the retransmission timer, use the ping privileged EXEC command to measure the round-trip time of a maximum-sized frame on the link. Multiply this time by a safety factor that takes into account the speed of the link, the link quality, and the distance. A typical safety factor is 1.5. Choosing a larger safety factor can result in slower data transfer if the line is noisy. However, this disadvantage is minor compared to the excessive retransmissions and effective bandwidth reduction caused by a timer setting that is too small.
Examples
The following example sets the T1 retransmission timer to 2000 ms:
interface serial 0lapb t1 2000Related Commands
lapb t2
To set the explicit acknowledge deferral timer (the Link Access Procedure, Balanced [LAPB] T2 parameter), use the lapb t2 interface configuration command.
lapb t2 milliseconds
Syntax Description
milliseconds
Time in milliseconds. It can be a value from 1 to 32000. Default is 0 ms (disabled) and the recommended setting.
Defaults
0 ms (disabled), which means that the software will send an acknowledgement as quickly as possible.
Command Modes
Interface configuration
Command History
Usage Guidelines
The explicit acknowledge deferral timer determines the time that the software waits before sending an explicit acknowledgement. The acknowledgement is piggybacked with the data, unless there is no data and then an explicit acknowledgement is sent when the timer expires.
Caution
Related Commands
lapb t4
To set the T4 idle timer, after which the Cisco IOS software sends out a Poll packet to determine whether the link has suffered an unsignaled failure, use the lapb t4 interface configuration command.
lapb t4 seconds
Syntax Description
Defaults
0 seconds
Command Modes
Interface configuration
Command History
Usage Guidelines
Any non-zero T4 duration must be greater than T1, the Link Access Procedure, Balanced (LAPB) retransmission timer period.
Examples
The following example will poll the other end of an active link if it has been 10 seconds since the last frame was received. If the far host has failed, the service will be declared down after n2 tries are timed out.
interface serial0encapsulation x25lapb t4 10Related Commands
service pad
To enable all packet assembler/disassembler (PAD) commands and connections between PAD devices and access servers, use the service pad global configuration command. To disable this service, use the no form of this command.
service pad [cmns][from-xot][to-xot]
no service pad [cmns][from-xot][to-xot]
Syntax Description
cmns
(Optional) Specifies sending and receiving PAD calls over CMNS.
from-xot
(Optional) Accepts XOT to PAD connections.
to-xot
(Optional) Allows outgoing PAD calls over XOT.
Defaults
All PAD commands and associated connections are enabled. PAD services over XOT or CMNS are not enabled.
Command Modes
Global configuration
Command History
Usage Guidelines
The options from-xot and to-xot enable PAD calls to destinations that are not reachable over physical X.25 interfaces, but instead over TCP tunnels. This feature is known as PAD over XOT (X.25 over TCP).
Examples
If service pad is disabled, the EXEC pad command and all PAD related configurations, such as X.29, are unrecognized, as shown in the following example:
Router(config)# no service padRouter(config)# x29 ?% Unrecognized commandRouter(config)# exitRouter# pad ?% Unrecognized commandIf service pad is enabled, the EXEC pad command and access to an X.29 configuration are granted as shown in the following example:
Router# config terminalEnter configuration commands, one per line. End with CNTL/Z.Router(config)# service padRouter(config)# x29 ?access-list Define an X.29 access listinviteclear-time Wait for response to X.29 Invite Clear messageprofile Create an X.3 profileRouter# pad ?WORD X121 address or name of a remote systemIn the following example, PAD services over CMNS are enabled:
! Enable CMNS on a nonserial interfaceinterface ethernet0cmns enable!!Enable inbound and outbound PAD over CMNS serviceservice pad cmns!! Specify an X.25 route entry pointing to an interface's CMNS destination MAC addressx25 route ^2193330 interface Ethernet0 mac 00e0.b0e3.0d62Router# show x25 vcSVC 1, State: D1, Interface: Ethernet0Started 00:00:08, last input 00:00:08, output 00:00:08Line: 0 con 0 Location: console Host: 2193330connected to 2193330 PAD <--> CMNS Ethernet0 00e0.b0e3.0d62Window size input: 2, output: 2Packet size input: 128, output: 128PS: 2 PR: 3 ACK: 3 Remote PR: 2 RCNT: 0 RNR: noP/D state timeouts: 0 timer (secs): 0data bytes 54/19 packets 2/3 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0Related Commands
service pad from-xot
To permit incoming X.25 over TCP (XOT) calls to be accepted as a packet assembler/disassembler (PAD) session, use the service pad from-xot global configuration command. To disable this service, use the no form of this command.
service pad from-xot
no service pad from-xot
Syntax Description
This command has no arguments or keywords.
Defaults
Incoming XOT connections are ignored.
Command Modes
Global configuration
Command History
Usage Guidelines
If service pad from-xot is enabled, the calls received using the XOT service may be accepted for processing a PAD session.
Examples
The following example prevents incoming XOT calls from being accepted as a PAD session:
no service pad from-xotRelated Commands
service pad to-xot
To permit outgoing PAD sessions to use routes to an XOT destination, use the service pad to-xot global configuration command. To disable this service, use the no form of this command.
service pad to-xot
no service pad to-xot
Syntax Description
This command has no arguments or keywords.
Defaults
XOT routes pointing to XOT are not considered.
Command Modes
Global configuration
Command History
Examples
If service pad to-xot is enabled, the configured routes to XOT destinations may be used when the router determines where to send a PAD Call, as shown in the following example:
service pad to-xotRelated Commands
show cmns
Effective with Cisco IOS Release 11.3, this command is no longer available.
show x25 context
To view operating configuration status details of an X.25 link, use the show x25 context EXEC command.
show x25 context [interface number dlci number]
Syntax Description
interface number
(Optional) Specific logical X.25 virtual circuit interface.
dlci number
(Optional) Specific DLCI link.
Command Modes
EXEC
Command History
12.0(3)T
This command was introduced.
12.1(5)T
This command was modified to display information about X.25 Failover.
Examples
The following is sample output from the show x25 context command:
Router# show x25 contextSerial1 DLCI 20PROFILE DCE, address <none>, state R1, modulo 8, timer 0Defaults: idle VC timeout 0input/output window sizes 2/2, packet sizes 128/128Timers: T10 60, T11 180, T12 60, T13 60Channels: Incoming-only none, Two-way 1-1024, Outgoing-only noneRESTARTs 1/0 CALLs 0+0/0+0/0+0 DIAGs 0/0LAPB DCE, state CONNECT, modulo 8, k 7, N1 12056, N2 20T1 3000, T2 0, interface outage (partial T3) 0, T4 0VS 7, VR 6, tx NR 6, Remote VR 7, Retransmissions 0Queues: U/S frames 0, I frames 0, unack. 0, reTx 0IFRAMEs 111/118 RNRs 0/0 REJs 0/0 SABM/Es 14/1 FRMRs 0/0 DISCs 0/0The following is sample output from the show x25 context command when the X.25 Failover feature is configured. The "Fail-over delay" field appears when the primary interface has gone down and come back up again. The number of seconds indicates the time remaining until the secondary interface will reset.
Router# show x25 contextSerial1 DLCI 33PROFILE dxe/DCE, address 303
