X.25 Configuration Commands

Use the commands in this chapter to configure Link Access Procedure Balanced (LAPB), X.25, DDN X.25, and Blacker Front-end Encryption (BFE).

LAPB enables you to configure a simple, reliable serial encapsulation method. For historical background and a technical overview of X.25 and LAPB, see the Internetworking Technology Overview publication. For X.25 and LAPB configuration information and examples, refer to the "Configuring LAPB and X.25" chapter in the Access and Communication Servers Configuration Guide.

access-class

To configure an incoming access class on virtual terminals, use the access-class line configuration command.

Syntax Description

Default

No incoming access class is defined.

Command Mode

Line configuration

Usage Guidelines

The access list number is used for both incoming TCP access and incoming PAD access.

In the case of TCP access, the access server uses the IP access list defined using 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.

Example

The following example configures an incoming access class on virtual terminal line 4.

line vty 4
access-class 4 in

Related Commands

The dagger (⁺) indicates that the command is documented in another chapter of this manual.

access-list⁺
line vty ⁺
x29 access-list

bfe

Use the bfe EXEC command to set the access server to participate in emergency mode or to end participation in emergency mode when your system is configured for x25 bfe-emergency decision and x25 bfe-decision ask.

Syntax Description

Command Mode

EXEC

Example

The following example sets the access server to participate in BFE mode:

bfe enter interface serial 0

Related Commands

encapsulation x25
x25 bfe-decision
x25 bfe-emergency

clear x25-vc

Use the clear x25-vc privileged EXEC command to clear virtual circuits.

Syntax Description

Command Mode

Privileged EXEC

Usage Guidelines

This command without any arguments clears all X.25 virtual circuits at once.

Example

The following example clears all virtual circuits:

clear x25-vc

Related Command

x25 idle

encapsulation lapb

To exchange datagrams over a serial interface using LAPB encapsulation, use the encapsulation lapb interface configuration command.

Syntax Description

Default

The default serial encapsulation is HDLC. You must explicitly configure a LAPB encapsulation method.

DTE operation is the default LAPB mode. IP is the default protocol.

Command Mode

Interface configuration

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 x25 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 and the other end a logical DTE. (This assignment is independent of the interface's hardware DTE/DCE identity.)

Both ends of the LAPB link must specify the same protocol encapsulation.

A single-protocol LAPB encapsulation exchanges datagrams of the given protocol, each in a separate LAPB information frame. You should 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 single-protocol interface. It also exchanges datagrams, each in a separate LAPB information frame, although two bytes of protocol identification data precede the protocol data. You should configure the interface with all of the protocol-specific parameters needed for each protocol carried.

Example

The following example sets the operating mode as DTE and specifies that IPX protocol traffic will be carried on the LAPB line:

interface serial 3
encapsulation lapb dte ipx

encapsulation x25

To specify an interface's operation as an X.25 device, use the encapsulation x25 interface configuration command.

Syntax Description

Default

The default serial encapsulation is 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 Mode

Interface configuration

Usage Guidelines

One end of an X.25 link must be a logical DCE and the other end a logical DTE. (This assignment is independent of the interface's hardware DTE/DCE identity.) Typically, when connecting to a public data network (PDN), the customer equipment acts as the DTE and the PDN attachment acts as the DCE.

Cisco has supported the encapsulation of a number of datagram protocols for quite some time, using a standard means when available and 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 configured, that standard will be used unless Cisco's traditional method is explicitly configured. For details see the x25 map command.

When an X.25 interface is reconfigured, all of the interface's X.25 parameters are initialized except the x25 map commands. The x25 map statements that are configured for an interface are not deleted when the encapsulation is changed, so they will be retained if the interface is later reconfigured for X.25 operation.

A access server attaching to the Defense Data Network (DDN) or to a Blacker Front End (BFE) device can be configured to use their respective algorithms to convert between IP and X.121 addresses by using the ddn or bfe options, respectively. An IP address should be assigned to the interface, from which the algorithm will generate the interface's X.121 address; for proper operation, this X.121 address should not be modified.

A access server 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.

Example

The following example configures the interface for connection to a Blacker Front End device.

interface serial 0
encapsulation x25 bfe

lapb hold-queue

Use the lapb hold-queue interface configuration command to define the number of packets to be held until they can be sent over the LAPB connection. Use the no form of the command without an argument to remove this command from the configuration file and return to the default value.

Syntax Description

Default

12 packets

Command Mode

Interface configuration

Example

The following example sets the X.25 hold queue to hold 25 packets:

interface serial 0
lapb hold-queue 25

lapb interface-outage

To specify a period during which a link will remain connected, even if a brief hardware outage occurs, use the lapb interface-outage interface configuration command.

Syntax Description

Defaults

0 milliseconds, which disables this feature.

Command Mode

Interface configuration

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 to be down and, when it is restored, a link set up will be initiated.

Example

The following example sets the interface outage period to 100 milliseconds. The link will remain connected for outages equal to or shorter than that period.

encapsulation lapb dte ip
lapb interface-outage 100

lapb k

To specify the maximum permissible number of outstanding frames, called the window size, use the lapb k interface configuration command.

Syntax Description

Default

7 frames

Command Mode

Interface configuration

Usage Guidelines

If the window size is changed while the protocol is up, the new value will take effect only when the protocol is reset. The operator will be informed that the new value will not take effect immediately.

When using the LAPB modulo 128 mode (extended mode), the window parameter k should be increased to make use of the ability to send a larger number of frames before acknowledgment is required. This is the basis for its ability to achieve greater throughput on high-speed links that have a low error rate.

This configured value should match the value configured in the peer X.25 switch. Nonmatching values will cause repeated LAPB REJ frames.

Example

The following example sets the LAPB window size (the k parameter) to ten frames:

interface serial 0
lapb modulo
lapb k 10

lapb modulo

To specify the LAPB basic (modulo 8) or extended (modulo 128) protocol mode, use the lapb modulo interface configuration command.

Syntax Description

Default

Modulo 8

Command Mode

Interface configuration

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 layer modulo is independent of the LAPB layer modulo. Both ends of a link must use the same LAPB mode.

When using modulo 128 mode, the window parameter k should be increased to make use of the ability to send a larger number of frames before acknowledgment is required. This is the basis for its 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 will take effect only when the protocol is reset. The operator will be informed that the new value will not take effect immediately.

Example

The following example configures a high-speed X.25 link to use LAPB's extended mode:

interface serial 1
encapsulation x25
lapb modulo 128
lapb k 40
clock rate 2000000

Related Command

lapb k

lapb n1

Use the lapb n1 interface configuration command to specify the maximum number of bits a frame can hold (the LAPB N1 parameter).

Syntax Description

Default

12056 bits (1500 bytes)

Command Mode

Interface configuration

Usage Guidelines

It is not necessary to set N1 to an exact value to support a particular X.25 data packet size, although both ends of a connection should have the same N1 value. The N1 parameter serves to avoid processing of any huge frames that result from a "jabbering" interface, an unlikely event.

The Cisco N1 default value corresponds to the hardware interface buffer size. Any changes to this value must allow for an X.25 data packet and LAPB frame overhead. The software supports an X.25 data packet with a maximum packet size plus 3 or 4 bytes of overhead for modulo 8 or 128 operation, respectively, and LAPB frame overhead of 2 bytes of header for modulo 8 operation plus 2 bytes of CRC.

In addition, the various standards organizations specify that N1 be given in bits rather than bytes. While some equipment can be configured using bytes or by automatically adjusting for some of the overhead information present, Cisco devices are configured using the true value of N1.

Table 8-1 specifies the minimum N1 values needed to support a given X.25 data packet. Note that N1 cannot be set to a value less than what is required to support an X.25 data packet size of 128 bytes under modulo 128 operation. This is because all X.25 implementations must be able to support
128-byte data packets.

Example

The following example sets the N1 bits to 9600:

interface serial 0
lapb n1 9600

lapb n2

Use the lapb n2 interface configuration command to specify the maximum number of times a data frame can be transmitted (the LAPB N2 parameter).

Syntax Description

Default

20 retransmissions

Command Mode

Interface configuration

Example

The following example sets the N2 retries to 50:

interface serial 0
lapb n2 50

lapb protocol

Use the lapb protocol interface configuration command to configure a protocol on the LAPB line.

Syntax Description

Default

IP

Command Mode

Interface configuration

Example

The following example sets IP as the protocol on the LAPB line:

interface serial 1
lapb protocol ip

Related Commands

encapsulation lapb

lapb t1

Use the lapb t1 interface configuration command to set the limit retransmission timer period (the LAPB T1 parameter).

Syntax Description

Default

3000 milliseconds

Command Mode

Interface configuration

Usage Guidelines

The retransmission timer determines how long a transmitted frame can remain unacknowledged before the LAPB software polls for an acknowledgment.

To determine an optimal value for the retransmission timer, use the privileged EXEC command ping 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.

Example

The following example sets the T1 retransmission timer to 20000 milliseconds:

interface serial 0
lapb t1 20000

lapb t4

To set the T4 idle timer, after which the system sends out a Poll packet to determine whether the link has suffered an unsignaled failure, use the lapb t4 interface configuration command.

Syntax Description

Defaults

0 seconds, which disables the T4 timer feature.

Command Mode

Interface configuration

Usage Guidelines

Any non-zero T4 duration must be greater than T1, the LAPB retransmission timer period.

Example

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 serial0
encapsulation x25
lapb t4 10

Related Command

lapb t1

service pad

Syntax Description

This command has no arguments or keywords.

Default

All PAD commands and associated connections are enabled.

Command Mode

Global configuration

Example

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 pad
Router(config)#x29 ?
% Unrecognized command
Router(config)#exit 
Router#pad ?
% Unrecognized command

If service pad is enabled, the EXEC pad command and access to an X.29 configuration is granted as shown in the following example:

Router#config terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#service pad
Router(config)#x29 ?
access-list       Define an X.29 access list
inviteclear-time  Wait for response to X.29 Invite Clear message
profile           Create an X.3 profile
Router#pad ?
WORD  X121 address or name of a remote system

Related Commands

x29 access-list
x29 profile

show interfaces serial

Use the show interfaces serial EXEC command to display information about a serial interface.

Syntax Description

Command Mode

EXEC

Sample Displays

The following is sample output from the show interfaces serial command for a serial interface using LAPB encapsulation:

router# show interfaces serial 1
LAPB state is SABMSENT, T1 3000, N1 12056, N2 20, K7, 
VS 0, VR 0, RCNT 0, Remote VR 0, Retransmissions 2
IFRAMEs 0/0 RNRs 0/0 REJs 0/0 SABMs 3/0 FRMRs 0/0 DISCs 0/0
LAPB state is DISCONNECT, T1 3000, N1 12000, N2 20, K7, TH 3000
Window is closed
IFRAMEs 12/28 RNRs 0/1 REJs 13/1 SABMs 1/13 FRMRs 3/0 DISCs 0/11

Table 8-2 shows the fields relevant to all LAPB connections.

The following is sample output from the show interfaces serial command for a serial X.25 interface:

router# show interfaces serial 1
X25 address 000000010100, state R1, modulo 8, idle 0, timer 0, nvc 1
  Window size: input 2, output 2, Packet size: input 128, output 128
  Timers: T20 180, T21 200, T22 180, T23 180, TH 0
  (configuration on RESTART: modulo 8,
  Window size: input 2 output 2, Packet size: input 128, output 128
  Channels: Incoming-only none, Two-way 5-1024, Outgoing-only none)
  RESTARTs 3/2 CALLs 1000+2/1294+190/0+0/ DIAGs 0/0

The stability of the X.25 protocol requires that some parameters not be changed without a RESTART of the protocol. Any change to these parameters will be held until a RESTART is sent or received. If any of these parameters will change, the configuration on RESTART information will be output as well as the values that are currently in effect.

Table 8-3 describes significant fields shown in the display.

show x25 map

To display information about configured address maps, use the show x25 map EXEC command.

Syntax Description

This command has no arguments or keywords.

Command Mode

EXEC

Usage Guidelines

The show x25 map command shows information about the following:

• Configured maps (defined by the x25 map command)

• Maps implicitly defined by encapsulation PVCs (defined by the x25 pvc command)

• Dynamic maps (from the X.25 DDN or BFE operations)

• Temporary maps (from unconfigured CMNS endpoints)

Sample Display

The following is sample output from the show x25 map command:

router# show x25 map
Serial0: X.121 1311001 <--> ip 131.108.170.1
  PERMANENT, BROADCAST, 2 VCS: 3 4*
Serial0: X.121 1311005 <--> ipx 128.1
  PERMANENT

The display shows that two maps have been configured for the Serial0 interface.

Table 8-4 describes significant fields shown in the output displayed.

show x25 remote-red

Use the show x25 remote-red EXEC command to display the one-to-one mapping of the host IP addresses and the remote BFE device's IP addresses.

Syntax Description

This command has no arguments or keywords.

Command Mode

EXEC

Sample Display

The following is sample output from the show x25 remote-red command:

router# show x25 remote-red
Entry	       REMOTE-RED	     REMOTE-BLACK	   INTERFACE
1	           21.0.0.3	       21.0.0.7	       serial3	
2           	21.0.0.10	      21.0.0.6	       serial1
3           	21.0.0.24	      21.0.0.8	       serial3

Table 8-5 describes significant fields shown in the display.

show x25 vc

To display information about active switched virtual circuits (SVCs) and permanent virtual circuits (PVCs), use the show x25 vc EXEC command.

Syntax Description

Command Mode

EXEC

Usage Guidelines

To examine a particular virtual circuit, add an LCN argument to the show x25 vc command.

This command displays information about virtual circuits that are used for any of the following:

• Encapsulation traffic

• Locally switched traffic

• Remotely switched traffic

• CMNS switched traffic

The connectivity information displayed will vary according to the traffic carried by the virtual circuit. For multiprotocol circuits, the output varies depending on the number and identity of the protocols mapped to the X.121 address and the encapsulation method selected for the circuit.

Sample Displays

This section provides three sample displays, which correspond to the four types of traffic information this command displays, and tables that describe the fields in each display.

The following sample display shows a virtual circuit that is being used to encapsulate traffic between the access server and a remote host:

router# show x25 vc 1024
SVC 1024,  State: D1,  Interface: Serial0
Started 0:00:31, last input 0:00:31, output 0:00:31
Connects 170090 <-->
compressedtcp 131.108.170.90
ip 131.108.170.90
multiprotocol cud pid, standard Tx data PID, Reverse charged
Window size input: 2, output: 2
Packet size input: 128, output: 128
PS: 5  PR: 5  ACK: 4  Remote PR: 5  RCNT: 1  RNR: FALSE
Window is closed
Retransmits: 0  Timer (secs): 0  Reassembly (bytes): 0
Held Fragments/Packets: 0/0
Bytes 505/505 Packets 5/5 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0

Table 8-6 describes the general fields shown in the output; Table 8-7 describes the fields specific to encapsulation virtual circuits shown in the output.

Table 8-7 describes the connection description fields for virtual circuits carrying encapsulation traffic.

router# show x25 vc
PVC 1,  State: D1,  Interface: Serial2
 Started 0:01:26, last input never, output never
 PVC <--> Serial1 PVC 1 connected
 Window size input: 2, output: 2
 Packet size input: 128, output: 128
 PS: 0  PR: 0  ACK: 0  Remote PR: 0  RCNT: 0  RNR: FALSE
 Retransmits: 0  Timer (secs): 0  Reassembly (bytes): 0
 Held Fragments/Packets: 0/0
 Bytes 0/0 Packets 0/0 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0
 SVC 5,  State: D1,  Interface: Serial2
  Started 0:00:16, last input 0:00:15, output 0:00:15
  Connects 170093 <--> 170090 from Serial1 VC 5
  Window size input: 2, output: 2
  Packet size input: 128, output: 128
  PS: 5  PR: 5  ACK: 4  Remote PR: 5  RCNT: 1  RNR: FALSE
  Retransmits: 0  Timer (secs): 0  Reassembly (bytes): 0
  Held Fragments/Packets: 0/0
  Bytes 505/505 Packets 5/5 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0

Table 8-8 lists the connection description fields for virtual circuits carrying locally switched X.25 traffic.

router# show x25 vc
PVC 2,  State: D1,  Interface: Serial2
 Started 0:01:25, last input never, output never
 PVC <--> [131.108.165.92] Serial2/0 PVC 1 connected
 XOT between 131.108.165.91, 1998 and 131.108.165.92, 27801
 Window size input: 2, output: 2
 Packet size input: 128, output: 128
 PS: 0  PR: 0  ACK: 0  Remote PR: 0  RCNT: 0  RNR: FALSE
 Retransmits: 0  Timer (secs): 0  Reassembly (bytes): 0
 Held Fragments/Packets: 0/0
 Bytes 0/0 Packets 0/0 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0
SVC 6,  State: D1,  Interface: Serial2
 Started 0:00:04, last input 0:00:04, output 0:00:04
 Connects 170093 <--> 170090 from
 XOT between 131.108.165.91, 1998 and 131.108.165.92, 27896
 Window size input: 2, output: 2
 Packet size input: 128, output: 128
 PS: 5  PR: 5  ACK: 4  Remote PR: 5  RCNT: 1  RNR: FALSE
 Retransmits: 0  Timer (secs): 0  Reassembly (bytes): 0
 Held Fragments/Packets: 0/0
 Bytes 505/505 Packets 5/5 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0

Table 8-9 lists the connection description fields for virtual circuits carrying remotely switched X.25 traffic.

Table 8-10 lists the PVC states that can be reported. These states are also reported by the debug x25 command in PVC-SETUP packets (for remote PVCs only) as well as in the PVCBAD system error message. Some states apply only to remotely switched PVCs.

x25 accept-reverse

Use the x25 accept-reverse interface configuration command to instruct the access server to accept all reverse charge calls. Use the no form of the command to disable this facility.

Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

This command causes the interface to accept reverse charge calls by default. This behavior also can be configured on a per-peer basis using the x25 map interface configuration command.

Example

The following example sets acceptance of reverse charge calls:

interface serial 0
x25 accept-reverse

Related Command

x25 map

x25 address

Use the x25 address interface configuration command to set the X.121 address of a particular network interface.

Syntax Description

Default

No X.121 address is assigned.

Command Mode

Interface configuration

Example

The following example sets the X.121 address for the interface:

interface serial 0
x25 address 00000123005

The address must match that assigned by the X.25 network service provider.

x25 bfe-decision

Use the x25 bfe-decision interface configuration command to direct how a access server configured for x25 bfe-emergency decision will participate in emergency mode.

Syntax Description

Default

no

Command Mode

Interface configuration

Example

The following example shows how to configure serial interface 0 to require an EXEC command from the administrator before it participates in emergency mode. The host IP address is 21.0.0.12, and the address of the remote BFE unit is 21.0.0.1. When the BFE enters emergency mode, the access server will prompt the administrator for EXEC command bfe enter to direct the access server to participate in emergency mode.

interface serial 0
x25 bfe-emergency decision
x25 remote-red 172.30.0.12 remote-black 172.30.0.1
x25 bfe-decision ask

Related Commands

bfe
show x25 remote-red
x25 bfe-emergency

x25 bfe-emergency

Use the x25 bfe-emergency interface configuration command to configure the circumstances under which the access server participates in emergency mode.

Syntax Description

Default

never

Command Mode

Interface configuration

Example

The following example shows how to configure serial interface 0 to require an EXEC command from the administrator before it participates in emergency mode. The host IP address is 172.30.0.12, and the address of the remote BFE unit is 172.30.0.1. When the BFE enters emergency mode, the access server will prompt the administrator for EXEC command bfe enter to direct the access server to participate in emergency mode.

interface serial 0
x25 bfe-emergency decision
x25 remote-red 172.30.0.12 remote-black 172.30.0.1
x25 bfe-decision ask

Related Commands

bfe
x25 bfe-decision

x25 default

Use the x25 default interface configuration command to set a default protocol. Use the no form of the command to remove the protocol specified.

Syntax Description

Default

No protocol is set.

Command Mode

Interface configuration

Usage Guidelines

This command specifies the protocol assumed by the access server to interpret incoming calls with unknown Call User Data. If you do not use the x25 default interface configuration command, the access server clears any incoming calls with unknown Call User Data.

Example

The following example establishes IP as the default protocol for X.25 calls:

interface serial 0
x25 default ip

Related Command

x25 map

x25 facility

Syntax Description

Default

No facility is sent.

Command Mode

Interface configuration

Examples

The following example specifies a transit delay value in an X.25 configuration:

interface serial 0
x25 facility transit-delay 24000

The following example specifies an RPOA name and then send the list via the X.25 user facilities:

x25 rpoa green_list 23 35 36
interface serial 0
x25 facility rpoa green_list
x25 map ip 172.30.170.26 10 rpoa green_list

Related Command

x25 rpoa

x25 hic

Syntax Description

Default

0

Command Mode

Interface configuration

Usage Guidelines

This command is applicable only if you have the X.25 switch configured for incoming only. Incoming is from the perspective of the X.25 DTE. If you do not want any outgoing calls from your DCE, configure the lic and hic values and set the ltc and htc values to 0.

Example

The following example sets a valid incoming-only virtual circuit range of 1 to 5:

interface serial 0
x25 lic 1
x25 hic 5
x25 ltc 6

Related Command

x25 lic

x25 hoc

Syntax Description

Default

0

Command Mode

Interface configuration

Usage Guidelines

This command is applicable only if you have the X.25 switch configured for outgoing only. Outgoing is from the perspective of the X.25 DTE. If you do not want any incoming calls from your DTE, configure the loc and hoc values and set the ltc and htc values to 0.

Example

The following example sets a valid outgoing-only virtual circuit range of 2000 to 2005:

interface serial 0
x25 loc 2000
x25 hoc 2005

Related Command

x25 loc

x25 hold-queue

Use the x25 hold-queue interface configuration command to modify the maximum number of packets that can be held until a virtual circuit is able to transmit. Use the no form of the command without an argument to remove this command from the configuration file and restore the default value.

Syntax Description

Default

10 packets

Command Mode

Interface configuration

Usage Guidelines

If you set the queue-size to 0 when using the no x25 hold-queue command, there will be no hold queue limit. An unlimited hold queue might be appropriate if the interface is configured with a maximum transmission unit (MTU) and IP MTU larger than the X.25 input packet size and X.25 output packet size. If you have configured an MTU and IP MTU larger than these packet sizes, our X.25 software will fragment the encapsulated IP packet into multiple X.25 frames. This fragmentation might cause the X.25 window to close and the hold queue to become full.

Example

The following example sets the X.25 hold queue to hold 25 packets:

interface serial 0
x25 hold-queue 25

Related Commands

A dagger (⁺) indicates that the command is documented in another chapter.

ip mtu ⁺
x25 ips
x25 ops

x25 hold-vc-timer

Use the x25 hold-vc-timer interface configuration command to prevent overruns on some X.25 switches caused by Call Request packets. This command uses the Ignore Destination timer to prevent additional calls to a destination for a given period of time. Use the no form of the command to restore the default value for the timer.

Syntax Description

Default

0

Command Mode

Interface configuration

Usage Guidelines

Only Call Requests that the access server originates will be held down; routed X.25 Call Requests are not affected by this parameter.

Upon receiving a Clear Request for an outstanding Call Request, the X.25 support code immediately tries another Call Request if it has more traffic to send, and this action might cause overrun problems.

Example

The following example sets the Ignore Destination timer to 3 minutes:

interface serial 0
x25 hold-vc-timer 3

x25 host

Use the x25 host global configuration command to define a static host name-to-address mapping. Use the no form of the command to remove the host name.

Syntax Description

Default

No static host name-to-address mapping is defined.

Command Mode

Global configuration

Examples

The following example specifies a static address mapping:

x25 host Willard 4085551212

The following example removes a static address mapping:

no x25 host Willard

x25 htc

Syntax Description

Default

1024 for X.25 network service interfaces

Command Mode

Interface configuration

Usage Guidelines

This command is applicable if you have the X.25 switch configured for two-way.

Example

The following example sets a valid two-way virtual circuit range of 5 to 25:

interface serial 0
x25 ltc 5
x25 htc 25

Related Command

x25 ltc

x25 idle

The access server can clear a switched virtual circuit (SVC) after a period of inactivity. Use the x25 idle interface configuration command to set this period.

Syntax Description

Default

0 (causes the access server to keep the SVC open indefinitely)

Command Mode

Interface configuration

Usage Guidelines

Both calls originated and terminated by the access server are cleared; switched virtual circuits are not cleared. To clear one or all virtual circuits at once, use the privileged EXEC command clear x25-vc.

Example

The following example sets a 5-minute wait period before an idle circuit is cleared:

interface serial 2
x25 idle 5

Related Command

clear x25-vc

x25 ips

Use the x25 ips interface configuration command to set the interface default maximum input packet size to match those of the network.

Syntax Description

Default

128 bytes

Command Mode

Interface configuration

Usage Guidelines

X.25 network connections have a default maximum input packet size set by the network administrator. Larger packet sizes require less overhead processing. To send a packet larger than the X.25 packet size over an X.25 virtual circuit, a access server must break the packet into two or more X.25 packets with the M-bit ("more data" bit) set. The receiving device collects all packets with the M-bit set and reassembles them.

Example

The following example sets the default maximum packet sizes to 512:

interface serial 1
x25 ips 512
x25 ops 512

Related Command

x25 ops

x25 ip-precedence

Use the x25 ip-precedence interface configuration command to enable the ability to open a new virtual circuit based on the IP Type of Service (TOS) field. Use the no form of the commandto force the access server to ignore the TOS field when opening virtual circuits.

Syntax Description

This command has no arguments or keywords.

Default

The access servers open one virtual circuit for all types of service.

Command Mode

Interface configuration

Usage Guidelines

There is a problem associated with this feature in that some hosts send nonstandard data in the TOS field, thus causing multiple, wasteful virtual circuits to be created.

Example

The following example allows new virtual circuits based on the TOS field:

interface serial 3
x25 ip-precedence

x25 lic

Use the x25 lic interface configuration command to set the lowest incoming-only virtual circuit number.

Syntax Description

Default

0

Command Mode

Interface configuration

Usage Guidelines

This command is applicable only if you have the X.25 switch configured for incoming only. Incoming is from the perspective of the X.25 DTE. If you do not want any outgoing calls from your DCE, configure the lic and hic values and set the ltc and htc values to 0.

This command is applicable if you have the X.25 switch configured for two way virtual circuits.

Example

The following example sets a valid incoming-only virtual circuit range of 1 to 5:

interface serial 0
x25 lic 1
x25 hic 5
x25 ltc 6

Related Command

x25 hic

x25 linkrestart

Use the x25 linkrestart interface configuration command to force a packet-level restart when the link level resets. This command restarts X.25 Level 3 when errors occur in Level 2 (LAPB). Use the no form of the command to disable this function.

Syntax Description

This command has no arguments or keywords.

Default

Forcing packet-level restarts is the default and is necessary for networks that expect this behavior.

Command Mode

Interface configuration

Example

The following example disables the link-level restart:

interface serial 3
no x25 linkrestart

x25 loc

Use the x25 loc interface configuration command to set the lowest outgoing-only virtual circuit number.

Syntax Description

Default

0

Command Mode

Interface configuration

Usage Guidelines

This command is applicable only if you have the X.25 switch configured for outgoing only. Outgoing is from the perspective of the X.25 DTE. If you do not want any incoming calls from your DTE, configure the loc and hoc values and set the ltc and htc values to 0.

Example

The following example sets a valid outgoing-only virtual circuit range of 2000 to 2005:

interface serial 0
x25 loc 2000
x25 hoc 2005

Related Command

x25 hoc

x25 ltc

Syntax Description

Default

1

Command Mode

Interface configuration

Usage Guidelines

This command is applicable if you have the X.25 switch configured for two-way.

Example

The following example sets a valid two-way virtual circuit range of 5 to 25:

interface serial 0
x25 ltc 5
x25 htc 25

Related Command

x25 htc

x25 map

To set up the LAN protocols-to-remote host mapping, use the x25 map interface configuration command. To retract a prior mapping, use the no form of the command with the appropriate network protocol(s) and X.121 address argument.

Syntax Description

Default

No LAN protocol-to-remote host mapping is set up.

Command Mode

Interface configuration

Usage Guidelines

Because no defined protocol can dynamically determine LAN protocol-to-remote host mappings, you must enter all of the information for each host with which the access server may exchange X.25 encapsulated traffic.

Two methods are available to encapsulate traffic, Cisco's long-available encapsulation method and the IETF's standard method (defined in RFC 1356); the latter allows hosts to exchange several protocols over a single virtual circuit. Cisco's encapsulation method is the default (for backward compatibility, unless the interface configuration specified ietf).

When you configure multiprotocol maps, you can specify a maximum of nine protocol and address pairs in an x25 map command. However, you can specify a protocol once only. For example, you can specify the IP protocol and an IP address, but you cannot specify another IP address. If compressedtcp and ip are both specified, the same IP address must be used.

Bridging is supported only using Cisco's traditional encapsulation method. For correct operation, bridging maps must specify the broadcast option.

Because most datagram routing protocols rely on broadcasts or multicasts to send routing information to their neighbors, the broadcast keyword is needed to run such routing protocols over X.25.

Encapsulation maps might also specify that traffic between the two hosts should be compressed, thus increasing the effective bandwidth between them at the expense of memory and computation time. Each compression virtual circuit requires memory and computation resources, so compression should be used with care and monitored to maintain acceptable resource usage and overall access server performance.

OSPF treats a nonbroadcast, multiaccess network such as X.25 much the same way it treats a broadcast network in that it requires selection of a designated access server. In previous releases, this required manual assignment in the OSPF configuration using the neighbor interface router configuration command. When the x25 map command is included in the configuration with the broadcast, and the ip ospf network command (with the broadcast keyword) is configured, there is no need to configure any neighbors manually. OSPF will now run over the X.25 network as a broadcast network. (Refer to the ip ospf network interface command for more detail.)

You can modify the options of an x25 map command by restating the complete set of protocols and addresses specified for the map, followed by the desired options. To delete a map command, you must also specify the complete set of protocols and addresses; the options can be omitted when deleting a map.

Once defined, a map's protocols and addresses cannot be changed; this is because the access server cannot determine whether you want to add to, delete from, or modify an existing map's protocol and address specification (or simply mistyped the command). To change a map's protocol and address specification, you must delete it and create a new map.

A given protocol/address pair cannot be used in more than one map on the same interface.

Examples

The following example maps IP address 172.30.2.5 to X.121 address 000000010300. The broadcast keyword directs any broadcasts sent through this interface to the specified X.121 address.

interface serial 0
x25 map ip 172.30.2.5 000000010300 broadcast

The following example sets an RPOA name to be used when originating connections:

x25 rpoa green_list 23 35 36
interface serial 0
x25 facility rpoa green_list
x25 map ip 172.30.170.26 10 rpoa green_list

The following example specifies a network user identifier (NUID) facility to send on calls originated for the address map:

interface serial 0
x25 map IP 172.30.174.32 2 nudata "Network User ID 35"

Strings can be quoted, but quotation marks are not required unless embedded blanks are present.

Related Commands

A dagger (⁺) indicates that the command is documented in another chapter.

ip ospf network ⁺
show x25 map
x25 compress
x25 map bridge
x25 map cmns
x25 map compressedtcp
x25 rpoa

x25 map compressedtcp

Use the x25 map compressedtcp interface configuration command to map compressed TCP traffic to X.121 addresses. Use the no form of the command to disable TCP header compression for the link.

Syntax Description

Default

No mapping of compressed TCP traffic to X.121 addresses.

Command Mode

Interface configuration

Usage Guidelines

The Call User Data of compressed TCP calls is the single byte 0xD8.

TCP header compression is supported over X.25 links. The implementation of compressed TCP over X.25 uses a virtual circuit to pass the compressed packets. The noncompressed packets use another virtual circuit. The NVC map option cannot be used for TCP header compression, as only one virtual circuit can carry compressed TCP header traffic to a given host.

Example

The following example establishes packet compression on serial interface 4:

interface serial 4
ip tcp header-compression
x25 map compressedtcp 172.30.2.5 000000010300

Related Command

x25 map

x25 modulo

Use the x25 modulo interface configuration command to set the packet numbering modulo.

Syntax Description

Default

8

Command Mode

Interface configuration

Usage Guidelines

X.25 supports flow control with a sliding window sequence count. The window counter restarts at zero upon reaching the upper limit, which is called the window modulus.

Example

The following example sets the window modulus to 128:

interface serial 0
x25 modulo 128

Related Commands

x25 win
x25 wout

x25 nvc

Use the x25 nvc interface configuration command to specify the maximum number of switched virtual circuits (SVCs) that a protocol can have open simultaneously to one host. To increase throughput across networks, you can establish up to eight switched virtual circuits to a host.

Syntax Description

Default

1

Command Mode

Interface configuration

Usage Guidelines

When the windows and output queues of all existing connections to a host are full, a new virtual circuit will be opened to the designated circuit count. If a new connection cannot be opened, the data is dropped.

Example

The following example sets the maximum number of SVCs that can be open simultaneously to 4:

interface serial 0
x25 nvc 4

x25 ops

Use the x25 ops interface configuration command to set the interface default maximum output packet size to match those of the network.

Syntax Description

Default

128 bytes

Command Mode

Interface configuration

Usage Guidelines

X.25 networks use maximum input packet sizes set by the network administration. Larger packet sizes are better because smaller packets require more overhead processing. To send a packet larger than the X.25 packet size over an X.25 virtual circuit, a access server must break the packet into two or more X.25 packets with the M-bit ("more data" bit) set. The receiving device collects all packets with the M-bit set and reassembles them.

Example

The following example sets the default maximum packet sizes to 512:

interface serial 1
x25 ips 512
x25 ops 512

Related Command

x25 ips

x25 pvc (encapsulating)

To establish an encapsulation permanent virtual circuit (PVC), use the encapsulating version of the x25 pvc interface configuration command. To delete the PVC, use the no form of the command with the appropriate channel number.

Syntax Description

Default

No encapsulation PVC is established. The PVC window and maximum packet sizes default to the map values or the interface default values.

Command Mode

Interface configuration

Usage Guidelines

PVCs are not supported for ISO CMNS.

You no longer need to specify a datagram protocol/address mapping before you can set up a PVC; a map is implied from the PVC configuration. Configurations generated by the access server will no longer specify a map for encapsulating PVCs.

An X.121 address must be specified for the PVC, much as is done for an x25 map command, although the address does not appear in the PVC data exchange. When configuring a PVC to carry CLNS traffic, the X.121 address is used as the SNPA to associate the PVC with a CLNS neighbor configuration.

Related Command

x25 map

x25 remote-red

Use the x25 remote-red interface configuration command to set up the table that lists the BFE nodes (host or gateways) to which the access server will send packets.

Syntax Description

Default

No BFE node is set up.

Command Mode

Interface configuration

Usage Guidelines

The table that results from this command provides the address translation information the access server sends to the BFE when it is in emergency mode.

Example

The following example sets up a short table of BFE nodes for serial interface 0:

interface serial 0
x25 remote-red 172.30.9.3 remote-black 172.30.9.13
x25 remote-red 172.30.15.1 remote-black 172.30.15.26

Related Command

x25 bfe-decision

x25 rpoa

Use the x25 rpoa global configuration command to set the packet network carrier. Use the no form of the command to remove the specified name.

Syntax Description

Default

No packet network carrier

Command Mode

Global configuration

Usage Guidelines

This command lists transit RPOAs, referenced by name.

Example

The following example sets an RPOA name and then sends the list via the X.25 user facilities:

x25 rpoa green_list 23 35 36
interface serial 0
x25 facility rpoa green_list
x25 map ip 172.30.170.26 10 rpoa green_list

Related Commands

x25 facility
x25 map

x25 suppress-called-address

Use the x25 suppress-called-address interface configuration command to omit the called address in outgoing calls. Use the no form of the command to reset this command to the default state.

Syntax Description

This command has no arguments or keywords.

Default

The called address is sent by default.

Command Mode

Interface configuration

Usage Guidelines

This command omits the called (destination) X.121 address in Call Request packets and is required for networks that expect only subaddresses in the called address field.

Example

The following example suppresses or omits the called address in Call Request packets:

interface serial 0
x25 suppress-called-address

x25 suppress-calling-address

Use the x25 suppress-calling-address interface configuration command to omit the calling address in outgoing calls. Use the no form of the command to reset this command to the default state.

Syntax Description

This command has no arguments or keywords.

Default

The calling address is sent by default.

Command Mode

Interface configuration

Usage Guidelines

This command omits the calling (source) X.121 address in Call Request packets and is required for networks that expect only subaddresses in the calling address field.

Example

The following example suppresses or omits the calling address in Call Request packets:

interface serial 0
x25 suppress-calling-address

x25 t10

Use the x25 t10 interface configuration command to set the limit for the Restart Request retransmission timer (T10) on DCE devices.

Syntax Description

Default

60 seconds

Command Mode

Interface configuration

Example

The following example sets the T10 timer to 30 seconds:

interface serial 0
x25 t10 30

x25 t11

Use the x25 t11 interface configuration command to set the limit for the Call Request Completion timer (T11) on DCE devices.

Syntax Description

Default

180 seconds

Command Mode

Interface configuration

Example

The following example sets the T11 timer to 90 seconds:

interface serial 0
x25 t11 90

x25 t12

Use the x25 t12 interface configuration command to set the limit for the Reset Request retransmission timer (T12) on DCE devices.

Syntax Description

Default

60 seconds

Command Mode

Interface configuration

Example

The following example sets the T12 timer to 30 seconds:

interface serial 0
x25 t12 30

x25 t13

Use the x25 t13 interface configuration command to set the limit for the Clear Request retransmission timer (T13) on DCE devices.

Syntax Description

Default

60 seconds

Command Mode

Interface configuration

Example

The following example sets the T13 timer to 30 seconds:

interface serial 0
x25 t13 30

x25 t20

Use the x25 t20 interface configuration command to set the limit for the Restart Request retransmission timer (T20) on DTE devices.

Syntax Description

Default

180 seconds

Command Mode

Interface configuration

Example

The following example sets the T20 timer to 90 seconds:

interface serial 0
x25 t20 90

x25 t21

Use the x25 t21 interface configuration command to set the limit for the Call Request Completion timer (T21) on DTE devices.

Syntax Description

Default

200 seconds

Command Mode

Interface configuration

Example

The following example sets the T21 timer to 100 seconds:

interface serial 0
x25 t21 100

x25 t22

Use the x25 t22 interface configuration command to set the limit for the Reset Request retransmission timer (T22) on DTE devices.

Syntax Description

Default

180 seconds

Command Mode

Interface configuration

Example

The following example sets the T22 timer to 90 seconds:

interface serial 0
x25 t22 90

x25 t23

Use the x25 t23 interface configuration command to set the limit for the Clear Request retransmission timer (T23) on DTE devices.

Syntax Description

Default

180 seconds

Command Mode

Interface configuration

Example

The following example sets the T23 timer to 90 seconds:

interface serial 0
x25 t23 90

x25 th

Use the x25 th interface configuration command to instruct the access server to send an acknowledgment packet when it has received a threshold of data packets it has not acknowledged, instead of waiting until its input window is full. This command improves line responsiveness at the expense of bandwidth.

Syntax Description

Default

0 (which disables the delayed acknowledgment strategy)

Command Mode

Interface configuration

Usage Guidelines

The access server sends acknowledgment packets when the number of input packets reaches the count you specify, providing there are no other packets to send. For example, if you specify a count of 1, the access server can send an acknowledgment per input packet.

Example

The following example sends five Receiver Ready acknowledgments per packet as an input packet delay:

interface serial 1
x25 th 5

Related Commands

x25 win
x25 wout

x25 win

Use the x25 win interface configuration command to change the default maximum number of unacknowledged incoming packets for the interface.

Syntax Description

Default

2 packets

Command Mode

Interface configuration

Usage Guidelines

This command determines how many packets the access server can receive before sending an X.25 acknowledgment. To maintain high bandwidth utilization, assign this limit the largest number that the network allows.

Example

The following example specifies that five packets must be received before sending an X.25 acknowledgment:

interface serial 1
x25 win 5

Related Commands

x25 modulo
x25 th
x25 wout

x25 wout

Syntax Description

Default

2 packets

Command Mode

Interface configuration

Usage Guidelines

This command determines the default number of packets the access server can send before waiting for an X.25 acknowledgment. To maintain high bandwidth utilization, assign this limit the largest number that the network allows.

Example

The following example specifies an upper limit of five for the number of outstanding unacknowledged packets for the output window:

interface serial 1
x25 wout 5

Related Commands

x25 modulo
x25 th
x25 win

x29 access-list

To limit access to the access server from certain X.25 hosts, use the x29 access-list global configuration command. To delete an entire access list, use the no form of this command.

Syntax Description

Default

No access lists are defined.

Command Mode

Global

Usage Guidelines

An access list can contain any number of access list items. The list are processed in the order in which you entered them, with the first match causing the permit or deny condition. If an X.121 address does not match any of the regular expression in the access list, access will be denied.

Access lists take advantage of the message field defined by Recommendation X.29, which describes procedures for exchanging data between two PADs or a PAD and a DTE device.

The UNIX-style regular expression characters allow for pattern matching of characters and character strings in the address. Various pattern-matching constructions are available that will allow many addresses to be matched by a single regular expressions. Refer to the "Regular Expressions" appendix in this manual for more information.

Example

The following example permits connections to hosts with addresses beginning with the string 31370:

x29 access-list 2 permit ^31370

x29 profile

To create a PAD profile script for use by the translate command, use the x29 profile global configuration command.

Syntax Description

Default

No PAD profile script is created.

Command Mode

Global configuration

Usage Guidelines

When an X.25 connection is established, the access server acts as if an X.29 SET PARAMETER packet had been sent containing the parameters and values set by the x29 profile command and sets the access server accordingly.

Example

The following profile script turns local edit mode on when the connection is made and establishes local echo and line termination upon receipt of a Return. The name "linemode" is used with the translate command to effect use of this script.

x29 profile linemode 2:1 3:2 15:1

Related Command

A dagger (⁺) indicates that the command is documented in another chapter.

translate ⁺