X.25 Enhancements

Description

New X.25 features include the following:

• Cisco's priority queuing and custom queuing are available on X.25 interfaces.

• X.25 service is supported on ISDN BRI D channels.

• The flexible x25 route command offers selection criteria and address modification options for all destinations.

• An optional X.28 user interface is provided for the PAD feature.

• PAD calls can be made over XOT. Previously, the PAD capability was only available for use with a physical X.25 interface.

Platforms

X.25 enhancements run on these Cisco platforms:

• Cisco 1000 series

• Cisco 2500 series

• Cisco 4000 series (Cisco 4000, 4000-M, 4500, 4500-M, 4700, 4700-M)

• Cisco 7000 series

• Cisco 7200 series

• Cisco 7500 series

Configuration Tasks

To configure X.25, complete the tasks in one or more of the following sections, depending upon the X.25 application or task required for your network. The interface, datagram transport, and routing tasks are divided into sections, and the more commonly used features are presented first.

• Configure X.25 Priority Queuing or Custom Queuing

• Configure an X.25 Route

• Define the QLLC XID Value Associated with an X.25 Device

• Open a QLLC Connection to the Local Token Ring Device

• Enable QLLC Conversion on the Appropriate Serial Interfaces

• Monitor and Maintain X.25 Circuits

Configure X.25 Priority Queuing or Custom Queuing

Two added types of output queuing are available for X.25:

• Priority queuing--Classifies packets based on certain criteria and then assigns the packets to one of four output queues, with high, medium, normal, or low priority.

• Custom queuing--Classifies packets, assigns them to one of 16 output queues, and controls the percentage of an interface's available bandwidth that is used for a queue.

Understand the Effect of X.25 Flow Control on Queuing

Output queuing for X.25 interfaces differs subtly from its use with other protocols because X.25 is a strongly flow-controlled protocol. Each X.25 virtual circuit has an authorized number of packets it can send before it must suspend transmission to await acknowledgment of one or more of the packets that were sent.

Queue processing is also subject to a virtual circuit's ability to send data; a high priority packet on a virtual circuit that cannot send data will not stop other packets from being sent if they are queued for a virtual circuit that can send data. In addition, a datagram that is in the process of being fragmented and sent may have its priority artificially promoted if higher priority traffic is blocked by the fragmentation operation.

Configure Queuing

Both priority queuing and custom queuing can be defined, but only one method can be active on a given interface.

To configure priority queuing and custom queuing for X.25, perform the following tasks:

Step 1 Perform the standard priority and custom queuing tasks except the task of assigning a priority or custom group to the interface, as described in the "Managing the System" chapter in the Cisco IOS Release 11.2 Configuration Fundamentals Configuration Guide.

Step 2 Perform the standard X.25 encapsulation tasks, as specified in the "Configure an X.25 Datagram Transport" in the Cisco IOS Release 11.2 Wide-Area Networking Configuration Guide.

Step 3 Assign either a priority group or a custom queue to the interface, as described in the "Managing the System" chapter in the Cisco IOS Release 11.2 Configuration Fundamentals Configuration Guide.

Configure an X.25 Route

An X.25 route table permits you to control which destination is selected for several applications. When an X.25 service receives a call that must be forwarded, the X.25 route table determines which X.25 service (X.25, CMNS or XOT) and destination should be used. When a PAD call is originated by the router, either from a user request or a protocol translation event, the route table similarly determines what X.25 service and destination should be used.

You create the X.25 route table and add route entries to it. You can optionally specify the entry's order in the table, the criteria to match against the virtual circuit information, and whether to modify the destination or source addresses. Each entry must specify the disposition of the virtual circuit (that is, what is done with the virtual circuit). Each route can also specify XOT keepalive options.

The route table is used as follows:

• Virtual circuit information is matched against selection criteria specified for each route.

• The table is scanned sequentially from the top.

• The first matching route determines how the virtual circuit is handled.

• Once a matching entry is found, the call addresses can be modified and the call is disposed of (forwarded or cleared) as instructed by the entry.

Each application can define special conditions if a route will not be used or what occurs if no route matches. For instance, switched X.25 will skip a route if the disposition interface is down and clear a call if no route matches.

To configure an X.25 route (thus adding the route to the X.25 routing table), perform the following task in global configuration mode:

Several options offer versatility and flexibility when you use the x25 route command:

• #position --Position in the table. You can use the optional #position element to indicate the number of the entry in the route able. For example, #9 indicates the ninth entry from the top. The route table is always searched sequentially from the top, and the first match found will be used.

• selection--Criteria to define which virtual circuits the route will apply to. You can match against zero to four of the following optional selection elements:

  • destination-pattern

  • source source-pattern

  • dest-ext nsap-destination-pattern

  • cud user-data-pattern

• modification --Modifications to the source or destination address for address translation. You can use none, one, or both of the following optional modification elements to change the source or destination address before forwarding the call to the destination:

  • substitute-source rewrite-source

  • substitute-dest rewrite-destination

• disposition--Where the virtual circuit will be forwarded or whether it will be cleared. You are required to use one of the following disposition elements:

  • interface serial-interface

  A route to a specific serial-interface will send the virtual circuit to an X.25 service on a synchronous serial interface.
  

  • interface cmns-interface mac mac-address

  A route to a broadcast interface will send the virtual circuit to a CMNS partner reachable on a broadcast medium at a specified MAC address. The CMNS interface can be an Ethernet, Token Ring, or FDDI interface.
  

  • xot ip-address [ip2-address [...[ip6-address]]] [xot-source interface]

  A route to an xot destination (formerly called a remote or tunneled configuration) will send the virtual circuit to the XOT service for establishment of a TCP connection across which the XOT virtual circuit packets will travel. An xot disposition may specify alternate destinations to try if a TCP connection cannot be established for all preceding destinations.
  

  • clear

  A route to a clear destination will deny further service to the virtual circuit by shutting down the connection.
  

• xot-keepalive --options. You can use none, one, or both of the following optional xot-keepalive elements:

  • xot-keepalive-period seconds

  • xot-keepalive-tries count

Enable QLLC Conversion on the Appropriate Serial Interfaces

Qualified Logical Link Control (QLLC) is IBM's protocol that transports SNA terminal traffic over an X.25 network.

You can enable QLLC conversion on a serial interface to support either a switched virtual circuit (SVC) or a permanent virtual circuit (PVC). The tasks you perform differ somewhat depending on the type of virtual circuit you plan to support on the interface. In either case, first verify that RSRB is enabled by performing the following task in privileged EXEC mode:

In the sections for the appropriate serial interfaces of the show configuration display, look for one or more source-bridge remote-peer entries and a source-bridge ring-number entry.

To enable QLLC conversion to support an SVC, perform the following tasks in interface configuration mode:

To enable QLLC conversion to support a PVC, perform the following tasks in interface configuration mode:

To configure QLLC to accept a call from any remote X.25 device, perform the following task in interface configuration mode:

In a Token Ring or RSRB environment, the LAN-attached devices initiate a connection by sending a null XID packet upstream. If the Cisco IOS software forwards this null XID to an X.25-attached FEP, the FEP responds as if it were connecting to a PU2.1 device, and breaks the connection when the PU 2.0 next sends an XID Format 0 Type 2. To resolve this situation and to enable the connection, perform the following task in interface configuration mode:

The qllc npsi-poll command intercepts any null XID packet that the router receives on the LAN interface and returns a null XID response to the downstream device. It continues to allow XID Format 3 and XID Format 0 packets through the X.25 device.

Define the QLLC XID Value Associated with an X.25 Device

The exchange identification (XID) serves as a password to ensure that only those devices that should communicate with the Token Ring host have that privilege. If the XID is defined in NCP on the host, you must enable the Cisco IOS software to reply (on behalf of the X.25 device) to the Token Ring host's requests for an XID reply. Although the XID value is used to reply to XID requests received on the LLC2 side of the connection, apply this command on the serial interface defined for X.25. This XID value must match that of IDBLK and IDNUM defined in the NCP.

To define the XID value associated with an X.25 device, perform the following task in interface configuration mode:

Open a QLLC Connection to the Local Token Ring Device

If you plan to use SVCs rather than PVCs, you must enable the Cisco IOS software to open a connection to the local Token Ring device on behalf of the remote X.25 device when an incoming call is received. When data conversion is used over an SVC, the remote X.25 device typically initiates the X.25/QLLC session, and the software in turn initiates the LLC2 session.

To enable the software to open a connection to the local Token Ring device, perform the following task in interface configuration mode:

Monitor and Maintain X.25 Circuits

Perform the following tasks to monitor and maintain X.25 circuits:

Configuration Examples

The following example prevents X.25 routing for calls that do not specify a source address:

x25 route source ^$ clear

The following example configures alternate XOT hosts for the routing entry. If the first address listed is not available, subsequent addresses are tried until a connection is made. If no connection can be formed, the call is cleared.

x25 route ^3106$ xot 172.20.2.5 172.20.7.10 172.10.7.9

For an extensive series of X.25 routing examples, see the x25 route command in this document.

Command Reference

This section documents new and modified commands. All other commands used with this feature are documented in the Cisco IOS Release 11.2 command references.

• clear x25

• clear xot

• qllc accept-all-calls

• show x25 interface

• show x25 services

• show x25 vc

• show x25 xot

• x25 alias

• x25 pvc qllc

• x25 route

The following commands have been replaced by commands documented in this chapter:

• x25 map cmns

• x25 route alias

clear x25

Use the clear x25 privileged EXEC command to restart an X.25 or CMNS service, to clear an SVC, or to reset a PVC.

Syntax Description

Command Mode

Privileged EXEC

Usage Guidelines

This command first appeared in Cisco IOS Release 11.2 F. (This command replaces the clear x25-vc command, which first appeared in Cisco IOS Release 8.3.)

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.

Examples

The following command clears the SVC or resets the PVC specified:

clear x25 serial 0 1

The following command forces an X.25 restart, which implicitly clears all SVCs and resets all PVCs using the interface:

clear x25 serial 0

The following command restarts the specified CMNS service (if active), which implicitly clears all SVCs using the service:

clear x25 ethernet 0 0001.0002.0003

Related Commands

clear xot
show x25 services

clear xot

To clear an XOT SVC or reset an XOT PVC, use the clear xot EXEC command.

Syntax Description

Command Mode

EXEC

Usage Guidelines

This command first appeared in Cisco IOS Release 11.2 F.

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.

Example

The following command will clear or reset, respectively, the SVC or PVC using the TCP connection identified:

clear xot remote 1.1.1.1 1998 local 2.2.2.2 2000

Related Command

show x25 services

qllc accept-all-calls

Use the qllc accept-all-calls interface configuration command to enable the router to accept a call from any remote X.25 device. Use the no form of this command to cancel the request.

Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 11.2 F.

This command allows QLLC to accept all inbound X.25 calls, provided that the QLLC Call User Data (CUD) is in the call packet and the destination X.121 address in the call packet matches the serial interface's configured destination X.121 address or subaddress. When using this command, the source X.121 address does not need to be configured via an x25 map qllc command for the call to be accepted.

This command is applicable to QLLC support for DLSw+, APPN, and DSPU. It is not applicable to QLLC support for SRB and RSRB.

Example

The following example enables QLLC connectivity for DLSw+ and allows QLLC to accept all inbound X.25 calls. Every X.25 connection request for X.121 address 0308 with QLLC CUD is directed to DLSw+. The first SVC to be established will be mapped to virtual MAC address 4000.0B0B.0001. If a call comes in with an X.121 address of 0308, the call will be forwarded to MAC address 4001.1161.1234.

interface serial 0
encapsulation x25
x25 address 0308
qllc accept-all-calls
qllc dlsw vmac 4000.0B0B.0001 500 partner 4001.1161.1234

Related Command

x25 map qllc

show x25 interface

To display information about VCs that use an X.25 interface and, optionally, about a specified virtual circuit, use the show x25 interface EXEC command.

Syntax Description

Command Mode

EXEC

Usage Guidelines

This command first appeared in Cisco IOS Release 11.2 F.

Example

The following example displays X.25 information about VCs on serial interface 0:

Router# show x25 interface serial 0
SVC 1,  State: D1,  Interface: Serial0
  Started 00:13:52, last input 00:00:05, output never
  Connects 3334 <-> ip 3.3.3.4
  Call PID ietf, Data PID none
  Window size input: 7, output: 7
  Packet size input: 512, output: 512
  PS: 0  PR: 6  ACK: 1  Remote PR: 0  RCNT: 5  RNR: no
  P/D state timeouts: 0  timer (secs): 0
  data bytes 0/2508 packets 0/54 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0
SVC 32,  State: D1,  Interface: Serial0.11
  Started 00:16:53, last input 00:00:37, output 00:00:28
  Connects 3334 <-> clns
  Call PID cisco, Data PID none
  Window size input: 7, output: 7
  Packet size input: 512, output: 512
  PS: 5  PR: 4  ACK: 4  Remote PR: 4  RCNT: 0  RNR: no
  P/D state timeouts: 0  timer (secs): 0
  data bytes 378/360 packets 21/20 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0

show x25 services

To display information pertaining to the X.25 services, use the show x25 services EXEC command.

Syntax Description

This command has no arguments and keywords.

Command Mode

EXEC

Usage Guidelines

This command first appeared in Cisco IOS Release 11.2 F.

This command is the default form of the show x25 command.

Example

The following example displays information about X.25 services:

Router# show x25 services
X.25 software, Version 3.0.0.
  3 configurations supporting 3 active contexts
  VCs allocated, freed and in use: 7 - 0 = 7
  VCs active and idle: 4, 3
XOT software, Version 2.0.0.
  VCs allocated, freed and in use: 2 - 1 = 1
  connections in-progress: 0 outgoing and 0 incoming
  active VCs: 1, connected to 1 remote hosts

Related Commands

show x25 interface
show x25 map
show x25 route
show x25 vc

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

This command first appeared in Cisco IOS Release 8.3.

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

This command displays information about virtual circuits. Virtual circuits may be used for a number of purposes, such as the following:

• Encapsulation traffic

• Traffic switched between X.25 services (X.25, CMNS and XOT)

• PAD traffic

• QLLC 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 Display for Encapsulated Traffic

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 172.20.170.90
    ip 172.20.170.90
 Call PID multi, Data PID ietf
 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
 P/D state timeouts: 0 Timer (secs): 0
  data bytes 505/505 packets 5/5 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0

Table 24 describes the fields shown in the sample output that are typical for virtual circuits.

Table 25 describes the connection fields specific for encapsulation traffic.

Sample Display for Locally Switched X.25 Traffic

The following is sample output from the show x25 vc command used on a virtual circuit carrying locally switched X.25 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
  P/D state timeouts: 0 Timer (secs): 0 
  data 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
  P/D state timeouts: 0 Timer (secs): 0 
  data bytes 505/505 packets 5/5 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0

Table 26 describes the connection fields for virtual circuits carrying locally switched X.25 traffic.

Sample Display for Locally Switched X.25 Traffic Between PVCs and SVCs

The following is sample output from the show x25 vc command used on a virtual circuit carrying locally switched PVC to SVC X.25 traffic:

Router# show x25 vc
PVC 5,  State: D1,  Interface: Serial0
  Started 4d21h, last input 00:00:14, output 00:00:14
  Connects 101600 <--> 201700 from Serial2 VC 700
  D-bit permitted
  Window size input: 2, output: 2
  Packet size input: 128, output: 128
  PS: 5  PR: 5  ACK: 4  Remote PR: 5  RCNT: 1  RNR: no
  P/D state timeouts: 0  timer (secs): 0
  data bytes 1000/1000 packets 10/10 Resets 1/0 RNRs 0/0 REJs 0/0 INTs 0/0
SVC 700,  State: D1,  Interface: Serial2
  Started 00:00:16, last input 00:00:16, output 00:00:16
  Connects 101600 <--> 201700 from Serial0 PVC 5
  Window size input: 2, output: 2
  Packet size input: 128, output: 128
  PS: 5  PR: 5  ACK: 5  Remote PR: 4  RCNT: 0  RNR: no
  P/D state timeouts: 0  timer (secs): 103
  data bytes 500/500 packets 5/5 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0

Table 27 describes the connection fields for virtual circuits carrying locally switched X.25 traffic between PVCs and SVCs.

Sample Display for Remotely Switched X.25 Traffic

The following is sample output from the show x25 vc command used on a virtual circuit carrying remotely switched X.25 traffic:

Router# show x25 vc
PVC 2, State: D1, Interface: Serial2
 Started 0:01:25, last input never, output never
 PVC <--> [172.20.165.92] Serial2/0 PVC 1 connected
 XOT between 171.20.165.91, 1998 and 172.20.165.92, 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
 P/D state timeouts: 0 Timer (secs): 0 Reassembly (bytes): 0
 Held Fragments/Packets: 0/0
 data 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 172.20.165.91, 1998 and 172.20.165.92, 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
 P/D state timeouts: 0 Timer (secs): 0 Reassembly (bytes): 0
 Held Fragments/Packets: 0/0
 data bytes 505/505 packets 5/5 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0

Table 28 describes the connection fields for virtual circuits carrying remotely switched X.25 traffic.

Table 29 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.

show x25 xot

To display information for all XOT virtual circuits that match a given criterion, use the show x25 xot EXEC command.

Syntax Description

Command Mode

EXEC

Usage Guidelines

This command first appeared in Cisco IOS Release 11.2 F.

Example

The following example displays information about all XOT virtual circuits:

Router> show x25 xot
SVC 11,  State: D1,  Interface: [2.2.2.2,1998/2.2.2.1,11002]
  Started 00:00:08, last input 00:00:08, output 00:00:08
  Line: 0   con 0    Location:  Host: 5678
  111 connected to 5678 <--> PAD
  Window size input: 2, output: 2
  Packet size input: 128, output: 128
  PS: 2  PR: 3  ACK: 3  Remote PR: 2  RCNT: 0  RNR: no
  P/D state timeouts: 0  timer (secs): 0
  data bytes 54/18 packets 2/3 Resets 0/0 RNRs 0/0 REJs 0/0 INTs 0/0

Related Commands

show x25 interface
show x25 services

x25 alias

To configure an interface alias address that will allow this interface to accept calls with other destination addresses, use the x25 alias interface configuration command.

Syntax Description

Default

No alias is configured.

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 11.2 F. It replaces the functionality that was provided by the alias keyword of the x25 route command.

Encapsulation, PAD, and QLLC calls are normally accepted when the destination address is that of the interface (or the zero-length address). Those calls will also be accepted when the destination address matches a configured alias.

Example

An X.25 call may be addressed to the receiving interface; calls addressed to the receiving interface are eligible for acceptance as a datagram encapsulation, PAD or QLLC connection, and may not be routed. In the following example, serial interface 0 is configured with a native address of 0000123 and a destination alias for any address that starts with 1111123. That is, serial interface 0 can accept its own calls and calls for any destination that starts with 1111123.

interface serial 0
 encapsulation x25
 x25 address 0000123
 x25 alias ^1111123.*

x25 map cmns

The enhanced x25 route command replaces the x25 map cmns command. Refer to the description of the x25 route command for more information.

x25 pvc qllc

Use the x25 pvc qllc interface configuration command to associate a virtual MAC address with a PVC for communication using QLLC conversion. The no form of this command removes the association.

Syntax Description

Default

No association is made.

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 11.0.

Before a Token Ring SNA device communicates with an X.25-attached SNA device, it sends a request to the QLLC virtual MAC address. The Cisco IOS software accepts this connection request and forwards the data to the appropriate X.25 PVC. The virtual circuit is determined from the LCN configured in the x25 pvc qllc command.

You use the x25 pvc qllc command in conjunction with the qllc srb command.

Example

In the following example, the x25 pvc qllc command associates the virtual MAC address 0100.0000.0001, as defined in the previous x25 map qllc command entry, with PVC 3:

interface serial 0
encapsulation x25
x25 address 31102120100
x25 pvc 3 qllc 0100.0000.0001
qllc srb 0100.0000.0001 103 1000
qllc partner 0100.0000.0001 4001.1161.1234

Related Commands

qllc srb

x25 map qllc

x25 route

To create an entry in the X.25 routing table (to be consulted for forwarding incoming calls and for placing outgoing PAD or protocol translation calls), use an appropriate form of the x25 route global configuration command. To remove an entry from the table, use the no form of the command.

Syntax Description

Default

No entry is created in the X.25 routing table.

Command Mode

Global configuration

Usage Guidelines

The enhanced x25 route command replaces the x25 map cmns command. The x25 route alias form of this command (supported in earlier releases) has been replaced by the x25 alias command.

The selection criteria source and dest-ext first appeared in Cisco IOS Release 11.2 F. The interface disposition to a CMNS destination first appeared in Cisco IOS Release 11.2 F; in prior releases, CMNS routing information was implied by maps defining an NSAP prefix for a CMNS host's MAC address. The clear interface disposition first appeared in Cisco IOS Release 11.2 F; in prior releases, the disposition was implicit in a route to the Null 0 interface. The modification elements are long-standing but newly applicable to all dispositions in Cisco IOS Release 11.2 F.

Selection Options

Selection options specify match criteria. When a call matches all selection criteria in an X.25 route, then the specified modification and disposition are used for the call.

As many as four selection options can be used to determine the route:

• Called X.121 network interface address (destination host address)

• Calling X.121 network interface address (source host address)

• Called address extension (destination NSAP address)

• X.25 packet's call user data (CUD) field

Table 31 lists the selection options for the x25 route command. At least one selection or modification element must be specified in the x25 route command.

Modification Options

Addresses typically need to be modified when traffic from a private network that uses arbitrary X.121 addresses must transit a public data network, which must use its own X.121 addresses. The easiest way to meet the requirement is to specify in the x25 route command a way to modify the private address into a network X.121 address or to modify a network X.121 address into a private address. The addresses are modified so that no change to the private addressing scheme is required.

The modification options use the standard UNIX regular expression substitution operations to change an X.25 field. A pattern match is applied to an address field, which is rewritten as directed by a rewrite pattern.

Table 32 lists the modification options for the x25 route command. At least one selection or modification element must be specified in the x25 route command.

Refer to Table 33, Table 34, and Table 35 for summaries of pattern matching, character matching, and pattern rewrite elements. Note that up to nine pairs of parentheses can be used to identify patterns to be included in the modified string. A more complete description of the pattern-matching characters is found in the "Regular Expressions" appendix in the Cisco IOS Release 11.2 Access Services Command Reference.

Disposition Option

The xot-source disposition option can improve the resilience of the TCP connection if, for instance, a loopback interface is specified. By default, a TCP connection's source IP address is that of the interface used to initiate the connection; a TCP connection will fail if either the source or destination IP address is no longer valid. Because a loopback interface never goes down, its IP address is always valid. Any TCP connections originated using a loopback interface can be maintained as long as a path exists to the destination IP address, which may also be the IP address of a loopback interface.

Table 36 lists the disposition choices for the x25 route command. You are required to select one of these choices.

XOT Keepalive Options

TCP maintains each connection using a keepalive mechanism that starts with a default time period and number of retry attempts. If a received XOT connection is dispatched using a route with explicit keepalive parameters, those values will be used for the TCP connection. If an XOT connection is sent using a route with explicit keepalive parameters, those values will be used for the TCP connection.

Table 37 lists and describes the xot-keepalive options for the x25 route command.

X.25 Routing Action When a Match Is Found

If a matching route is found, the incoming call is forwarded to the next hop depending on the routing entry. If no match is found, the call is cleared. If the route specifies a serial interface running X.25 or a broadcast interface running CMNS, the router attempts to forward the call to that host. If the interface is not operational, the subsequent routes are checked for forwarding to an operational interface. If the interface is operational but out of available virtual circuits, the call is cleared. Otherwise, the expected Clear Request or Call Accepted message is forwarded back toward the originator. A call cannot be forwarded out the interface on which it arrived.

If the matching route specifies an XOT disposition, a TCP connection is established to port 1998 at the specified IP address, which must be an XOT host. The Call Request packet is forwarded to the remote host, which applies its own criteria to handle the call. If, upon receiving an XOT call, a routing table entry is not present, or the destination is unavailable, a Clear Request is sent back and the TCP connection is closed. Otherwise, the call is handled and the expected Clear Request or Call Accepted packet is returned. Incoming calls received via XOT connections that match a routing entry specifying an XOT destination are cleared. This restriction prevents Cisco routers from establishing an XOT connection to another router that would establish yet another XOT connection.

Examples

The following example uses regular expression pattern matching characters to match just the initial portion of the complete X.25 address. Any call with a destination address beginning with 3107 that is received on an interface other than serial 0 is forwarded to serial 0.

x25 route ^3107 interface serial 0

The following example prevents X.25 routing for calls that do not specify a source address:

x25 route source ^$ clear

The following example configures alternate XOT hosts for the routing entry. If the first address listed is not available, subsequent addresses are tried until a connection is made. If no connection can be formed, the call is cleared.

x25 route ^3106$ xot 172.20.2.5 172.20.7.10 172.10.7.9

The following example clears calls that contain a 3 in the source address. The disposition keyword clear is new:

x25 route source 3 clear

The following example clears calls that contain two consecutive 3's in the source address:

x25 route source 33 clear

The following example clears a call to the destination address, 9999:

x25 route ^9999$ clear

The following example specifies a route for specific source and destination addresses. (The ability to combine source and destination patterns is a new feature.)

x25 route ^9999$ source ^333$ interface serial 0

The following example routes the call to the XOT host at the specified IP address. The disposition keyword xot is new. In prior releases the keyword ip was used.

x25 route ^3333$ xot 172.21.53.61

The following example routes calls containing the destination extension address preamble 11.1234:

x25 route dest-ext ^11.1234.* interface serial 0

The following example rewrites the destination address as 9999. There must be a minimum of four 8's in the address. (8888888 will change to 9999.)

x25 route 8888 substitute-dest 9999 interface serial 0

The following example substitutes only part of the destination address. "^88" specifies the original destination string must begin with 88. "(.*)" indicates the string can end with any number, 0-9, and can be more than one digit. "99\1" changes the destination address to 99 plus whatever matches ".*" in the original destination address. For example, 8881 will change to 9981.

x25 route ^88(.*) substitute-dest 99\1 interface serial 0

The following example substitutes only part of the destination address and also removes a specified number of digits from the address. "^88" specifies the original destination string must begin with 88. "(..)" matches any two digits. "(.*)" specifies the string can end with any number, 0-9, and can occur zero or more times. Thus any address that starts with 88 and has four or more digits will be rewritten to start with 99 and omit the third and fourth digits. For example, 881234 will change to 9934.

x25 route ^88(..)(.*) substitute-dest 99\2 interface serial 0

The following example looks for a specified destination address and changes the source address. "9999" is the destination address. The original source address changes to "2222" because the call is made to the destination 9999.

x25 route ^9999$ substitute-source 2222 interface serial 0

The following example rewrites the source address based upon the source address. "9999" matches any destination address with four consecutive 9s. "^...(.*)" matches any source address with at least three digits; the command removes the first three digits and rewrites any digits after the first three as the new source address. For example, a call to 9999 from the source address 77721 will be forwarded using the calling address 21 and the called address 9999.

x25 route 9999 source ^...(.*) substitute-source \1 interface serial 0

The following example adds a digit to the source and destination addresses patterns. "09990" is the destination address pattern. The source can be any address. "9\0" specifies to add a leading 9 to the destination address pattern. "3\0" specifies to add a leading 3 to the source address pattern. For example, a call using source 03330 and destination 09990 will change to 303330 and 909990, respectively.

x25 route 09990 source .* substitute-dest 9\0 substitute-source 3\0 interface serial 0

Related Command

show x25 route

x25 route alias

This command is replaced by the x25 alias command, which is documented in this chapter.

Debug Commands

This section documents the debug x25 command. The X.25 debug command forms are available for the privileged user to monitor service traffic. A range of keywords is available to limit the output to the specific area of interest.

debug x25

To display information about X.25 traffic, use one of the following debug x25 commands. The commands allow you to display all information or an increasingly restrictive part of the information.

Caution  This command is processor intensive and can render the router useless. Use this command only when the aggregate of all reportable X.25 traffic is fewer than five packets per second. The generic forms of this command should be restricted to low-speed, low-usage links running below 19.2 kbps. Because the debug x25 vc command and the debug x25 vc events command display traffic for only a small subset of virtual circuits, they are safer to use under heavy traffic conditions, as long as events for that virtual circuit are fewer than 25 packets per second.

To display information about all X.25 traffic, including traffic for X.25, CMNS, and XOT services, use the debug x25 EXEC command. To disable debugging output, use the no form of this command.

To display information about a specific X.25 service class, use the following form of the debug x25 EXEC command:

To display information about a specific X.25 or CMNS context, use the following form of the debug x25 EXEC command:

To display information about a specific X.25 or CMNS virtual circuit, use the following form of the debug x25 EXEC command:

To display information about traffic for all virtual circuits using a given number, use the following form of the debug x25 EXEC command. The no form of this command removes the filter for a particular virtual circuit from the debug x25 all or debug x25 events output:

To display information about traffic to or from a specific XOT host, use the following form of the debug x25 xot EXEC command:

Syntax Description

Usage Guidelines

This command is particularly useful for diagnosing problems encountered when placing calls. The debug x25 all output includes data, control messages, and flow control packets for all of the router's virtual circuits.

All debug x25 command forms can take either the events or all keyword. The keyword all is the default and causes all packets meeting the other debug criteria to be reported. The keyword events omits reports of any Data or Receive Ready (RR) flow control packets; the normal flow of Data and RR packets is commonly large as well as less interesting to the user, so event reporting can significantly decrease the processor load induced by debug reporting.

The debug x25 interface command is useful for diagnosing problems encountered with a single X.25 or CMNS host or virtual circuit.

Because no interface is specified by the debug x25 vc command, traffic on any virtual circuit that has the specified number is reported.

Virtual circuit zero (vc 0) cannot be specified. It is used for X.25 service messages, such as RESTART packets, not virtual circuit traffic. Service messages can be monitored only when no virtual circuit filter is used.

The debug x25 xot output allows you to restrict the debug output reporting to XOT traffic for one or both hosts or host/port combinations. Because each XOT virtual circuit uses a unique TCP connection, an XOT debug request that specifies both host addresses and ports will report traffic only for that virtual circuit. Also, you can restrict reporting to sessions initiated by the local or remote router by, respectively, specifying 1998 for the remote or local port. (XOT connections are received on port 1998.)

Sample Display

Figure 29 shows the debug output for an X.25 Restart event, a Call setup, data exchange, and Clear. The first two lines describe a Restart service exchange.

router# debug x25
Serial0: X.25 I R/Inactive Restart (5) 8 lci 0
  Cause 7, Diag 0 (Network operational/No additional information)
Serial0: X.25 O R3 Restart Confirm (3) 8 lci 0
Serial0: X.25 I P1 Call (15) 8 lci 1
From(6): 170091 To(6): 170090
   Facilities: (0)
   Call User Data (4): 0xCC000000 (ip)
Serial0: X.25 O P3 Call Confirm (3) 8 lci 1
Serial0: X.25 I D1 Data (103) 8 lci 1 PS 0 PR 0
Serial0: X.25 O D1 Data (103) 8 lci 1 PS 0 PR 1
Serial0: X.25 I P4 Clear (5) 8 lci 1
  Cause 9, Diag 122 (Out of order/Maintenance action)
Serial0: X.25 O P7 Clear Confirm (3) 8 lci 1

Table 38 describes the fields in this output.

The following example shows a sequence of increasingly restrictive debug x25 commands:

router# debug x25
X.25 packet debugging is on
router# debug x25 events
X.25 special event debugging is on
router# debug x25 interface serial 0
X.25 packet debugging is on
X.25 debug output restricted to interface Serial0 
router# debug x25 vc 1024
X.25 packet debugging is on
X.25 debug output restricted to VC number 1024 
router# debug x25 interface serial 0 vc 1024
X.25 packet debugging is on
X.25 debug output restricted to interface Serial0 
X.25 debug output restricted to VC number 1024 
router# debug x25 interface serial 0 vc 1024 events
X.25 special event debugging is on
X.25 debug output restricted to interface serial 0 
X.25 debug output restricted to VC number 1024