Cisco IOS Wide-Area Networking Configuration Guide - Free Books

Configuring X.25 and LAPBConfiguring Additional X.25 Interface ParametersThe null X.121 address (the X.121 address that has zero digits) is a special case. The router acts as thedestination host for any call it receives that has the null destination address.A subaddress is an X.121 address that matches the digits defined for the X.121 address of the interface,but has one or more additional digits after the base address. X.25 acts as the destination host for anincoming PAD call with a destination that is a subaddress of the address of the interface; the trailingdigits specify which line a PAD connection is requesting. This feature is described in the chapter“Configuring Protocol Translation and Virtual Asynchronous Devices” in the Cisco IOS TerminalServices Configuration Guide. Other calls that use a subaddress can be accepted if the trailing digit ordigits are zeros; otherwise, the router will not act as the destination host of the call.To configure X.25 addresses, perform the tasks in the following sections:• Configuring an Interface Alias Address• Suppressing or Replacing the Calling Address• Suppressing the Called AddressConfiguring an Interface Alias AddressYou can supply alias X.121 addresses for an interface. Supplying alias addresses allows the interface toact as the destination host for calls having a destination address that is neither the address of theinterface, an allowed subaddress of the interface, nor the null address.Local processing (for example, IP encapsulation) can be performed only for incoming calls whosedestination X.121 address matches the serial interface or alias of the interface.To configure an alias, use the following command in interface configuration mode:CommandRouter(config-if)# x25 aliasx121-address-pattern [cud pattern]PurposeEnables an alias X.121 address for the interface.Suppressing or Replacing the Calling AddressSome attachments require that no calling (source) address be presented in outgoing calls. Thisrequirement is called suppressing the calling address. When attached to a PDN, X.25 may need to ensurethat outgoing calls use only the assigned X.121 address for the calling (source) address. Routed X.25normally uses the original source address. Although individual X.25 route configurations can modify thesource address, Cisco provides a simple command to force the use of the interface address in all callssent; this requirement is called replacing the calling address.To suppress or replace the calling address, use the appropriate command in interface configuration mode:CommandRouter(config-if)# x25 suppress-calling-addressRouter(config-if)# x25 use-source-addressPurposeSuppresses the calling (source) X.121 address in outgoing calls.Replaces the calling (source) X.121 address in switched calls.Suppressing the Called AddressSome attachments require that no called (destination) address be presented in outgoing calls; thisrequirement is called suppressing the called address.17