encapsulation x25 [dte | dce ] [ddn | bfe ] | [ietf ]
(Optional) Specifies operation as a DTE. This is the default X.25 mode.
(Optional) Specifies operation as a DCE.
(Optional) Specifies DDN encapsulation on an interface using DDN X.25 Standard Service.
(Optional) Specifies BFE encapsulation on an interface attached to a BFE device.
(Optional) Specifies that the interface's datagram encapsulation defaults to use of the Internet Engineering Task Force (IETF) standard method, as defined by RFC 1356.
To specify a serial interface's operation as an X.25 device, use the encapsulation x25 interface configuration command.
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 or 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 long supported the encapsulation of a number of datagram protocols, using a standard means when available and a proprietary means when necessary. Recently the IETF adopted a standard, RFC 1356, for encapsulating most types of datagram traffic over X.25. By default, X.25 interfaces use Cisco's traditional encapsulation method. To use RFC 1356 encapsulation, specify the ietf keyword. For details see the x25 map command.
To correctly interoperate with the Defense Data Network (DDN) or a Blacker Front End (BFE) device, Cisco X.25 interfaces must derive their X.121 address from the IP address assigned to that interface. To use the appropriate algorithm for deriving the X.121 address, specify either the ddn or the bfe keyword. Use the ddn keyword when connecting to the Defence Data Network (DDN), or the bfe keyword when connecting to a Blacker Front End (BFE) device. For proper operation, the derived X.121 address must not be changed.
A router DDN attachment can operate as either a DTE or a DCE device. A BFE attachment can operate only as a DTE device. The ietf option is not available if either the ddn or bfe option is selected.
The following example configures the interface for connection to a BFE device:Router(config)#interface serial 0/0Router(config-if)#encapsulation x25 bfe
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