X.25 Station Type for ISDN D-channel Interface

If the D channel of an ISDN BRI interface will carry X.25 traffic, you need to configure the feature that is described in the Configuring X.25 on ISDN feature guide.

A BRI is an ISDN interface. It consists of two B channels (B1 and B2) and one D-channel. The B channels are used to transfer data, voice, and video. The D channel controls the B channels.

ISDN uses the D-channel to carry signal information. ISDN can also use the D-channel in a BRI to carry X.25 packets. The D-channel has a capacity of 16 kbps; the X.25 over D-channel can use up to 9.6 kbps.

When this feature is configured, a separate X.25-over-D-channel logical interface is created. You can set its parameters without disrupting the original ISDN interface configuration. The original BRI interface will continue to represent the D, B1, and B2 channels.

An interface configured for X.25 traffic over the D channel can be used as a primary interface where low-volume, sporadic, interactive traffic is the normal mode of operation. Supported traffic includes IPX, AppleTalk, transparent bridging, XNS, DECnet, and IP.

For more details on how to configure the X.25 over ISDN D-channel Interface feature, see the following URL:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios113ed/113ed_cr/dial_c/dcprt10/dcxisdn.htm

A closed user group (CUG) is a collection of DTE devices for which the network controls access between two members and between a member and a non-member. An X.25 network can support up to 10,000 CUGs (numbered between 0 and 9999), each of which can have any number of member DTE devices. An individual DTE becomes a member of a specific network CUG by subscription. The subscription data includes the local number that the DTE will use to identify the network CUG (which may or may not be the same as the network number, as determined by network administration and the DTE device's requirements), and any restriction that prohibits the DTE from placing a call within the CUG or, conversely, prohibits the network from presenting a call within the CUG to the DTE.

With the X.25 CUGs feature, the router's X.25 DCE interfaces can be configured to perform the standard CUG access controls that are normally associated with a direct attachment to an X.25 network point of presence (POP). The router's DCE interface acts as the boundary between the DTE and the network, and CUG use ensures that only those incoming and outgoing switched virtual circuits (SVCs) consistent with the configured CUG subscriptions are permitted. X.25 CUG configuration commands on the router are specified at every POP, and CUG security decisions are made solely from those commands.

The X.25 CUGs feature is used for additional X.25 access protection and security. In a setup where DTE devices are attached to a public data network (PDN), you can derive a private subnetwork by subscribing your DTE devices to a set of CUGs, which allows closer control of your DTE devices, such as permitting or restricting which DTE can talk to other DTE devices and for what particular purpose. For example, a distinct CUG can be defined to handle each of the different modes of connectivity, such as following:

• Datagram encapsulation operation between all company sites
• Packet assembler/disassembler (PAD) services for customers seeking public information
• PAD services for system administration internal access to consoles
• Qualified Logical Link Control (QLLC) access restricted to the company financial centers

For more details, see the following URL:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newft/120t/120t7/x25scugs.htm

Note	Use the interface BRI2/0 and isdn x25 dchannelcommands if the configurable interface for X.25 traffic over ISDN D-channel does not exist.

To configure X.25 encapsulation on ISDN BRI D-channel Interface, perform the following steps.

1.    enable

2.    configure terminal

3.    interface BRI2/0

4.    isdn x25 dchannel

5.    interface BRI2/0:0

6.    encapsulation X25 dce

7.    end

interface BRI2/0:0
ip address 1.1.1.2 255.255.255.0
 encapsulation X.25 dce
 no ip mroute-cache
 X.25 subscribe cug-service
 X.25 subscribe local-cug 10 network-cug 100
!

The following example shows X.25 encapsulation configured on interface BRI2/0:

Current configuration: 2275 bytes
!
version 12.3
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname Router
!
boot system flash c1700-voice-mz
enable password cisco
!
memory-size iomem 15
tdm clock bri-auto
voice-card 2
!
no aaa new-model
ip subnet-zero
!
!
!
no ftp-server write-enable
isdn switch-type basic-net3
!
no voice hpi capture buffer
no voice hpi capture destination
!
interface FastEthernet0/0
 ip address 10.0.2.199 255.255.255.0
 speed 100
!
interface BRI2/0
no ip address
 isdn switch-type basic-net3
 isdn protocol-emulate network
 isdn layer1-emulate network
 no isdn outgoing display-ie
 isdn x25 static-tei 1
 isdn x25 dchannel
 isdn skipsend-idverify
!
interface BRI2/0:0
no ip address
encapsulation x25 dce
x25 subscribe cug-service incoming-access outgoing-access
x25 subscribe local-cug 5000 network-cug 55 preferential
!
interface BRI2/1
 no ip address
 shutdown
 isdn switch-type basic-net3
!
ip classless
no ip http server
!
voice-port 2/0
!
voice-port 2/1
!
line con 0
line aux 0
line vty 0 4
login
!
end