Cisco IOS Wide-Area Networking Configuration Guide - Free Books

Configuring X.25 Closed User GroupsConfiguring X.25 and LAPBConfiguring a POP with Multiple CUGs and Public AccessThe least restrictive POP configuration is a POP configured to allow public access to members of severalCUG and to originate and receive calls from the open network (that is, to or from users that do notsubscribe to one of the CUGs to which this POP subscribes). Configuring the POP with multiple CUGsand public access is achieved using the x25 subscribe cug-service command with the addition of thekeywords incoming-access and outgoing-access to allow calls to be made and received to and fromoutside hosts not in the specified CUG network.To set up the individual CUGs, use the x25 subscribe local-cug command to specify each local CUGand map it to a network CUG, setting the access properties of the local CUG—no-incoming,no-outgoing, preferential, all, or none—at the same time.An outgoing call may select any of the local CUGs or not. When no CUG is selected, it is assumed thatthe call is intended for the open network. The call will be refused if it specifies a local CUG differentfrom the one to which the POP is subscribed. An incoming call may or may not select related networkCUGs. If no CUG is selected, the call is accepted as coming from the open network. A call that requiresaccess to a different CUG will be refused.To configure a POP with multiple CUGs and public access, use the following commands beginning inglobal configuration mode:CommandPurposeStep 1 Router(config)# interface number Selects the interface to be configured.Step 2 Router(config-if)# encapsulation x25 dce Enables X.25 DCE network operation.Step 3Step 4Step 5Router(config-if)# x25 subscribe cug-serviceincoming-access outgoing-accessRouter(config-if)# x25 subscribe local-cug numbernetwork-cug number [no-incoming | no-outgoing |preferential]Router(config-if)# x25 subscribe local-cug numbernetwork-cug number [no-incoming | no-outgoing |preferential]Permits incoming and outgoing CUG accesson an X.25 DCE interface.Maps the desired local CUG number to itscorresponding network CUG.Configures another CUG interface.For an example of configuring a POP with multiple CUGs and public access, see the section “POP withMultiple CUGs and Public Access Example” at the end of this chapter.Configuring CUG Selection Facility SuppressionA CUG selection facility is a specific encoding element that can be presented in a call request or anincoming call. A CUG selection facility in a call request allows the source DTE to identify the CUGwithin which it is placing the call. A CUG selection facility in an incoming call allows the destinationDTE to identify the CUG to which both DTEs belong.You can configure an X.25 DCE interface or X.25 profile with a DCE station type to selectively removethe CUG selection facility before presenting an incoming call packet to a subscribed DTE. The CUGselection facility can be removed from incoming call packets destined for the preferential CUG only orfor all CUGs. You can also remove the selection facility from a CUG with outgoing access (CUG/OA).The CUG selection facility suppression mechanism does not distinguish between CUGs and CUG/OAs.NoteThe CUG Selection Facility Suppress Option feature will not in any way compromise CUG security.52