Cisco IOS Wide-Area Networking Configuration Guide - Free Books

Configuring X.25 and LAPBConfiguring X.25 Closed User GroupsStep 1Perform the standard priority and custom queueing tasks except the task of assigning a priority or customgroup to the interface, as described in the chapters “Configuring Priority Queueing” and “ConfiguringCustom Queueing” in the Cisco IOS Quality of Service Solutions Configuration Guide.Step 2 Perform the standard X.25 encapsulation tasks, as specified in the section “Configuring an X.25Datagram Transport” earlier in this chapter.Step 3Assign either a priority group or a custom queue to the interface, as described in the chapters“Configuring Priority Queueing” and “Configuring Custom Queueing” in the Cisco IOS Quality ofService Solutions Configuration Guide.NoteConnection-oriented VCs (for example, QLLC, PAD, and switched X.25) will use the default queue ofthe interface. To maintain the correct order, all connection-oriented VCs use a single output queue forsending data.Configuring X.25 Closed User GroupsA closed user group (CUG) is a collection of DTE devices for which the network controls access betweentwo members and between a member and a nonmember. An X.25 network can support up to 10,000CUGs (numbered from 0 to 9999), each of which can have any number of member DTE devices. Anindividual DTE becomes a member of a specific network CUG by subscription. The subscription dataincludes the local number the DTE will use to identify the network CUG (which may or may not be thesame as the network number, as determined by network administration and the requirements of the DTEdevice), 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 device.The X.25 DCE interfaces of the router can be configured to perform the standard CUG access controlsnormally associated with a direct attachment to an X.25 network POP. The DCE interface of the routeracts as the boundary between the DTE and the network, and CUG use ensures that only those incomingand outgoing SVCs consistent with the configured CUG subscriptions are permitted. X.25 CUGconfiguration commands on the router are specified at every POP, and CUG security decisions are madesolely from those commands. However, CUG service is not supported on XOT connections.CUG security depends on CUG decisions made by the two POPs used to connect an SVC through thenetwork, so CUG security depends on the collective configuration of all POPs that define the networkboundary. The standalone interface configuration determines if the POP will permit user access for agiven incoming or outgoing call within the authorized CUG.CUGs are a network service designed to allow various network subscribers (DTE devices) to besegregated into private subnetworks with limited incoming or outgoing access. This means that a DTEmust obtain membership from its network service (POP) for the set of CUGs it needs access to. A DTEmay subscribe to zero, one, or several CUGs at the same time. A DTE that does not require CUGmembership for access is considered to be in the open part of the network. Each CUG typically permitssubscribing users to connect to each other, but precludes connections with nonsubscribing DTE devices.However, CUG behavior is highly configurable. For instance, a CUG configuration may subscribe a DTEto a given CUG, but bar it from originating calls within the CUG or, conversely, bar it from receivingcalls identified as being within the CUG. CUG configuration can also selectively permit the DTE tooriginate calls to a DTE on the open network, or permit the DTE to receive calls from a DTE on the opennetwork.45