Table Of Contents
Dial Case Study Overview
Scenario Description
Design Architecture
Service Definitions
Layer 3 IP Design
IP Subnet Rationale
Hq-access Subnet
NAS Loopback 0 Subnet
Dialer Cloud Subnet
Tahoe and Austin LAN Subnets
Call Processing Components
Overview of Tasks
Related Documents and Web Tools
Dial Case Study Overview
This case study builds a dial-up network environment using one Cisco AS5300. The access server supports remote users and remote LANs connecting with modems and ISDN routers. The remote routers in this case study are a Cisco 1604 and Cisco 766. Only IP and basic security are used.
This exercise gives you a basic foundation from which you can scale to support larger dial implementations.
The following sections are provided:
•"Scenario Description" on page 1
•"Design Architecture" on page 4
•"Overview of Tasks" on page 9
•"Related Documents and Web Tools" on page 10
Scenario Description
The case study is structured around the following three figures.
shows a headquarters network providing dial-up services to one small office/home office (SOHO), one remote office/branch office (ROBO), and remote modem users.
Figure 1-1 Business Scenario
shows some of the physical elements present at layer 1 of the Open System Interconnection (OSI) reference model. The public switched telephone network (PSTN) provides the core interconnecting fabric between devices.
Figure 1-2 OSI Layer 1 Elements
In this scenario, a single Cisco AS5300 supports 96 concurrent modem and ISDN connections using four T1 PRI lines and 96 integrated modems. Modem connections are established via the Cisco IOS lines and corresponding asynchronous interfaces. Digital ISDN connections are established via the Cisco IOS channelized serial interfaces.
shows the layer 2 and layer 3 elements. The links going across the PSTN use the Point-to-Point Protocol (PPP). In this case study scenario PPP negotiates the link control protocol (LCP), CHAP or PAP authentication, and IP Control Protocol (IPCP) to bring up IP over PPP. IPCP is the network control protocol (NCP) used in this case study. IPCP is the mechanism that opens the links and negotiates the IP parameters.
Figure 1-3 OSI Layer 2 and Layer 3
Elements
summarizes the types of services provided by the headquarters POP to the remote nodes and sites. For more information, see .
Table 1-1 Scenarios and Site Characteristics Provided by Headquarters
Scenario
|
|
Services Required
|
Notes
|
Remote node modem
|
Modem
|
Asynchronous shell2 (async shell) Asynchronous PPP (async PPP)
|
Dial in only4. Remote devices are assigned an IP address from a central pool.
|
Remote node ISDN
|
ISDN routers using port address translation (PAT)3 , PC-based ISDN terminal adapters
|
Synchronous PPP (sync PPP)
|
Dial in only4 . PAT enabled. Connecting devices are assigned an IP address from a central pool.
|
Remote office LAN
|
Cisco 1604
|
Synchronous PPP
|
Dial in and dial out4. Distinct IP subnet. PAT not used.
|
Small office LAN
|
Cisco 766
|
Synchronous PPP
|
Dial in and dial out4. Distinct IP subnet. PAT not used.
|
Design Architecture
The following sections provide the framework for this case study:
•Service Definitions
•Layer 3 IP Design
•IP Subnet Rationale
•Call Processing Components
Service Definitions
In this case study, the Cisco AS5300 offers three basic services: async shell, async PPP, and sync PPP. See .
These services are based on real needs as requested by the remote sites. To access these services, remote devices connect to the Cisco AS5300 via the PSTN.
Table 1-2 Services Provided by Headquarters
Service Term
|
Purpose
|
|
Security Method Used
|
Async shell
|
Provides access to Cisco IOS terminal services (no PPP) to do the following:2
•Change passwords
•Access menus
•Troubleshoot modem connections using a simple environment
•Access other network resources via telnet
|
Client modems, POTS3 , Cisco IOS integrated modems, lines, and asynchronous interfaces
|
Login
|
Async PPP
|
•Provides IP (and multi-protocol) connectivity for remote node modem users
•Supports any Internet application available using IP such as e-mail, web browsing, FTP, and Telnet.
|
Client modems, POTS3, Cisco IOS integrated modems, lines, and asynchronous interfaces
|
PPP (CHAP, PAP, or login)
|
Sync PPP
|
•Provides IP (and multi-protocol) connectivity for BRI or PRI attached remote sites.
•Supports any Internet application available using IP such as e-mail, web browsing, FTP, and Telnet4 .
|
End-to-end ISDN using B channels over a digital synchronous path, calls use interface serial channels (for example, S0:1, S0:2, and so forth)
|
PPP (CHAP or PAP)
|
Layer 3 IP Design
This case study uses PPP to transport IP packets across the PSTN and into the end-user devices (remote LAN or remote node). IPCP is the specific service enabled over the PPP links. To deliver this service, the case study uses address space from 10.1.0.0 /16. See the following figures and tables for the IP subnetting plan.
Figure 1-4
IP Subnetting Diagram
Table 1-3 IP Subnetting Plan
Subnet Name
|
Assigned Subnet
|
Location
|
Hq-access
|
10.1.1.0 /24
|
Hq-access Ethernet
|
NAS loopback 01
|
10.1.2.0 /24
|
Loopback interface inside the Cisco AS5300
|
Dialer cloud
|
10.1.254.0 /24
|
Public switched telephone network
|
Tahoe LAN
|
10.1.3.0 /24
|
Tahoe Ethernet
|
Austin LAN
|
10.1.4.0 /24
|
Austin Ethernet
|
...2
|
...
|
...
|
...
|
...
|
...
|
Using the subnetting plan and topologies shown in the previous tables and figures, a router naming and addressing plan is created in . Notice that the IP addresses are derived directly from the subnet plan.
Table 1-4 Router IP Addressing Plan
|
WAN IP Address
|
Ethernet IP Address
|
hq-sanjose
|
10.1.254.1 255.255.255.0
|
10.1.1.10 255.255.255.0
|
soho-tahoe
|
10.1.254.3 255.255.255.0
|
10.1.3.1 255.255.255.0
|
robo-austin
|
10.1.254.4 255.255.255.0
|
10.1.4.1 255.255.255.0
|
...2
|
...
|
...
|
...
|
...
|
...
|
IP Subnet Rationale
This section describes each IP subnet and its design criteria. IP route summarization occurs at the gateway that connects the NAS to the IP backbone. IP range 10.1.0.0/16 is propagated to the backbone.
Hq-access Subnet
IP subnet 10.1.1.0/24 is assigned to the Ethernet connected to the Cisco AS5300. If additional access servers and POP management devices are needed, they are assigned to this IP subnet. Using one subnet for the entire headquarters dial access POP simplifies network design.
NAS Loopback 0 Subnet
IP subnet 10.1.2.0/24 is assigned to the loopback interface on the Cisco AS5300. This is the subnet used to host the remote node IP addresses. The access server has an IP pool range of 10.1.2.2 through 10.1.2.97.
Remote nodes dialing in request addresses from the Cisco AS5300's local IP address pool. This IP pool behaves like an address server handing out IP addresses to remote nodes during IPCP negotiation (a component of PPP).
Dialer Cloud Subnet
IP subnet 10.1.254.0/24 is assigned to the PSTN/ISDN. The static IP addresses are described in . See the column "WAN IP Address." The PSTN/ISDN becomes a "dialer cloud" from the Cisco IOS perspective. Dialer interfaces are used to connect to this dialer cloud. BRI and PRI interfaces are also dialer interfaces and use the same dial-on-demand routing (DDR) mechanisms to open and close circuit-switched connections.
A key design decision in this case study is to number the dialer cloud subnet. (That is, IP unnumbered is not used on these interfaces.) Numbering the dialer cloud ports to match the remote LAN supported by the same remote device is part of our design strategy to simplify administration. For example, remote subnet 10.1.3.0/24 is connected to the same remote site as dialer cloud node 10.1.254.3. IP node 10.1.254.4 supports IP subnet 10.1.4.0/24.
On the Cisco AS5300, all the individual serial channel interfaces are grouped together under one master dialer interface. As the individual remote sites connect, their configurations must coordinate with the configuration of the master dialer interface.
Tahoe and Austin LAN Subnets
IP subnet 10.1.3.0/24 is assigned to the Ethernet connected to the Cisco 766 (soho-tahoe). IP subnet 10.1.4.0/24 is assigned to the Cisco 1604 (robo-austin) Ethernet. Each site that supports a distinct IP subnet must be assigned its own distinct IP subnet address space. Routers with LANs behind them must have their own distinct IP subnets when not using PAT.
These remote LAN routers point to the central site as the default route. The hq-sanjose NAS is configured with static routes to the remote IP subnets.
Call Processing Components
illustrates the connectivity path as calls come into the Cisco AS5300. The contents inside the dotted square box are the internal components of the Cisco AS5300. Both analog modem and digital calls enter the Cisco AS5300 via the E1/T1 controllers. Incoming modem calls are connected with the integrated modems and routed to the asynchronous interfaces. Incoming sync PPP calls are connected to the individual serial channels (for example, S0:1 and S0:2).
As shown in , one PPP/modem user consumes resources from one channel, one integrated modem, one line, and one asynchronous interface. An ISDN B-channel user connects directly via a channel of the T1 and a serial B-channel. The group-async and dialer interfaces are used to control the interfaces' behavior and configuration of async and serial channels.
Figure 1-5 Call Processing Components
Overview of Tasks
The network devices in this case study are manually configured using Cisco IOS software. The automatic Cisco IOS setup script is not used. This setup script usually runs when no startup configuration is found in NVRAM (for example, when powering up a new router).
Here is the action plan to build the network. For step-by-step configuration tasks, refer to the device-specific configuration chapters that follow.
Step 1 Set up async shell services on the Cisco AS5300. See chapter 2 "."
–Configuring the Host Name, Password, and Time Stamps
–Configuring Local AAA Security
–Configuring the Fast Ethernet 100BaseT Interface
–Commissioning the T1 Controllers
–Configuring the Serial Channels to Let Modem Calls Come in
–Configuring the Modems and Lines
–Testing Async Shell Connections
Step 2 Set up async PPP services on the Cisco AS5300. See chapter 2 "."
–Setting Up IP Address Pools
–Configuring the Group-Async Interface
–Testing Async PPP Connections
Step 3 Set up synchronous PPP services on the Cisco AS5300. See chapter 2 "."
–Configuring DDR
–Configuring Definitions for Remote LAN Sites
–Configuring a Backhaul Routing Protocol
–Confirming the Final Running Configuration
–Saving the Configuration
–Testing Sync PPP Connections to Remote LANs
–Adding More Remote LAN Sites as Needed
Step 4 Configure the Cisco 1604 to dial into the Cisco AS5300. See chapter 3 "."
–Configuring the Host Name, Password, and Time Stamps
–Configuring Local AAA Security
–Configuring the Ethernet Interface
–Configuring BRI
–Configuring DDR
–Testing Connections to the Cisco AS5300
–Confirming the Final Running Configuration
–Saving the Configuration
Step 5 Configure the Cisco 766 to dial into the Cisco AS5300. See chapter 4 "."
–Configuring System Level Settings
–Configuring the LAN Profile
–Configuring the Site Profile hq-sanjose
–Testing Connections to the Cisco AS5300
–Confirming the Final Running Configuration
Related Documents and Web Tools
Refer to the following online resources for more information:
•Internetworking Case Studies—Provides practical examples of how to implement Cisco IOS software features. Case studies address implementation concerns and show how to apply features to their best advantage. Detailed configuration file examples and network diagrams are included.
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ics/index.htm
•Cisco Access Dial Configuration Cookbook—Contains common configurations or recipes to configure various access routers and dial technologies. It covers common configurations for async, dial-on-demand routing (DDR), integrated services digital network (ISDN), and other access dial concepts including basic security. It also provides configurations for the Cisco 700, AS5200, and AS5300. You must be a registered Cisco Connection Online (CCO) user to gain access to this publication.
http://www.cisco.com/warp/public/793/access_dial/
•Dial Solutions Configuration Guide and Command Reference—Provides a comprehensive library of Cisco's dial software features, which are configured using the command line interface.
http://www.cisco.com/univercd/cc/td/doc/product/software/ios113ed/113ed_cr/index.htm
•Internetworking Technology Overview, Point-to-Point Protocol—Describes the background and general operation of PPP.
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/55168.htm
•Troubleshooting Engine—Helps you solve common problems involving hardware, configuration, and performance.
http://te.cisco.com/cgi-bin/webcgi.exe?New,KB=TE
•Cisco AS5x00 Access Server Documentation—Includes software and hardware configuration guides for Cisco's access server product line.
http://www.cisco.com/univercd/cc/td/doc/product/access/acs_serv/index.htm
Note These URLs can change without notice.