Choosing your authentication method
5.1.2.3 IP address negotiation using DHCP
The Dynamic Host Configuration Protocol DHCP is an ideal way to configure incoming PPTP clients with a dynamic IP address. Windows NT 4.0 comes with a DHCP server service that must be installed through the Network Control Panel. [1] Follow the instructions for installing RAS, but install the Microsoft DHCP Server service instead. Once the service is installed, a DHCP Manager program will also be installed under the Start menu in Administrative Tools. To configure DHCP, follow these steps: 1. Under the Start Programs Administrative Tools listing, open the DHCP Manager. The DHCP Manager dialog box will appear see Figure 5-3 . 2. Under the DHCP Servers column, select the Local Machine. Then go to the Scope menu item and select Create. 3. The Create Scope dialog box shown in Figure 5-3 will appear. Enter the Start Address and End Address for your assignments. In our case, well choose 2.1.1.129 for the starting address and 2.1.1.136 for the ending address. Figure 5-3. The Windows NT DHCP Manager 1 DHCP will not work on a Windows NT 4.0 RAS server that has two network cards with PPTP filtering enabled on one of them. Microsoft found the problem and issued a fix in Windows NT 4.0 Service Pack 2. We recommend having Service Pack 3 or later installed if you want to use DHCP with RAS. See other problems between DHCP and PPTP filtering in Section 5.1.3.2 later in this chapter. 74 4. Enter the Subnet Mask for the range. Since these addresses are part of the 2.1.1.0 range, well enter 255.255.255.0. 5. At this point, well leave the Exclusion Range addresses blank. We dont want to exclude any addresses from this range. 6. Well enter the Name of the scope as Dial-Up Address Range, then click OK. When a dialog asks you if you want to activate the scope, click Yes. If you have several RAS servers, youll probably want to use the DHCP Relay Agent NT service, also installed through the Network Control Panel. Using this service, the RAS server will forward a connecting clients request for an IP address to a DHCP server specified in the DHCP Relay Agent properties. This allows you to assign IP addresses from a single, central pool for every RAS server on your network, even across different LANs.5.1.3 PPTP Filtering
We discussed what PPTP filtering does at the beginning of this chapter. To set up PPTP filtering, open the Network Control Panel, click on the Protocols tab and choose TCP IP, then click the Properties button. Finally, click the Advanced button on the TCP IP setup dialog box. At the bottom of the Advanced IP Addressing box is the Enable PPTP Filtering checkbox.5.1.3.1 Outbound authentication using PPTP filtering
On multihomed hosts, PPTP filtering can also be used as a type of outbound firewall by enabling it on the network adapter connected to the LAN. Users on the internal network would dial the PPTP server as if they were coming over a PPP link, using the RAS servers IP address as the phone number. They would then be forced to authenticate at the RAS server in order to tunnel out to the Internet using the servers routing capabilities. This allows a network administrator to limit Internet access, monitor whos accessing the Internet and for how long, and limit the number of simultaneous Internet connections.5.1.3.2 Filtering caveats
Enabling PPTP filtering on a Windows NT 4.0 system with only one network card can make other NT network services you might be running such as the DHCP server service and the FTP server service inaccessible to non-PPTP clients; the adapter will require PPTP authentication on any request it gets. There is a way to allow packets to reach the RAS server itself, without going to the network beyond. To do so you must install the Windows NT 4.0 Service Pack 3 or later version and add a particular entry to the Windows NT Registry. Editing the Windows NT Registry can be very dangerous. Invalid data entry could corrupt the Registry and cause numerous—possibly irreversible—system problems. You may be forced to reinstall Windows NT. As always, make sure you have a recent backup of your system. Run the Registry Editor by selecting the Run option under the Start menu and entering REGEDIT.EXE in the filename field. The parameter to add is under the following Registry key:Parts
» Virtual Private Networks 2nd 1999
» How VPNs relate to Intranets
» What Are We Protecting with Our VPN?
» Firewalls How VPNs Solve Internet Security Issues
» Authentication How VPNs Solve Internet Security Issues
» Encryption How VPNs Solve Internet Security Issues
» Tunneling How VPNs Solve Internet Security Issues
» A Note on IP Address and Domain Name Conventions Used in This Book
» Packet restriction or packet filtering routers
» Bastion host What Types of Firewalls Are There?
» DMZ or perimeter zone network
» Proxy servers What Types of Firewalls Are There?
» A Brief History of Cryptography
» Cryptography: How to Keep a Secret
» Cryptography in Network Communications
» Hash algorithms Cryptographic Algorithms
» Secret key systems Cryptographic Algorithms
» Public key cryptosystems Cryptographic Algorithms
» Use of Cryptosystems and Authentication in a VPN
» ESP Encapsulating Security Payload
» AH Authentication Header VPN Protocols
» Internet Key Exchange, ISAMKPOakley
» ISO X.509 v.3 Digital Certificates
» LDAP Lightweight Directory Access Protocol Radius
» PPTP Point-to-Point Tunneling Protocol
» Basic Firewalling Methodologies for Compromising VPNs
» Ciphertext-only attack Cryptographic Assaults
» Known plaintext attack Cryptographic Assaults
» Chosen plaintext attack Cryptographic Assaults
» Chosen ciphertext attack Cryptographic Assaults
» Brute force attacks Cryptographic Assaults
» Password guessers and dictionary attacks
» Social engineering Cryptographic Assaults
» Address spoofing Network Compromises and Attacks
» Session hijacking Network Compromises and Attacks
» Man-in-the-middle attack Network Compromises and Attacks
» Replay attack Network Compromises and Attacks
» Detection and cleanup Network Compromises and Attacks
» Patents and Legal Ramifications
» General WAN, RAS, and VPN Concepts
» Telco Small to Medium Solutions
» Security, scalability, and stability
» Hardwaresoftware Small to Medium Solutions
» Administration Small to Medium Solutions
» Hardwaresoftware Administration Security, scalability, and stability
» Differences Between PPTP, L2F, and L2TP
» Dialing into an ISP That Supports PPTP
» Dialing into an ISP That Doesnt Support PPTP
» Where PPTP Fits into Our Scenario
» The encapsulation process Dissecting a PPTP Packet
» Accept encrypted authentication RAS authentication methods
» Accept Microsoft encrypted authentication
» Accept any authentication, including clear text
» Data encryption PPTP Security
» Availability Features of PPTP
» Easy Implementation Features of PPTP
» Multiprotocol Tunneling Features of PPTP
» Ability to Use Corporate and UnregisteredIP Addresses
» Choosing the protocols to tunnel
» Choosing your authentication method
» IP address negotiation using DHCP
» Outbound authentication using PPTP filtering
» Filtering caveats PPTP Filtering
» Installing PPTP Filtering by IP Address
» Configuring Users for Dial-up Access
» Configuring PPTP for Dial-up Networking on a Windows NT Client
» Configuring PPTP for Dial-up Networking on a Windows 95 or 98 Client
» Setting up global PPTP parameters Setting up a port for PPTP
» Configuring PPTP on an Ascend MAX 4004
» Making the Calls Configuring and Testing Layer 2 Connections
» The Event Viewer Login problems
» The Dial-Up Networking Monitor
» ping and traceroute Connectivity Testing
» Fixed IP addresses How to Allow PPTP Through Firewalls
» How PPTP Can Bypass a Proxy Server
» Three-part encryption technique Security
» Support for an emerging security standard
» Support for Security Dynamics SecureID
» Accessibility Flexibility Advantages of the AltaVista Tunnel System
» Platform Limitations AltaVista Tunnel Limitations
» Extranet server System Considerations
» Telecommuter client System Considerations
» Planning How the AltaVista Tunnel Works
» AltaVista Tunnel Extranet server
» Security procedures The Guts
» AltaVista Tunnel Telecommuter Client
» Sample configuration Implementing a LAN-to-LAN Tunnel
» Tunnel server configuration Implementing a LAN-to-LAN Tunnel
» Firewall configuration Host configuration
» Sample configuration Implementing Single Connections-to-LAN Tunnels
» Tunnel server configuration Implementing Single Connections-to-LAN Tunnels
» Firewall configuration Implementing Single Connections-to-LAN Tunnels
» Local host configuration Implementing Single Connections-to-LAN Tunnels
» Remote PC configuration Implementing Single Connections-to-LAN Tunnels
» Sample configuration Implementing PC-to-WAN Tunnels
» Tunnel server configuration Implementing PC-to-WAN Tunnels
» Tracing the packets Implementing PC-to-WAN Tunnels
» Preparing to Install Installing the AltaVista Tunnel
» Windows NT 4.0 Installing the AltaVista Tunnel Extranet Serverfor Windows NT
» Installing the AltaVista Tunnel Telecommuter Client for Windows
» Installing the AltaVista Tunnel Telecommuter Client for MacOS
» Initial configuration Adding Routes and Dynamic Addresses
» Managing routes and dynamic IPs
» Group configuration Adding Tunnel Groups
» Tunnel client information Adding Tunnel Groups
» Tools for Tunnel Management Changing Port Settings
» Rekey Interval and Minimum Encryption Settings
» Configuring Unix-to-Windows NT Tunnel Connections
» Getting Busy Configuring the AltaVista Telecommuter Client
» Tunnel Server and Client Configuration Checks
» Local Network and Internet Gateway Configuration Checks
» Encryption Capabilities The SSH Software
» Useful sshd parameters for our purposes
» Understanding SSH authentication ssh
» Useful ssh parameters for our purposes
» The VPN Components Creating a VPN with PPP and SSH
» Setting up the master and slave Linux systems
» Creating a user account on the slave
» Setting up SSH authentication
» Configuring sudo on the slave
» Putting pty-redir on the master
» Setting up the slaves scripts
» Testing the Connection Creating a VPN with PPP and SSH
» A Performance Evaluation Creating a VPN with the Unix Secure Shell
» ISP Assigned Addresses Global Pool
» Hardware solution Advantages of the PIX Firewall
» Superior to Unix and other router firewalls
» Single point of controlfailure
» Dynamic address translation Advantages of the PIX Firewall
» PIX acts like a proxy server
» Ease of configuration and maintenance
» High-speed access Advantages of the PIX Firewall
» Links Advantages of the PIX Firewall
» Hardware solution Limitations of the PIX Firewall
» Dynamic address use Limitations of the PIX Firewall
» Budgetary considerations Limitations of the PIX Firewall
» Maintenance Limitations of the PIX Firewall
» A Sample Configuration Configuring the PIX as a Gateway
» Firewall Configuration on the PIX
» debug xlate Testing, Tracing, and Debugging
» arp Testing, Tracing, and Debugging
» show interface Testing, Tracing, and Debugging
» Offering Services to the Internet Through Conduits and the static Command
» Tunneling with the link Directive
» Choosing an ISP Managing and Maintaining Your VPN
» Connectivity Problems Solving VPN Problems
» Authentication Errors Solving VPN Problems
» Routing Problems Dealing with an ISP
» Compatibility with Other Products
» Delivering Quality of Service
» Restrict What VPN Users Can Get To
» Avoid Public DNS Information for VPN Servers and Routers
» Keeping Yourself Up-to-Date Managing and Maintaining Your VPN
» Network Connections Hardware and Operating System VPN Package
» Connection Hardware and Operating System VPN Package
» Connection Hardware and Operating System
» VPN Package Remote Access Users
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