Accept any authentication, including clear text
4.2.5.2 Data encryption
In the RAS properties for Windows NT, youll find a checkbox to require data encryption for the RAS connection. This option will make all data going across the connection stream unreadable to an interceptor. The box can be checked only if the option to require Microsoft encrypted authentication is also selected, meaning that you can use it only if youre also using MS-CHAP. The reason for this is that the value generated by the MD4 hash is used by the RAS client and server to derive a session key for encryption. The encryption algorithm used is RSAs RC4, with a 40-bit session key. As we said in Chapter 2 , U.S. export laws prevent the distribution of ciphers that can use session keys of greater than 40 bits. On the other hand, keys of 40 bits are often considered too vulnerable for transmitting secure data over the Internet. In order to meet the demand for better encryption methods, Microsoft has included a 128-bit strong encryption module in a U.S.-only version of their Service Pack 3 for Windows NT 4.0.4.3 Features of PPTP
There are several factors in PPTPs favor. Among these are availability, easy implementation, multiprotocol tunneling, and the ability to use corporate and unregistered IP addresses.4.3.1 Availability
Because PPTP is included with Windows NT Server, Workstation, and Windows 98, it is readily available to users of these platforms. No additional software need be purchased. Microsoft is giving away the PPTP upgrade for Windows 9598 as well. In addition, it is included free of charge in many different brands of remote access switches, including Ascend, 3Com, and ECI Telematics equipment. Because it has become part of the package of a leading network operating system and numerous remote access switches, PPTP enjoys a huge product-placement advantage. An administrator for a Windows NT network can start experimenting with a VPN right away, without spending any extra money.4.3.2 Easy Implementation
On Windows NT systems, PPTP is installed as a network protocol, just like IPX SPX, TCPIP, or NetBEUI. In RAS, instead of using a modem as the RAS device, you use a VPN port with the name RASPPTPM. Many Windows NT administrators will already be familiar with how to set up network protocols and RAS, so using PPTP shouldnt be difficult for them. Likewise, on Windows 95 systems, PPTP is installed as a new version of the Dial-Up Adapter thats already a familiar part of Windows 95 Dial-Up Networking. On Windows 98, the VPN Adapter can also be installed and used like a modem for VPN connections. On remote access switches that support PPTP, enabling PPTP is typically straightforward. For users who wish to dial in using PPTP, you simply add the IP address of their PPTP server to their profiles. ISPs that use authentication and accounting software such as Merit Networks RADIUS server will also find PPTP as easy to implement in a user profile as PPP. Well go into detail about how to set up PPTP on both RAS and remote access switches in Chapter 5 . 684.3.3 Multiprotocol Tunneling
The ability to tunnel multiple protocols is one of PPTPs greatest advantages. Some tunneling software allows you to tunnel only IP packets. PPTP, however, can tunnel all of the protocols currently supported by RAS. Users connecting to a RAS server through a VPN will have access to the full range of protocols and servers they would normally have on their LAN. For Windows NT and Windows 9598 users, this means that their usual username and password, and all access privileges associated with their profile, will pertain to the dial-up user. They will be able to browse the network and access file servers and network printers, as always, through their Network Neighborhood.4.3.4 Ability to Use Corporate and UnregisteredIP Addresses
When VPN users make PPTP connections with the RAS server, they can be assigned IP addresses by that server. The address can be part of the corporations range of IP addresses 2.1.1.129 is part of the 2.1.1.024 CIDR address range in our earlier examples, thus making the RAS users system appear to be on the corporate IP network. Sometimes corporations dont use what are known as registered IP addresses on their internal networks. If a block of addresses is registered, it means that it was obtained by an address registry such as the InterNIC that assures that the addresses are unique on the Internet. The Internet Assigned Numbers Authority IANA has set aside blocks of unregistered IP addresses for use on private internets, or Intranets. These addresses can be used on IP networks that dont have Internet access or that have access through a router that uses Network Address Translation or NAT, which well discuss more later. A listing of these unregistered blocks of addresses can be found in RFC 1918. If a company is using an unregistered range of addresses, a RAS client using PPTP can obtain one of these addresses and have access to the corporate IP network. If the user were simply dialing into an ISP and attempting to access the network without PPTP, a hole in the corporate firewall would have to be opened up for that user. If the user obtains a dynamic IP address whenever they dial into their ISP, this would be nearly impossible.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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