Nat Considerations

PPTP VPN client can be placed behind a Network Address Translation (NAT), the NAT server is a PPTP NAT editor. (The NAT editor is a software that includes the addition of a specific protocol.) Most servers have a CompTIA ( NAT NAT editor. L2TP / IPSec clients can not be behind a NAT server, unless the VPN client and the VPN server to understand IPSec NAT Traversal (NAT-T). NAT-T is an ADI standard track? IKTF Tion which describes how IPsec can be used with NAT. Windows Server 2003, Microsoft L2TP/IPSec VPN client software L2TP/IPSec NAT-T update for Windows XP and Windows 2000 NAT-T support.
To understand why the VPN client and the server must understand NAT-T, you need to take? Ine the way IPSec encrypts packets and understand how NAT. Figure 7-5 shows part of the IPSec packet is protected encryptedwhich is almost everything. Decrypted is the source and destination IP address? Computer. When a NAT receives a packet to be transmitted to the Internet, it replaces the source IP address. This is not a problem for most IP traffic, because all responses will be directed to the NAT and NAT server can be the answer to the original sender computer and send it. However, the encrypted IPSec protected packet are validations that are calculated when the packet containing the IP address of the original source. Because NAT can not read and then re-encrypt the packet with a new A + exams (, the packet is interpreted by IPSec as corrupt or modified. This is why unmodified Windows 2000 computer can not sup? Performs a L2TP/IPSec VPN when NAT is part of the equation. Windows Server 2003 solves this problem with NAT-T. IPSec NAT-T encapsulates uses UDP packets and allows you to pass through a NAT. Internet Key Exchange (IKE) can detect if NAT-T is present and uses UDP-ESP encapsulation.
Windows Server 2003 supports NAT-T. The following Windows clients, updates or configured, also support NAT-T. You can use one of the following clients to create a VPN connection using L2TP/IPSeceven if they are behind a NAT serveras from the VPN server running Windows Server 2003:
review Tip a Windows 2000 server that has been made day with L2TP/IPSec can update? Do not become a routing and remote access VPN. The update is only for customers.
IPSec ESP requires origination authentication data packet, which provides evidence that the data was sent to a specific computer. It also requires data integrity, which is evidence that the data has not been modified in transit. In addition, IPSec ESP pro-vides replay protection, which is to protect against an attack that captures and then sends a data stream.
PPTP does not provide authentication data creation, data integrity, replay or CCNA ( protection.IPSec PPTP and ESP (using MPPE) provide packet data confidentiality (encryption).

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