![]() The network administrator prefers to use a connection-oriented protocol such as TCP.ESP (IP protocol 50) is not allowed to pass, and as a result encrypted traffic does not traverse.UDP port 500 is blocked, resulting in incomplete IKE negotiations.IPSec over TCP is an important feature used in scenarios where: Disabling NAT-T for Remote-Access TunnelsĬhicago(config)# crypto dynamic-map outside_dyn_map 20 set nat-t-disable If NAT-T is globally enabled, but if you do not want to use NAT-T for the remote-access tunnel, you can use the crypto dynamic-map set nat-t-disable option, the command syntax for which is as follows:Ĭrypto dynamic-map map-name seq-num set nat-t-disableĮxample 16-28 illustrates how to disable NAT-T for a dynamic map, called outside_dyn_map.Įxample 16-28. The security appliance sends periodic keepalives to keep them active even if there is no data flowing over the VPN connection. NAT-T keepalives are used to make sure that a NAT or PAT device does not age out the VPN tunnel on UDP port 4500. If you don't specify the keepalives range, Cisco ASA uses 20 seconds as the default. Here, the keepalives range is between seconds. The command syntax to enable NAT-T globally on Cisco ASA is as follows: As soon as the VPN peers discover that they are NAT-T capable and a NAT/PAT device resides between them, they switch over to UDP port 4500 for the rest of tunnel negotiations and data encapsulation. If both conditions are true, the VPN client tries to connect to the security appliance using UDP port 500 for IKE negotiations. A NAT or PAT device exists between VPN peers.NAT-T is dynamically negotiated if the following two conditions are met: NAT-T, currently an IETF draft, is a feature that encapsulates the ESP packets into UDP port 4500 packets. The sections that follow cover these options in greater detail. To remedy this problem, Cisco ASA offers three different options: Because IPSec uses ESP (IP protocol 50), which does not have Layer 4 information, the NAT device is usually incapable of translating the encrypted packets going over the VPN tunnel. In many network topologies, the VPN clients reside behind a SOHO NAT/PAT device that inspects the Layer 4 port information for address translation. The sections that follow cover these features in more detail. ![]() Cisco ASA provides many advanced features to suit your remote-access VPN implementations.
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