If you choose the Permit or Block options for a filter action, there is nothing left to configure. In fact, you never need more than one filter action for each of the Permit and Block options. There are several additional settings to consider when you configure a filter action to negotiate security. Otherwise, clients without IPSec will be denied access to the server.
Generally, this setting is enabled only when Active Directory is used to deploy IPSec configuration settings to all networked computers. You should use the Filter Action Wizard to configure filter actions whenever possible, because configuring integrity and encryption settings can be complicated. The IP Traffic Security page of the wizard enables you to specify the protection suites associated with the filter action.
By selecting Custom, you can configure the specific algorithms you want to use for integrity and encryption, including the option to use MD5 for integrity instead of the default SHA1, and standard Data Encryption Standard DES for encryption instead of the default 3DES. Selecting Custom also gives you the option to change the default settings for Quick Mode key regeneration by specifying a certain amount of time or a specific amount of data.
If you do not select either check box, IPSec will automatically initiate Quick Mode negotiation every hour or for every megabytes MB of data transferred. The more frequently a session key is regenerated, the harder it is for an attacker to decrypt your traffic. However, regenerating session keys adds performance overhead and decreases network throughput.
In fact, regenerating session keys will have a noticeable negative impact only if you configure the session keys to be regenerated extremely frequently—say every few seconds. You can configure multiple protection suites for a single filter action. IPSec will start negotiations with the first security method in the list. If that fails, IPSec will work its way down the list until a connection is successfully negotiated or until the end of the list is reached.
You should order the security methods from most secure to least secure. This will ensure that IPSec will negotiate the most secure connection possible with clients and fall back to less secure communications only when negotiations fail. As mentioned in Lesson 1, it is the IPSec client, also referred to as the initiator , that determines the order in which the protection suites are evaluated. Selecting this check box specifies that you want to renegotiate new master key keying material each time a new session key is required.
Basically, this improves the security of the connection by making it more difficult for an attacker to decrypt the communications. However, it requires additional negotiations between the client and server, which reduces performance. Using Session Key PFS discourages only those attackers who use brute- force methods to decrypt traffic, which is an extremely impractical task. Therefore, you should enable PFS only for organizations that have the highest possible security requirements.
Click the Manage Filter Actions tab. You can then click the Add, Edit, or Remove buttons. Permit, obviously, allows traffic to be forwarded. Request Security attempts to negotiate with a client that submits an unsecured connection request.
If the client and server cannot agree on a set of IPSec settings, an unsecured connection will be established.
Require Security also attempts to negotiate an authenticated and encrypted connection with the client, but it will drop the connection if negotiation fails. You can specify only one IP filter list and one filter action per rule. If the rule pertains to traffic traveling between networks across an IPSec tunnel, you should provide the IP address of the tunnel endpoint. This does not conflict with your ability to add IP filter lists; you can configure an endpoint and apply the rule only to traffic on a specific subnet within the destination network accessible through the IPSec tunnel.
The default response rule is used to configure the computer to respond to requests for secure communication when no other rules match the traffic. If an active policy does not have a rule defined for a computer that is requesting secure communication, the default response rule is applied and security is negotiated. For example, when Computer A communicates securely with Computer B, and Computer B does not have an inbound filter defined for Computer A, the default response rule is used.
The default response rule cannot be deleted, but it can be deactivated. It is activated by default for all policies. To avoid the security risks related to unwanted security negotiations, you can disable the default response rule. Attackers can use the IPSec negotiation process enabled by the default response rule to obtain information about the computer through the security negotiation. A skilled Internet attacker can construct specific security negotiation requests to query and obtain the name of the client, trust relationships, and other settings that are configured in the default response rule.
For example, if you use Kerberos as the authentication method for the default response rule, an attacker can query the Kerberos identity of the client. The query results will provide the attacker with the computer name and domain hierarchy, such as username contoso.
If you use certificate-based authentication as the authentication method for the default response rule, the attacker might be able to obtain the names of the PKI trusted root CAs that are configured for the default response rule. You must also configure the authentication method. Edit the new policy properties, and click the Rules tab.
Double click the newly created filter rule and select Security Methods:. Choose these settings. Save all configurations on both the Controller and WinServer and reboot all machines.
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