Chapter 6 Configuring NAT (ASA 8.2 and Earlier)

Using Static NAT

Step 6 Specify the mapped IP address by clicking one of the following:

•Use IP Address

Enter the IP address or click the ... button to choose an IP address that you already defined in ASDM.

Specify the address and subnet mask using prefix/length notation, such as 10.1.1.0/24. If you enter an IP address without a mask, it is considered to be a host address, even if it ends with a 0.

•Use Interface IP Address

The real and mapped addresses must have the same subnet mask.

Step 7 (Optional) To use static PAT, check Enable Port Address Translation (PAT).

a.For the Protocol, click TCP or UDP.

b.In the Original Port field, enter the real port number.

c.In the Translated Port field, enter the mapped port number.

Step 8 (Optional) Enter a description in the Description field.

Step 9 (Optional) To enable translation of addresses inside DNS replies, expand the Connection Settings area, and check the Translate the DNS replies that match the translation rule check box.

If your NAT rule includes the real address of a host that has an entry in a DNS server, and the DNS server is on a different interface from a client, then the client and the DNS server need different addresses for the host; one needs the mapped address and one needs the real address. This option rewrites the address in the DNS reply to the client. The mapped host needs to be on the same interface as either the client or the DNS server. See the “DNS and NAT” section on page 6-14for more information.

Step 10 (Optional) To enable connection settings, expand the Connection Settings area, and set one or more of the following options:

Note You can also set these values using a security policy rule. To set the number of rate intervals maintained for host statistics, on the Configuration > Firewall > Threat Detection > Scanning Threat Statistics area, choose 1, 2, or 3 from the User can specify the number of rate for Threat Detection Host drop-down list. Because host statistics use a lot of memory, reducing the number of rate intervals from the default of 3 reduces the memory usage. By default, the the Firewall Dashboard Tab shows information for three rate intervals, for example, for the last 1 hour, 8 hours, and 24 hours. If you set this keyword to 1, then only the shortest rate interval statistics are maintained. If you set the value to 2, then the two shortest intervals are maintained. If you set them in both places, then the ASA uses the lower limit. For TCP sequence randomization, if it is disabled using either method, then the ASA disables TCP sequence randomization.

•Randomize sequence number—With this check box checked (the default), the ASA randomizes the sequence number of TCP packets. Each TCP connection has two ISNs: one generated by the client and one generated by the server. The ASA randomizes the ISN of the TCP SYN passing in both the inbound and outbound directions.

Randomizing the ISN of the protected host prevents an attacker from predicting the next ISN for a new connection and potentially hijacking the new session.

TCP initial sequence number randomization can be disabled if required. For example:

–If another in-line firewall is also randomizing the initial sequence numbers, there is no need for both firewalls to be performing this action, even though this action does not affect the traffic.

–If you use eBGP multi-hop through the ASA, and the eBGP peers are using MD5. Randomization breaks the MD5 checksum.

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Cisco Systems ASA 5580, ASA 5505, ASA 5545-X, ASA 5555-X, ASA 5585-X, ASA Services Module manual Use IP Address
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ASA Services Module, ASA 5555-X, ASA 5545-X, ASA 5585-X, ASA 5580 specifications

Cisco Systems has long been a leader in the field of network security, and its Adaptive Security Appliance (ASA) series is a testament to this expertise. Within the ASA lineup, models such as the ASA 5505, ASA 5580, ASA 5585-X, ASA 5545-X, and ASA 5555-X stand out for their unique features, capabilities, and technological advancements.

The Cisco ASA 5505 is designed for small businesses or branch offices. It provides essential security features such as firewall protection, flexible VPN capabilities, and intrusion prevention. The ASA 5505 supports a user-friendly interface, allowing for straightforward management. Its built-in threat detection and prevention tools provide a layered defense, and with scalability in mind, it can accommodate various expansion options as organizational needs grow.

Moving up the line, the ASA 5580 delivers greater throughput and advanced security features. This model is suited for medium to large enterprises that require robust protection against increasingly sophisticated threats. Its multi-core architecture allows it to manage high volumes of traffic seamlessly while maintaining excellent performance levels. The ASA 5580 also supports application-layer security and customizable access policies, making it highly adaptable to diverse security environments.

The ASA 5585-X further enhances Cisco's security offerings with advanced malware protection and extensive security intelligence capabilities. It incorporates next-generation firewall features, including context-aware security, and supports advanced threat detection technologies. This model is ideal for large enterprises or data centers that prioritize security while ensuring uninterrupted network performance and availability.

For enterprises requiring a balance of performance and security, the ASA 5545-X presents a compelling option. This model features scalable performance metrics, high availability, and integrated advanced threat protection. Coupled with advanced endpoint protection and detailed monitoring capabilities, the ASA 5545-X enables organizations to manage their security posture effectively.

Lastly, the ASA 5555-X blends cutting-edge technologies with strong security infrastructures. It boasts high throughput and the ability to execute deep packet inspections. Its sophisticated architecture supports threat intelligence feeds that provide real-time security updates, making it a powerful tool against modern threats.

Each of these Cisco ASA models brings specific advantages to varied environments. Their integrative capabilities enable businesses to enhance their security postures while benefiting from seamless scalability and management. As cybersecurity threats evolve, these advanced appliances play a vital role in protecting valuable digital assets.
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