Chapter 12 Configuring Inspection for Voice and Video Protocols

H.323 Inspection

H.323 Inspection Overview

H.323 inspection provides support for H.323 compliant applications such as Cisco CallManager and VocalTec Gatekeeper. H.323 is a suite of protocols defined by the International Telecommunication Union for multimedia conferences over LANs. The ASA supports H.323 through Version 6, including H.323 v3 feature Multiple Calls on One Call Signaling Channel.

With H.323 inspection enabled, the ASA supports multiple calls on the same call signaling channel, a feature introduced with H.323 Version 3. This feature reduces call setup time and reduces the use of ports on the ASA.

The two major functions of H.323 inspection are as follows:

•NAT the necessary embedded IPv4 addresses in the H.225 and H.245 messages. Because H.323 messages are encoded in PER encoding format, the ASA uses an ASN.1 decoder to decode the H.323 messages.

•Dynamically allocate the negotiated H.245 and RTP/RTCP connections.

How H.323 Works

The H.323 collection of protocols collectively may use up to two TCP connection and four to eight UDP connections. FastConnect uses only one TCP connection, and RAS uses a single UDP connection for registration, admissions, and status.

An H.323 client can initially establish a TCP connection to an H.323 server using TCP port 1720 to request Q.931 call setup. As part of the call setup process, the H.323 terminal supplies a port number to the client to use for an H.245 TCP connection. In environments where H.323 gatekeeper is in use, the initial packet is transmitted using UDP.

H.323 inspection monitors the Q.931 TCP connection to determine the H.245 port number. If the H.323 terminals are not using FastConnect, the ASA dynamically allocates the H.245 connection based on the inspection of the H.225 messages.

Note The H.225 connection can also be dynamically allocated when using RAS.

Within each H.245 message, the H.323 endpoints exchange port numbers that are used for subsequent UDP data streams. H.323 inspection inspects the H.245 messages to identify these ports and dynamically creates connections for the media exchange. RTP uses the negotiated port number, while RTCP uses the next higher port number.

The H.323 control channel handles H.225 and H.245 and H.323 RAS. H.323 inspection uses the following ports.

•1718—Gate Keeper Discovery UDP port

•1719—RAS UDP port

•1720—TCP Control Port

You must permit traffic for the well-known H.323 port 1719 for RAS signaling. Additionally, you must permit traffic for the well-known H.323 port 1720 for the H.225 call signaling; however, the H.245 signaling ports are negotiated between the endpoints in the H.225 signaling. When an H.323 gatekeeper is used, the ASA opens an H.225 connection based on inspection of the ACF and RCF nmessages.

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Cisco Systems ASA 5585-X, ASA 5505, ASA 5545-X, ASA 5555-X, ASA 5580 manual Inspection Overview, How H.323 Works, 12-3
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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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