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Cisco ASA Series CLI Configuration Guide
Chapter 1 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.
Summary of Contents for 5505 - ASA Firewall Edition Bundle
Page 28: ...Glossary GL 24 Cisco ASA Series CLI Configuration Guide ...
Page 61: ...P A R T 1 Getting Started with the ASA ...
Page 62: ......
Page 219: ...P A R T 2 Configuring High Availability and Scalability ...
Page 220: ......
Page 403: ...P A R T 2 Configuring Interfaces ...
Page 404: ......
Page 499: ...P A R T 2 Configuring Basic Settings ...
Page 500: ......
Page 533: ...P A R T 2 Configuring Objects and Access Lists ...
Page 534: ......
Page 601: ...P A R T 2 Configuring IP Routing ...
Page 602: ......
Page 745: ...P A R T 2 Configuring Network Address Translation ...
Page 746: ......
Page 845: ...P A R T 2 Configuring AAA Servers and the Local Database ...
Page 846: ......
Page 981: ...P A R T 2 Configuring Access Control ...
Page 982: ......
Page 1061: ...P A R T 2 Configuring Service Policies Using the Modular Policy Framework ...
Page 1062: ......
Page 1093: ...P A R T 2 Configuring Application Inspection ...
Page 1094: ......
Page 1191: ...P A R T 2 Configuring Unified Communications ...
Page 1192: ......
Page 1333: ...P A R T 2 Configuring Connection Settings and QoS ...
Page 1334: ......
Page 1379: ...P A R T 2 Configuring Advanced Network Protection ...
Page 1380: ......
Page 1475: ...P A R T 2 Configuring Modules ...
Page 1476: ......
Page 1549: ...P A R T 2 Configuring VPN ...
Page 1550: ......
Page 1965: ...P A R T 2 Configuring Logging SNMP and Smart Call Home ...
Page 1966: ......
Page 2059: ...P A R T 2 System Administration ...
Page 2060: ......
Page 2098: ...1 8 Cisco ASA Series CLI Configuration Guide Chapter 1 Troubleshooting Viewing the Coredump ...
Page 2099: ...P A R T 2 Reference ...
Page 2100: ......