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D14049.05
February 2009
Grey Headline
(continued)
TANDBERG
VIDEO COMMUNICATIONS SERVER
ADMINISTRATOR GUIDE
Introduction
Getting started
Overview and
status
System
configuration
VCS
configuration
Zones and
neighbors
Call
processing
Bandwidth
control
Firewall
traversal
Appendices
Applications
Maintenance
Firewall traversal overview
The purpose of a firewall is to control the IP traffic entering your network. Firewalls will generally
block unsolicited incoming requests, meaning that any calls originating from outside your network
will be prevented. However, firewalls can be configured to allow outgoing requests to certain
trusted destinations, and to allow responses from those destinations. This principle is used by
TANDBERG’s Expressway™ solution to enable secure traversal of any firewall.
The Expressway™ solution consists of:
a TANDBERG VCS Expressway or TANDBERG Border Controller located outside the firewall on the
1.
public network or in the DMZ, which acts as the firewall traversal server
a TANDBERG VCS Control, TANDBERG Gatekeeper, MXP endpoint or other traversal-enabled
2.
endpoint located in a private network, which acts as the firewall traversal client.
The two systems work together to create an environment where all connections between the two
are outbound, i.e. established from the client to the server, and thus able to successfully traverse
the firewall.
How does it work?
The traversal client constantly maintains a connection via the firewall to a designated port on the
traversal server. This connection is kept alive by the client sending packets at regular intervals to
the server. When the traversal server receives an incoming call for the traversal client, it uses this
existing connection to send an incoming call request to the client. The client then initiates the
necessary outbound connections required for the call media and/or signaling.
This process ensures that from the firewall’s point of view, all connections are initiated from the
traversal client inside the firewall out to the traversal server.
!
In order for firewall traversal to function correctly, the VCS Expressway must have one
traversal server zone configured on it for each client system that is connecting to it (this
does not include traversal-enabled endpoints which register directly with the VCS
Expressway; the settings for these connections are configured in a different way). Likewise, each
VCS client must have one traversal client zone configured on it for each server that it is connecting
to. The ports and protocols configured for each pair of client-server zones must be the same. (See
Quick guide to VCS traversal client - server configuration
for a summary of the configuration on each
system.) Because the VCS Expressway listens for connections from the client on a specific port, we
recommend that you create the traversal server zone on the VCS Expressway before you create the
traversal client zone on the VCS Control.
The VCS Expressway has all the functionality of a VCS Control (including being able to act as a
firewall traversal client). However, its main feature is that it can act as a firewall traversal server for
other TANDBERG systems and any traversal-enabled endpoints that are registered directly to it. It
can also provide STUN Discovery and STUN relay services to endpoints with STUN clients. These
features are enabled as follows:
In order for the VCS Expressway to act as a firewall traversal server for TANDBERG systems, you
•
must create and configure a new traversal server zone on the VCS Expressway for every system
that is its traversal client. See
Configuring the VCS as a traversal serve
r
for full instructions.
In order for the VCS Expressway to act as a firewall traversal server for traversal-enabled
•
endpoints (i.e. TANDBERG MXP endpoints and any other endpoints that support the ITU
H.460.18 and H.460.19 standards), no additional configuration is required. See
Configuring
traversal for endpoints
for more information on the options available.
To enable STUN Discovery and STUN Relay services, see
•
STUN services
.
To reconfigure the default ports used by the VCS Expressway, see
•
Configuring traversal server
ports
.
Your VCS can act as a firewall traversal client on behalf of SIP and H.323 endpoints registered to it,
and any gatekeepers that are neighbored with it.
In order to act as a firewall traversal client, the VCS must be configured with information about the
system(s) that will be acting as its firewall traversal server. See the section on
Configuring the VCS
as a traversal client
for full details on how to do this.
In most cases, you will use a VCS Control as a firewall traversal client. However, a VCS
Expressway can also act as a firewall traversal client.
The firewall traversal server used by the VCS client can be a TANDBERG VCS Expressway, or
(for H.323 only) a TANDBERG Border Controller.
About Expressway™
VCS as a firewall traversal client
VCS as a firewall traversal server
