XCCC: Multicast Conferencing May Not Work Over VPN Connection (293855)


The information in this article applies to:

  • Microsoft Exchange 2000 Conferencing Server
This article was previously published under Q293855

SYMPTOMS

You may not be able to join a multicast conference if you use a dial-up or virtual private network (VPN) connection. Additionally, you may receive the following error message in the video conferencing frame of your Web browser:
An audio video connection to the Exchange Conferencing Server could not be automatically established. Either client, server, or network capabilities could not be negotiated or the conference capacity may have been reached.

CAUSE

This behavior may occur if a Windows 2000 client has multiple network connections configured, such as all of the following:
  • Local area network (LAN)Point-to-Point Protocol (PPP)Internet service provider (ISP)Point-to-Point Tunneling Protocol (PPTP) over the PPP connection to a corporate network
In this scenario, the multicast packets may not be sent over the correct network adapter.

WORKAROUND

Provided that the conferencing resource is H.323-enabled, you can generally join the conference, and send and receive audio and video, through the H.323 standard.

NOTE: The Cisco VPN client is incompatible with H.323.

MORE INFORMATION

Although it may be possible to correct this issue, multicast conferencing is neither a tested nor supported environment. Any issues that occur because of multicasting over a dial-up or VPN connection are not supported by Microsoft.

Before a client computer establishes a dial-up (VPN) connection, its routing table may look similar to the following: 

===========================================================================
Active Routes:
Network Destination        Netmask          Gateway       Interface  Metric
          0.0.0.0          0.0.0.0      199.199.1.1    199.199.1.98	  1
        127.0.0.0        255.0.0.0        127.0.0.1       127.0.0.1	  1
      199.199.1.0    255.255.255.0     199.199.1.98    199.199.1.98	  1
     199.199.1.98  255.255.255.255        127.0.0.1       127.0.0.1	  1
    199.199.1.255  255.255.255.255     199.199.1.98    199.199.1.98	  1
        224.0.0.0        224.0.0.0     199.199.1.98    199.199.1.98	  1
  255.255.255.255  255.255.255.255     199.199.1.98    199.199.1.98	  1
Default Gateway:       199.199.1.1
===========================================================================

After a VPN connection is made to the server, its routing table looks similar to this: 

===========================================================================
Active Routes:
Network Destination        Netmask          Gateway       Interface  Metric
          0.0.0.0          0.0.0.0   157.54.128.222  157.54.128.222	  1
          0.0.0.0          0.0.0.0      199.199.1.1    199.199.1.98	  2
        127.0.0.0        255.0.0.0        127.0.0.1       127.0.0.1	  1
   157.54.128.222  255.255.255.255        127.0.0.1       127.0.0.1	  1
   157.54.128.226  255.255.255.255   157.54.128.222  157.54.128.222	  1
   157.54.255.255  255.255.255.255   157.54.128.222  157.54.128.222	  1
      199.199.1.0    255.255.255.0     199.199.1.98    199.199.1.98	  1
     199.199.1.98  255.255.255.255        127.0.0.1       127.0.0.1	  1
    199.199.1.255  255.255.255.255     199.199.1.98    199.199.1.98	  1
        224.0.0.0        224.0.0.0   157.54.128.222  157.54.128.222	  1
        224.0.0.0        224.0.0.0     199.199.1.98    199.199.1.98	  1
  255.255.255.255  255.255.255.255     199.199.1.98    199.199.1.98	  1
Default Gateway:    157.54.128.222
===========================================================================

NOTE: In this case, the PPP adapter (157.128.222) becomes the default route, as demonstrated by the metric of 1. The multicast routes (224.0.0.0) both have a metric of 1. This means that the multicast traffic can go out either interface, and it generally uses the original route. However, the original route is not what you want in this case, because this interface has no multicast connectivity to the Exchange Conferencing Server computer.

The third-party products that are discussed in this article are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, regarding the performance or reliability of these products.
Modification Type:MinorLast Reviewed:4/25/2005
Keywords:kberrmsg kbprb KB293855
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