Microsoft KB Archive/299999

= Network devices display incorrect connections in your Visio 2002 network diagram =

Article ID: 299999

Article Last Modified on 7/27/2006

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APPLIES TO


 * Microsoft Visio 2002 Professional Edition
 * Microsoft Visio Network Center
 * Microsoft Visio Enterprise Network Tools

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This article was previously published under Q299999





SYMPTOMS
In Microsoft Visio, when you add network devices to your network diagram based on your AutoDiscovery database, some devices may not show the correct connections to other devices. For example, when you connect devices on your diagram, a Cisco router may be incorrectly linked to another Cisco router, even though the router actually connects to a switch on your network.



CAUSE
This behavior occurs if all of the following conditions are true:
 * You are creating a layer 2 (data link) connectivity network diagram.
 * You attempt to add and connect Cisco network devices and non-Cisco network devices to your diagram.
 * The Cisco Discovery Protocol (CDP) is enabled on Cisco network devices when discovery is performed.

CDP is a proprietary protocol used by Cisco devices to assist in discovering the topology of the network. A Cisco device communicates with, and stores information about, Cisco devices that are directly connected to it (CDP neighbors). However, because CDP is specific to Cisco network devices, when a non-Cisco network device is directly connected to a CDP-enabled port, CDP traffic passes through the non-Cisco device until it finds another Cisco device. This creates an inaccurate database of &quot;directly&quot; connected neighbor information in the CDP database. As a result, this incorrect connectivity information is reflected in your Visio network diagram when you add and connect devices based on your AutoDiscovery database.



RESOLUTION
To work around this issue, disable CDP on any Cisco network device ports that directly connect Cisco network devices to non-Cisco network devices. After you disable CDP, perform another discovery of your network, create your network diagram, and then add and connect the network devices that you want.

For more information about CDP, visit the following Cisco Systems Web site:

http://www.cisco.com



STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the &quot;Applies to&quot; section.



MORE INFORMATION
The following are two scenarios that demonstrate the difference in the display of a layer 2 discovery operation when CDP is enabled versus when CDP is disabled.

Example 1
Cisco switch CsA, is directly connected to Cisco router CrB. The Cisco router, CrB, is connected to 3Com switch 3sC. The 3Com switch, 3sC, is directly connected to another Cisco router, CrD. With CDP enabled on Cisco routers CrB and CrD, a layer 2 discovery produces a displayed connection between the two routers. The 3Com switch, 3sC, does not show connectivity to the Cisco routers, CrB and CrD, and is therefore orphaned. If CDP is disabled on either of the Cisco routers, CrB or CrD, a layer 2 discovery produces a displayed connection that includes the 3Com switch 3sC. The connectivity is then displayed correctly as follows: Cisco router CrB - 3Com switch 3sC - Cisco router CrD.

Example 2
Dumb hub dhA is directly connected to Cisco switch CsB, Cisco router CrC, Rmon probe RpD, and workstation WsE. When CDP is enabled in Cisco switch CsB and Cisco router CrC, a layer 2 discovery produces a displayed connection between the switch CsB and router CrC. Rmon probe RpD and workstation WsE are not connected to any devices (and are therefore orphaned). Because dumb hub dhA is not discovered, it is not displayed. To correct this, disable CDP in either the switch CsB or router CrC. Layer 2 discovery then produces a display where all devices are correctly connected to a pseudo hub (a small 0 object with layer 2 connectors), and therefore no devices are orphaned. Again, dumb hub dhA does not appear because it is not discovered.

