My RelationshipViewer shows devices which are not real devices.

Document ID : KB000034626
Last Modified Date : 14/02/2018
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Introduction: 

My RelationshipViewer shows devices which are not real devices.

Question: 

Why does the RelationshipViewer show devices which are not real devices?

Answer: 

The topology agent may create “Device” objects to represent unknown parts of the network topology.  The “Device” objects have names of the form “Device_<IP address>_<port>” with the IP address and port of the switch that the Device connects to.

The topology agent creates the “Device” objects in the following circumstances:

  • When multiple nodes are seen downstream of a switch port and none of the downstream nodes are a SNMP enabled switch, it assumes that there must be a non-SNMP enabled switch downstream of the port and creates a device to represent it.   Sometimes the downstream nodes consists of virtual machines which means the port connects to the interface of a VM host.
  • When multiple nodes are seen between two SNMP enabled switches, it assumes that there must be an intervening non-SNMP enabled switch between them and creates a device to represent it.

 
These cases may be due to one or more of the following:

  • Incomplete SNMP data for the core network devices (switches and routers) in the topology.
  • “Dumb” switches or hubs in the network that are not SNMP capable. These devices may not even have an IP address.
  • Lack of information about VM hosts and virtual machines.  This is a limitation with the current topology solution and will be improved in the future.

 
In the case of incomplete SNMP data, please check the following:

  • All core network devices are SNMP enabled.  A network administrator may need to check this and determine the correct SNMP authentication credentials for the devices.
  • SNMP authentication profiles are defined to handle the core network devices.
  • The core network devices are included in discovery scopes.
  • The SNMP authentication profiles are mapped to the discovery scopes.
  • The discovery agent has successfully discovered the core network devices via SNMP and has assigned the correct SNMP authentication profile to the device.
  • The topology agent has successfully queried the device via SNMP.  You may need to check the support or log files to verify this.

 
Often the RCA/Topology RelationshipViewer will display devices that do not look like they are part of your network. These network elements usually have a name like Device_<IP>_N, where N is some integer. In this case, the relay device is strictly a representation of a port that a group of devices are connected to.  N is the port on an SNMP router or switch that this relay device represents. In theory, one router could have a relay device. This is not a common name of devices, and usually the name is based on the IP of a machine which is a real member of your network.
 
These machines are a synthetic inclusion into the topology. They are used to represent connective network elements that cannot be scanned by the topology_agents. There are some legitimate reasons that these elements cannot be scanned: scope restrictions, snmp credentials, non-snmp responsiveness.
 
If two sets of machines, defined by topology_agent scopes, can be shown to be connected, but the connecting switch or router is not included in the scopes, then the relationship_services will construct a synthetic node and add it to the list of discovered machines.
 
If a router, switch or similar device does not have snmp enabled, then the RCA/Topoloy services will not be able to correctly identify them. Often there are dumb hubs and relays in a network. These devices may have detectable MAC addresses, but nothing else about them can be discovered by the topology_agents. A dumb hub will not have a mac address associated with it if it is only operating on layer one. Do not expect any MAC information when viewing this device in Relationship Services. In these cases a synthetic node is generated as a place holder so that the relationship_services can make a usefully connected map.
 
If a switch or router is in the topology_agent scopes, but the probe has not been provided with useful snmp credentials, then the relationship_services may not construct useful relationships around this device. If the topology agent is unable to discern any relationship s with this device, it will exist as an unconnected node on the network.