Path analysis (Network Explorer –> Topology –> Path Analysis) allows tracing a L3 path across a network of any scale, subject only to the restriction that NetMRI must discover and manage both the source and destination devices. The devices forming the endpoints of the path can be any of the following:

Routers
VRF instances inside routers
Switch-Routers, including VLANs

In the Network Explorer pages, you can also use a drag-and-drop interface to define the source and destination values for a Path Analysis.
You can also perform path analysis for multiple paths from the same source location, and you can define the maximum number of calculated paths from a device.
Path Analysis also enables a powerful feature called Start From Device, in which the only value needed for a path trace is the destination IP address or device's FQDN. Then, choose any device in the network to start the path trace.

Note: Path Analysis does not support L3 path traces across protocols that are not directly supported by NetMRI, including MPLS, MPLS-TE and GLBP. In cases where only a partial path can be traced because it terminates in a hop that is an endpoint for one of these protocols, you can use the Start From Device feature to resume the trace from the hop where the MPLS or GLBP tunnel terminates.

NetMRI calculates paths based on collected routing table information, and are determined in the following order:

Directly connected
Longest subnet prefix
Administrative distance

NetMRI does not collect administrative distance from managed devices; when necessary, path calculations rely on the Routing Distance values defined in the NetMRI appliance (see Defining Path Analysis Settings for more information).
You may choose to have NetMRI calculate a path by specifying only a destination device. To perform a basic Path Analysis, do the following:

Open Network Explorer –> Topology.

Choose a Device Group from the Select Device Groups menu in the right pane.
In the left panel accordion menu, click Path Analysis.

A blank Topology Viewer panel appears in the center panel, with Source, Source Network View and Destination fields on the top.

Enter the Source and Destination values for the two devices whose common path(s) you want to trace. (You can press the Tab key to move between the Source, Destination and the Start button.) As you enter the IP values, NetMRI evaluates the entry to ensure the value is part of the chosen device group. If the value is correct, the device value displays in grey. If either value is incorrect for any reason, you will see an Invalid Source or Invalid Destination tooltip and the field will be outlined in red.
Choose the network view for the network you are tracing from the Source Network View dropdown list. If the path is known to be within the globally routed network, select the Network 1 network view. If there is only one network view being managed by NetMRI, this field will not appear.

If you choose an incorrect network view, you will receive a Path start device could not be determined error.

Choose Start from the drop-down menu.

After a moment, the topology map appears for the chosen values.

The system saves the Path Analysis instance you just created under the Path Analysis menu.
After the path analysis completes, if a path does not complete because of intermediate devices that are endpoints for an MPLS encapsulated tunnel (or from other similar protocols), select the device in the path from which the VPN terminates, and continue the path analysis form there using the Continue Path Analysis From Device option. This option is similar to the Start from Device drop-down menu option in the center pane.

Simultaneous Path Calculations

In a large network, more than one possible path my exist between two devices. You can control the number of path calculations performed for the same Source/Destination pair. The default number of simultaneous path calculations is 2, with a maximum value of 10. Go to Settings icon –> General Settings –> Path Analysis and edit the Number of Calculated Paths setting. Avoid setting this value to too high a number, as multiple active path calculations can affect performance.

Resuming a Path from a Different Source Device

When performing path analysis, the path may be incomplete due to the following reasons:

One or more devices on the path is incompletely discovered;
A segment of the network path is comprised of an encrypted tunnel.

The Start from Device feature for Path Analysis enables the resumption of a trace from any selected point elsewhere in the network. For example, a device might appear in the network that isn't fully discovered by NetMRI; once it is, and assuming it is covered by licensing, you can resume the path analysis from that device and continue on to finish the trace. You may have to wait for a brief period before the device is fully discovered and licensed, and the device has its routing tables added to the NetMRI database.
If the network provides for two Zones separated by a VPN, you can trace up to the endpoint of the first part of the path, note the device name where the VPN tunnel terminates, and use that device to resume the trace to the same Destination device. Do the following: