Performing Path Traces
About Path Trace
With Path Trace, the controller reviews and collects network topology and routing data from discovered devices. Then it uses this data to calculate a path between two hosts or Layer 3 interfaces. Optionally, you can choose to collect interface and QoS statistics for a path. You can use the information gathered through Path Trace to monitor and debug traffic paths that are distributed among the various devices throughout your network.
You perform these tasks by running a path trace between two nodes in your network. The two nodes can be a combination of wired or wireless hosts and/or Layer 3 interfaces. In addition, you can specify the protocol for the controller to use to establish the path trace connection, either TCP or UDP.
At every node in the path, the controller reports information about the device and path. For example, if a Layer 2 protocol is used to discover a node, the controller reports that the path is a switched path and labels it as Switched. If the controller detects load balancing decisions being made on a discovered device, it reports the path as an ECMP path and labels it as ECMP. Path trace can identify the following information about the devices and paths:
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HSRP
-
SVI
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Layer 2
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Layer 2 Port Channel
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Layer 3 Routing Protocol
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ECMP/TR
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Netflow
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ECMP over SVI
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Subinterface
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EIGRP
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Level 3 Recursive Loop
For nodes that are unknown devices within a path trace (usually non-Cisco devices), the controller calculates the path between the unknown devices starting from the last known Cisco device (from the Host Source IP) to the next, neighboring Cisco device (sometimes the Destination Source IP). The collected IP address data about the unknown device is then sent from this neighboring Cisco device to the controller to calculate the trace path. The unknown device is displayed in the controller's GUI as a question mark (?).
![]() Note | In certain circumstances, a path trace may flow between one of two (or more) devices. To determine which device actually received the flow for the path trace, the controller reads the NetFlow configurations and records on the devices (if they exist). By reading this data from the devices, the controller can determine the likelihood of the actual path. |
To access the Path Trace window, from the Navigation pane, click Path Trace.

Callout Number |
Name |
Description |
---|---|---|
1 |
Toolbar |
Provides the following functions:
|
2 |
In-progress, Active, and Completed Path Traces |
In-progress path traces are those that have not completed yet. Active path traces are completed and being updated once every 30 seconds. Completed path traces are calculated once and are not updated. |
3 |
Trace Results Graphical Display |
Displays the results of the path trace. For information, see Understanding Path Trace Results. |
4 |
Reversed Results Graphical Display |
Shows the path trace in reverse order, from the destination host to the source host. For information, see Understanding Path Trace Results. |
5 |
Trace Results Device Details |
Provides detailed information about the devices along the path. For information, see Understanding Path Trace Results. |
6 |
View in Topology button |
Displays the trace results in the Topology window. |
- Path Trace Support
- Path Trace Protocols and Network Connections
- Understanding Path Trace Results
- Understanding the Interface Statistics Retrieved During a Path Trace
- Understanding the QoS Statistics Retrieved During a Path Trace
Path Trace Support
![]() Note | If the controller can not complete a path trace for the selected hosts or interfaces, it displays the results of a partial trace. |
Path Trace Protocols and Network Connections
The following table describes the supported device protocols and network connections (physical, wireless, and virtual) for a Cisco APIC-EM path trace.
![]() Note | For detailed information about protocol, wireless, and AP support by platform and scenario, see the Release Notes for the Cisco Application Policy Infrastructure Controller Enterprise Module. |
Understanding Path Trace Results
After you run a path trace, the results are displayed in the Trace Results Graphical Display pane.
Path Traces Pane
The Path Traces pane lists the path traces in one of three categories:
-
IN PROGRESS— Path is currently being calculated. No results to show yet.
-
ACTIVE—A path has been calculated and will be refreshed every 30 seconds. Statistics may also be collected periodically.
-
COMPLETED—The path has been calculated one time and is not being refreshed. However, statistics may still be collected periodically.
Trace Results Graphical Display
At the top of the Trace Results Graphical Display pane, the toolbar provides buttons for adjusting the path trace display.
Name 1 |
Description |
---|---|
View Small |
Minimizes the trace results to view the details better. |
Show Reverse |
Displays the trace results from the host destination IP to the host source IP. The reverse path trace graphic is displayed directly below the original path trace. The reverse path trace details are displayed to the right of the original path trace details. |
Scroll Lock |
Locks the scrolling of the path trace and reverse path trace details windows. (Available when Show Reverse is enabled.) |
Show Duplicate Devices |
Displays or hides duplicate devices within a path trace. |
View in Topology |
Opens the Topology window and highlights the path trace results in your network topology. For more information about using the Topology window, see About Topology. |
The controller graphically displays the path direction and the devices and networks that the path traverses. The following information is also provided:
-
Hosts and devices (including their IP addresses) on the path trace between the source (host A) and destination (host B).
-
Link Source—Whether the path source between devices is either Switched, STP, ECMP, Routed, Trace Route, or other source type.
![]() Note | Clicking an individual device in the path trace highlights the device in the Trace Results Device Details area. |
Trace Results Device Details
You can review the detailed information displayed for each device in the path trace.
Name |
Description |
||
---|---|---|---|
IP |
IP address of the device. |
||
Type |
Wired or wireless device (access point, switch, or router). |
||
Link Source |
Information about the link between two devices (source and destination). Link information is based on the configuration of the source device.
|
||
Tunnels |
CAPWAP data (wireless) or mobility tunneling
|
||
Ingress interface |
Ingress interface of the device for the path trace (physical or virtual). For example, a physical ingress interface is GigabitEthernet1/0/1 and a virtual ingress interface is GigabitEthernet1/3 [Vlan1]. If statistics were gathered for this path trace, clicking the View Stats button displays the interface or QoS statistics. For information, see Understanding the Interface Statistics Retrieved During a Path Trace or Understanding the QoS Statistics Retrieved During a Path Trace. |
||
Egress interface |
Egress interface of the device for the path trace (physical or virtual). For example, a physical interface is GigabitEthernet1/0/2 and a virtual ingress interface is GigabitEthernet1/4 [Vlan2]. If statistics were gathered for this path trace, clicking the View Stats button displays the interface or QoS statistics. For information, see Understanding the Interface Statistics Retrieved During a Path Trace or Understanding the QoS Statistics Retrieved During a Path Trace. |
||
Accuracy note |
If there is uncertainty about the path trace on a segment between devices, path trace displays a note that indicates the accuracy of the computed path as a percentage. For example, 10 percent would indicate lower accuracy than 90 percent. Place your cursor over the note to view suggestions of corrective actions to take to improve the path trace accuracy. For example, you may be prompted to enter port values and run the path trace again. |
Understanding the Interface Statistics Retrieved During a Path Trace
When you perform a path trace, you can collect interface statistics that show how the interfaces are performing. In this way, you can monitor the effect of the QoS policies on the network and make any changes, if necessary. The following table lists the interface statistics that are retrieved.
Parameter |
Description |
---|---|
Admin Status |
Administrative status of the interface:
|
Input Packets |
Number of packets being received on the interface. |
Input Queue Drops |
Number of packets dropped from the input queue due to the queue reaching its maximum threshold. |
Input Queue Max Depth |
Maximum number of packets that the input queue can hold before it must start dropping packets. |
Input Queue Count |
Number of packets in the input queue. |
Input Queue Flushes |
Number of packets dropped due to Selective Packet Discard (SPD). SPD is a mechanism that quickly drops low priority packets when the CPU is overloaded in order to save some processing capacity for high priority packets. |
Input Rate (bps) |
Number of bits per second at which packets are entering the interface. |
Operational Status |
Operational status of the interface:
|
Output Drop |
Number of packets dropped from the output queue due to the queue reaching its maximum threshold. |
Output Packets |
Number of packets leaving the interface. |
Output Queue Count |
Number of packets in the output queue. |
Output Queue Depth |
Maximum number of packets that the output queue can hold before it must start dropping packets. |
Output Rate (bps) |
Number of bits per second at which packets are leaving the interface. |
Refreshed At |
Date and time that the current statistics were gathered. |
Understanding the QoS Statistics Retrieved During a Path Trace
When you perform a path trace, you can collect QoS statistics that show how the QoS policies are performing. The only interface statistics included in the QoS statistics are those for the border router egress interface. Collecting QoS statistics helps you to monitor the effect of the QoS policies on your network devices and make any changes, if necessary. The following table lists the QoS Statistics that are retrieved.
Parameter |
Description |
---|---|
Policy Name |
Drop-down list of policy names that QoS statistics have been collected about. |
Class Map Name |
Name of the class map. |
Num of Bytes |
Average number of bytes forwarded by the queue. |
Offered Rate |
Traffic rate offered for that particular traffic. |
Queue Bandwidth (bps) |
Rate (bps) at which the queue can process packets. |
Queue Total Drops |
Number of packets dropped from the queue due to the queue reaching its maximum threshold. |
Drop Rate |
Number of bits per second at which packets are being dropped from the queue. |
Num of Packets |
Number of packets that the queue can hold. |
Queue Depth |
Maximum number of packets that the queue can hold before it must start dropping packets. |
Queue No Buffer Drops |
Number of times that packets were dropped due to not enough buffer allocated. |
Refreshed At |
Date and time that the current statistics were gathered. |
Performing a Path Trace
You can perform a path trace between two nodes in your network. The two nodes may be two hosts and/or Layer 3 interfaces.
![]() Note | The path trace application may display accuracy notes. Accuracy notes are red boxes that appears on a node or path segment indicating the accuracy of the computed path as a percentage. Place your cursor over the note to view suggestions of corrective actions to take to improve the path trace accuracy. For example, you may be prompted to enter port values and run the path trace again. |
Make sure that you have devices in your inventory. If not, discover devices using the Discovery function.
Ensure that the controller has SSH or Telnet access to the devices.
Step 1 | In the Navigation pane, click Path Trace. | ||
Step 2 | From the path trace toolbar, click Start new Path Trace. | ||
Step 3 | In the Source field,
enter the IP address of the host or the Layer 3 forwarding interface where you
want the trace to start.
If you enter the device IP address manually, you need to select the device from the list and then the interfaces for that device. | ||
Step 4 | In the Destination
field, enter the IP address of the host or Layer 3 forwarding interface where
you want the trace to end.
If you enter the device IP address manually, you need to select the device from the list and then the interfaces for that device. | ||
Step 5 | (Optional)To configure source and destination ports or protocols, click More Options. | ||
Step 6 | (Optional)In the Source Port field, enter the port number of the host where you want the trace to end. | ||
Step 7 | (Optional)In the Destination Port field, enter the port number of the host where you want the trace to end. | ||
Step 8 | (Optional)In the Protocol field, choose either tcp or udp from the drop-down menu for the Layer 4 path trace protocol. | ||
Step 9 | (Optional)To configure the path trace to refresh every 30 seconds, check the Periodic Refresh (30 sec) check box. | ||
Step 10 | (Optional)To configure the path trace
to collect additonal statistics, check the Stats check
box and any of the following check boxes, as desired:
| ||
Step 11 | Click Start Trace.
Review the path trace output. For more information, see Understanding Path Trace Results. | ||
Step 12 | To view the
path trace in the
Topology window. Click
View
in Topology.
The
Topology window opens with the path trace highlighted
in your network. For more information about the
Topology window, see
About Topology.
|
Collecting QoS and Interface Statistics in a Path Trace
You can perform a path trace between two nodes in your network and collect interface and/or QoS statistics about the devices in the path.
![]() Note | The path trace application may display accuracy notes. Accuracy notes are red boxes that appears on a node or path segment indicating the accuracy of the computed path as a percentage. Place your cursor over the note to view suggestions of corrective actions to take to improve the path trace accuracy. For example, you may be prompted to enter port values and run the path trace again. |
Make sure that you have devices in your inventory. If not, discover devices using the Discovery function.
Step 1 | In the Navigation pane, click Path Trace. | ||
Step 2 | From the path trace toolbar, click Start new Path Trace. | ||
Step 3 | In the Source field, enter the IP address of the host
or the Layer 3 forwarding interface where you want the trace to start.
To list the Layer 3 forwarding interfaces for a device, enter the device name or IP address followed by a colon ":". All interfaces with IP addresses on the device are displayed. | ||
Step 4 | In the Destination field, enter the IP address of the
host or Layer 3 forwarding interface where you want the trace to end.
To list the Layer 3 forwarding interfaces for a device, enter the device name or IP address followed by a colon ":". All interfaces with IP addresses on the device are displayed. | ||
Step 5 | (Optional)To configure source and destination ports or protocols, click More Options. | ||
Step 6 | (Optional)In the Source Port field, enter the port number of the host where you want the trace to end. | ||
Step 7 | (Optional)In the Destination Port field, enter the port number of the host where you want the trace to end. | ||
Step 8 | (Optional)In the Protocol field, choose either tcp or udp from the drop-down menu for the Layer 4 path trace protocol. | ||
Step 9 | (Optional)To configure the path trace to refresh every 30 seconds, check the Periodic Refresh (30 sec) check box. | ||
Step 10 | Check the Stats check box. | ||
Step 11 | Check one or both of the following check boxes:
| ||
Step 12 | Click Start Trace.
The results are displayed in the Trace Results Device Details pane. For information, see Understanding the Interface Statistics Retrieved During a Path Trace and Understanding the QoS Statistics Retrieved During a Path Trace. | ||
Step 13 | (Optional)To view the path trace in the
Topology window. Click View in
Topology.
The Topology window opens with the path trace highlighted in your network.
For more information about the Topology window, see About Topology. |
What to Do Next
Review the path trace output. For information, see Understanding the Interface Statistics Retrieved During a Path Trace and Understanding the QoS Statistics Retrieved During a Path Trace.