Troubleshoot Switch Port & Interface Problems
[ Map + App ]

When the network is underperforming, or isn't working at all, a layer-2 switch port or interface issue may be to blame. Interface problems can cause disruptions in connectivity or even compromise the security of the network.

NetBrain's 'Map+App' troubleshooting methodology can help you troubleshoot interface problems effectively, through automation. You can instantly create a dynamic network map to target the problem interfaces, then, you can drill down with NetBrain apps to automatically diagnose the connectivity, performance, and configuration of each interface.

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Build a Map

To target problem devices and interfaces

The first step to troubleshooting any network issue is to identify the area of the network that is experiencing or causing problems. A network map is the best visual asset to help you identify and understand the symptomatic interfaces. NetBrain provides several ways to create or open a targeted map on-demand. For example, you can start by mapping the relevant switch group.

Map a Targeted Switch Group Automatically

You can dynamically extend the devices that are viewable on the map by clicking on a device that has a '+' sign (indicating the device has neighbors not currently displayed):

Dynamically Add Devices to Map View

Learn more about dynamic network mapping »

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Run Apps

To analyze application performance & design dependancies

NetBrain apps provides a way for you to collect data from the network without having to log into a bunch of switches serially and type in a string of show commands. NetBrain has several built-in apps that can automate interface diagnoses. Most importantly, you can easily write your own apps to automate much more. These apps run directly from the map and leverage the map as the ‘canvas’ for your targeted data analysis.

Recommended App: Highlight VLAN

Sometimes devices in the same VLAN can't reach one another. One possible cause is that the interfaces aren't assigned to the proper VLAN. To verify that interface assignments were configured properly, you can run the Highlight VLAN app. This will help ensure that both sides of the link are configured properly. This app is also helpful for verifying that the proper VLANs are allowed on each trunk port.

This App Highlights Each Port to Reflect the VLAN

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Recommended App: Overall Health Monitor

From a high-level perspective, it's a good idea to identify if any interfaces are down or flapping (up/down). The Monitor Network Health app will perform a continuous SNMP scan of the network to determine interface status and link performance (delay, errors, and utilization) to alert you to interfaces that have connectivity issues.

This app will continuous monitor and plot the status of each interface as long as it's running. If an interface goes down, or a link gets clogged up, you can be alerted automatically.

Automatically Monitor and Chart Interface Status

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Recommended App: Check Interface Errors

If the link is experiencing degraded performance, it could be due to a physical (layer-1) problem. The most effective way to discover physical layer problems is to look at that output from the show interfaces command (for Cisco switches). There are various errors you may look for which may hint at a bad cable or interface configuration issue:

Runts: Runts are frames smaller than 64bytes

CRC errors: The 'Cyclic redundancy checksum' value does not match the one calculated by the transmitting switch or router

Collisions: Look for collisions on a full-duplex interface or excessive collision on a half-duplex interface.

Frames: Frame errors are usually associated with CRC errors

By running the app Check Interface Errors, you can immediately determine whether these errors exist on any link on the map, and (more importantly) whether or not the errors are increasing.

This App Will Detect Interface Errors and Display Them on the Map

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Recommended App: Detect Speed/Duplex Mismatch

Another common cause of degraded link performance is a duplex mismatch. Duplex mismatches usually won't bring a link down, but they will result in suboptimal performance. You would suspect a duplex mismatch if you saw collisions on a full-duplex link (by running the Check Interface Errors app) because a full-duplex link should never have collisions.

Cisco switches use Ethernet auto-negotiation, by default, to determine the speed and duplex setting, however a duplex mismatch might be caused by hard-coding one side of the link to full duplex but leaving the other side to auto negotiate. To determine if any such hard-coding mistakes have been configured on the network, you can run the Detect Speed/Duplex Mismatch app.

This App Detects Speed or Duplex Mismatches Automatically

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Write Your Own Apps

There could be many other issues affecting interface performance, which the apps above might not detect. With NetBrain's adapative automation, you can write an app yourself to automate any further analysis you can think of.

Writing an app is almost as easy as typing a show-command. There's no complex syntax or steep learning curve - after just 15 minutes of training you’ll be ready to write your first app. There are three main steps:

Step 1:
Define Variables of Interest

A sample of CLI command data is used to identify variables which indicate fields of interest. For example, an interface diagnosis app may use the 'show interface' IOS command to extract the speed and duplex from each interface.

Step 2:
Define Data Positions on the Map

An app uses the map to display the desired device and interface data. The positions of the data on the map are easily defined during app definition.

Step 3 (optional):
Define Alarm Thresholds

To raise an alarm, users can indicate a threshold condition and associated warning message which is raised if a variable exceeds the threshold.

After you write an app, you can run it directly on the map, as if it was built into the software:

Example Custom App Using ‘Show Interface’ IOS Command to Extract Interface Errors

Learn more about NetBrain Apps »

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Solve virtually any network problem with NetBrain's ' Map + App'

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