Faulty or loose cables. Look for loose or obviously faulty connections. If they appear to be OK, make sure the connections are snug. If that does not correct the problem, try a different cable.

Non-standard cables. Non-standard and mis-wired cables may cause network collisions and other network problems, and can seriously impair network performance. Use a new correctly-wired cable, or compare your cable to the cable in “Cabling and Technology Information Specifications” in the HPE 5400R zl2 Switches Installation and Getting Started Guide, for pinouts and correct cable wiring. A category 5 cable tester is a recommended tool for every 100Base-TX and 1000Base-T network installation.

Improper Network Topologies. It is important to make sure you have a valid network topology. Common topology faults include excessive cable length and excessive repeater delays between end nodes. If you have network problems after recent changes to the network, change back to the previous topology. If you no longer experience the problems, the new topology is probably at fault.

In addition, you should make sure that your network topology contains no data path loops. Between any two end nodes, there should be only one active cabling path at any time. Data path loops will cause broadcast storms that will severely impact your network performance.

With your 5400R zl2 switches, if you wish to build redundant paths between important nodes in your network to provide some fault tolerance, you should enable Spanning Tree Protocol support on the switch. This ensures that only one of the redundant paths is active at any time, thus avoiding data path loops. Spanning Tree can be enabled through the switch console, the web browser interface, or IMC.

The 5400R zl2 switches also support trunking, which allows multiple network cables to be used for a single network connection without causing a data path loop. See the Management and Configuration Guide for more information on spanning tree and on trunking at www.hpe.com/networking/support.

Connecting to devices that have a fixed full-duplex configuration. The RJ-45 ports on the 5400R zl2 switches are all configured as “Auto”. That is, when connecting to attached devices, the switch will operate in one of two ways to determine the link speed and the communication mode (half duplex or full duplex):

Because the 5400R zl2 switches behave in this way (in compliance with the IEEE 802.3 standard), if a device connected to the switch has a fixed configuration at full duplex, the device will not connect correctly to the switch. The result will be high error rates and very inefficient communications between the switch and the device.

Ensure that all devices connected to the 5400R zl2 switches are configured to auto negotiate, or are configured to connect at half duplex (all hubs are configured this way, for example).

If necessary though, you can modify the configuration of the ports on the 5400R zl2 switches to match the configuration of the connected device. Use the switch console, the web browser interface, or IMC to modify the port configuration.

Check the port configuration. A port on your 5400r zl2 switch may not be operating as you expect because it has been put into a “blocking” state by Spanning Tree, GVRP (automatic VLANs), or LACP (automatic trunking). (Note that the normal operation of the Spanning Tree, GVRP, and LACP features may put the port in a blocking state.) Or, the port just may have been configured as disabled through software.

Use the switch console to determine the port’s configuration and verify that there is not an improper or undesired configuration of any of the switch features that may be affecting the port. See the Management and Configuration Guide for your switch at www.hpe.com/support/hpesc.