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Auto-Negotiation and Auto-MDI

    • Updated:
    • 21 Aug 2017
    • Product/Version:
    • TippingPoint IPS N-series All
    • TippingPoint IPS NX-series All
    • TippingPoint IPS S-series All
    • TippingPoint TPS All
    • Platform:
This article discusses how TippingPoint products manage Auto-Negotiation and Auto-MDI.

Auto-negotiation is the recommended way to configure the TippingPoint IPS devices and their link partners. When a TippingPoint IPS port is configured to auto-negotiate link, the Ethernet port will automatically detect the Medium Dependent Interface (MDI) setting needed to link with its link partner. This is the best, most reliable way to achieve consistent link between an IPS and its link partner. When auto-negotiation is enabled, hardware Auto-MDI is always enabled and cannot be disabled.

When auto-negotiation is disabled, the IPS supports a "software Auto-MDI" method. This method will toggle MDI polarity at a specified interval in an attempt to link up. This software Auto-MDI mode can occasionally create link problems with some link partners. When customers have link problems, and they do not use auto-negotiation, we recommend disabling the software Auto-MDI functionality via the CLI. When Auto-MDI is disabled, this affects all ports on the IPS.

When auto-negotiation and software Auto-MDI are disabled, it is necessary to use the proper cabling, straight or crossover, depending on the link partner. IPS ports default to DCE (MDI-X), like a switch port. To connect an IPS to a switch, it would be necessary to use a crossover cable if auto-negotiation and Auto-MDI where disabled. Alternatively, there is a CLI command available that can change the default MDI. This command affects all ports on the device.

Note: One important thing to remember with Ethernet port configuration is that both link partners must be configured with identical negotiation modes. If one device is configured to auto-negotiate, the other device must also be configured to auto-negotiate. If only one device is configured to auto-negotiate, link will come up, but one or both partners will have RX errors. The negotiation process will not complete properly causing the link partner with Auto-negotiate enabled to set itself at half duplex.

Configure; Troubleshoot; Deploy
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