Auto-negotiation is recommended when configuring the TippingPoint TPS devices and their link partners. When a TippingPoint TPS port is configured to auto-negotiate the 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 a consistent link between an TPS 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 TPS 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 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 TPS.

When auto-negotiation and software Auto-MDI are disabled, the proper cabling, straight or crossover, depends on the link partner. TPS ports default to DCE (MDI-X), like a switch port. If auto-negotiation and Auto-MDI were disabled, a crossover cable would be necessary to connect a TPS device to a switch. Alternatively, a CLI command is available that can change the default MDI. This command affects all ports on the device.

Note: One important thing to remember when implementing 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, the link will come up, but one or both partners will have RX errors.  The negotiation process will not be completed properly, causing the link partner with Auto-negotiate to be enabled to set itself at half duplex.