# Speed and duplex settings for Security Engines

Mismatched speed and duplex settings are a frequent source of networking problems.

The basic principle for speed and duplex settings is that network cards at both ends of each cable must have identical settings. This principle also applies to the automatic negotiation setting: if one end of the cable is set to auto-negotiate, the other end must also be set to auto-negotiate and not to any fixed setting. Gigabit standards require interfaces to use auto-negotiation. Fixed settings are not allowed at Gigabit speeds.

For Inline Interfaces, the settings must be identical on both links within each Inline Interface pair. Use identical settings on all four interfaces, instead of just matching settings at both ends of each cable (two + two interfaces). If one of the links has a lower maximum speed than the other link, the higher-speed link must be set to use the lower speed.