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Large Number of Bit Errors Were Caused by Incorrect Duplex Modes

Publication Date:  2015-07-03 Views:  544 Downloads:  0
Issue Description
Network Topology:

As shown in Figure 4-5, the USG serves as the egress gateway of the enterprise to provide Internet access for users on the enterprise intranet.

Figure 4-4 Bit errors caused by incorrect duplex modes


The egress gateway of the enterprise was from another vendor and provided normal Internet access for the enterprise. After the gateway was replaced by the USG, the Internet access speed was slowed down and the web pages could not be displayed sometimes.
Handling Process
1. The WAN interface configuration of the USG was displayed and the speed of the interface was only 100M, and the duplex mode was negotiation, just as expected. After the statistics information about the interface was displayed using the display interface command, the command output indicated that the negotiated duplex mode of the interface was half-duplex and a large number of bit errors occurred. After the duplex mode of the interface was manually set to full-duplex, the number of bit errors was still increasing.

2. A local loopback test was performed, and everything was normal. No packet loss or bit error occurred. Therefore, the fault was not caused by the USG.

3. The speed and duplex mode of the interface was manually changed multiple times, but the negotiation result was always 100M/FULL when the speed and duplex modes were auto-negotiated. After the statistics were cleared using the reset counters interface command and then displayed again, no bit error occurred and the Internet access was resumed.
Root Cause
When the USG is connected to a third-party device, the speed and duplex mode of the USG must match those on the third-party device to avoid packet loss. 
When the USG is connected to a third-party device and the speed and duplex mode are auto-negotiated, the autonegotiation may fail. If the autonegotiation fails, adjust the speed and duplex mode settings. If the fault persists after several adjustment attempts, connect a third-party device for link negotiation.