Brocade MLX Series and Brocade NetIron XMR Diagnostic Guide ...

Layer 1 DiagnosticsChapter3This chapter describes common Layer 1 diagnostic procedures for the Brocade NetIron XMR andBrocade MLX series routers. In general, Layer 1 issues are related to hardware, the most commonbeing the following physical connectivity problems:• Faulty ports• Faulty cables• Faulty hardware• Input and output errors• Cyclic redundancy check (CRC) errors• Excessive or late collisions• Overruns• Output buffer failuresEthernet diagnosticsThe following sections describe how to troubleshoot Layer 1 issues for Ethernet interfaces.Ethernet autonegotiation10BASE-T, 100BASE-TX, and 1000BASE-T all use an RJ-45 connector, which creates the potentialfor connecting electrically-incompatible components to each other, and which can cause networkdisruption. The IEEE developed autonegotiation to eliminate the possibility of dissimilartechnologies interfering with one other.Autonegotiation uses electrical pulses generated by a device over a 10 Mbps, 100 Mbps, or 1000Mbps link (when the link is not sending or receiving data) to detect the presence of a connection toanother device. These unipolar, positive-only pulses have a duration of 100 ns, and are generatedin trains of a maximum of 33 pulses. These pulse trains are referred to as fast link pulse (FLP)bursts. The time interval between the start of each burst is 16 ms, with a tolerance of 8 ms.Autonegotiation and 10BASE-TAn FLP burst is not recognized as valid by a 10BASE-T device receiving it from an autonegotiationdevice. The 10BASE-T device will detect a failure of the link. To avoid this, when the autonegotiationdevice receives the 10BASE-T pulses, it automatically switches to 10BASE-T half-duplex mode. Ifthe 10BASE-T device is operating in full-duplex mode, a duplex mismatch can occur.Brocade MLX Series and Brocade NetIron XMR Diagnostic Guide 5753-1002426-02