Cisco 2950G 24 Software Configuration Guide - Page 574

Preventing Autonegotiation Mismatches Chapter 28 Troubleshooting Preventing Autonegotiation Mismatches The IEEE 802.3AB autonegotiation protocol manages the switch settings for speed (10 Mbps, 100 Mbps, and 1000 Mbps excluding GBIC ports) and duplex (half or full). There are situations when this protocol can incorrectly align these settings, reducing performance. A mismatch occurs under these circumstances: • A manually-set speed or duplex parameter is different from the manually set speed or duplex parameter on the connected port. • A port is set to autonegotiate, and the connected port is set to full duplex with no autonegotiation. To maximize switch performance and ensure a link, follow one of these guidelines when changing the settings for duplex and speed: • Let both ports autonegotiate both speed and duplex. • Manually set the speed and duplex parameters for the ports on both ends of the connection. Note If a remote device does not autonegotiate, configure the duplex settings on the two ports to match. The speed parameter can adjust itself even if the connected port does not autonegotiate. Troubleshooting LRE Port Configuration Table 28-4 lists problems that you might encounter when configuring and monitoring the Long-Reach Ethernet (LRE) ports on the Catalyst 2950 LRE switches. For additional information about what can affect LRE connections, see the "Environmental Considerations for LRE Links" section on page 7-18. LRE command descriptions provide additional troubleshooting information. Refer to the switch command reference. See the Release Notes for the Catalyst 2950 Desktop Switch, Release 12.1(11)YJ for switch upgrade and CPE device upgrade troubleshooting information. Table 28-4 LRE Port Problems Problem Amber LRE port LED Excessive CRC errors on an LRE link Suspected Cause and Suggested Solution The switch and CPE device are unable to establish an LRE link using the selected profile. • Change to a profile with a lower data rate (for example, use LRE-5 instead of LRE-15). • Reduce the effect of stubs or bridge taps by terminating them with 300-ohm microfilters. • A noisy environment (such as motors and power surges) is causing interference with the LRE link. - Change to a profile that has the interleaver feature enabled, such as the LRE-5, LRE-10, LRE-15, LRE-10-1, LRE-10-3, or LRE-10-5 profile. - Change to a profile with a lower data rate (for example, use LRE-5 instead of LRE-15) to increase the noise margin. • The LRE link length and quality are close to the limit of operation. - Change to a lower profile (for example, LRE-5 instead of LRE-15). - Reduce the effect of stubs or bridge taps by terminating them with 300-ohm microfilters. 28-12 Catalyst 2950 Desktop Switch Software Configuration Guide 78-14982-01