Chapter 4 Troubleshooting

Diagnosing Problems

port. Use the show interfaces privileged EXEC command to check the port or interface error-disabled, disabled, or shutdown status on both sides of the connection. If needed, re-enable the port or the interface.

Ping End Device

Check the end device by pinging from the directly connected switch first, and then work your way back port by port, interface by interface, trunk by trunk, until you find the source of the connectivity issue. Make sure that each switch can see the end device MAC address in its Content-Addressable Memory (CAM) table.

Spanning Tree Loops

Spanning Tree Protocol (STP) loops can cause serious performance issues that look like port or interface problems. In this situation, the switch bandwidth is used over and over again by the same frames, leaving little room for legitimate traffic.

Loops can be caused by a unidirectional link. A unidirectional link occurs whenever the traffic sent by the switch is received by its neighbor, but the traffic from the neighbor is not received by the switch. A broken fiber-optic cable, other cabling, or a port issue could cause this one-way communication.

You can enable UniDirectional Link Detection (UDLD) on the switch to help identify difficult-to-find unidirectional link problems. UDLD supports two modes of operation: normal (the default) and aggressive. In normal mode, UDLD detects unidirectional links due to misconnected interfaces on fiber-optic connections. In aggressive mode, UDLD also detects unidirectional links due to one-way traffic on fiber-optic and twisted-pair links and due to misconnected interfaces on fiber-optic links. For information about enabling UDLD on the switch, see the “Understanding UDLD” section in the software configuration guide for this release.

Check Switch Performance

Review this section when troubleshooting switch performance problems.

Speed, Duplex, and Autonegotiation

If the port statistics show a large amount of alignment errors, frame check sequence (FCS), or late-collisions errors, this might indicate a speed or duplex mismatch.

A common issue with speed and duplex is when the duplex settings are mismatched between two switches, between a switch and a router, or between the switch and a workstation or server. This can happen when manually setting the speed and duplex, or from autonegotiation issues between the two devices. 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.

Catalyst 3750-E and Catalyst 3560-E Switch Hardware Installation Guide

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Cisco Systems 3560-E Check Switch Performance, Ping End Device, Spanning Tree Loops, Speed, Duplex, and Autonegotiation
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3750-E, 3560-E specifications

Cisco Systems RPS (Redundant Power System) 2300, along with the 3750-E and 3560-E series switches, represents a significant technological advancement in enterprise networking. These devices are designed to enhance network reliability, scalability, and efficiency, making them integral components in modern enterprise infrastructures.

The Cisco RPS 2300 is designed to provide redundant power to specified Cisco switches, ensuring continuous operation during power disruptions. This system can support up to six devices, enhancing power reliability and reducing downtime. The modularity of the RPS 2300 contributes to its flexibility, allowing enterprises to customize their power solutions to suit their networking needs. It features dual power input, which provides an additional layer of failover capability, ensuring that even in the event of a primary power failure, the backup power system can take over seamlessly.

On the other hand, the Cisco 3750-E series switches are enterprise-class devices that offer a rich feature set to support advanced network functions. These switches come with Cisco’s StackWise technology, enabling users to stack up to nine switches in a single logical unit. This increases port density and simplifies network management. The 3750-E also supports Power over Ethernet (PoE), allowing the delivery of power directly to devices like IP phones and access points through the networking cables. The switch is equipped with high-performance Layer 3 routing capabilities, providing enhanced IP routing options for enterprise networks.

The Cisco 3560-E series switches share many of the advanced features found in the 3750-E models but focus more on providing comprehensive Layer 2 and Layer 3 capabilities in a compact design. The 3560-E series supports Cisco’s advanced security features, such as dynamic VLAN assignment and security group access control lists (ACLs). Additionally, these switches support IPv6, preparing enterprise networks for future growth and addressing requirements.

Both the 3750-E and 3560-E are equipped with energy-efficient technologies, including intelligent power management and support for Energy Efficient Ethernet (EEE), helping organizations reduce their environmental footprint and operating costs. The integration of Cisco’s robust IOS software ensures that these devices are equipped with the latest features, ensuring strong performance, security, and scalability.

In summary, Cisco's RPS 2300, 3750-E, and 3560-E series exemplify the company's commitment to delivering cutting-edge networking solutions that meet the demands of modern enterprises, focusing on reliability, advanced features, and energy efficiency.
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