Chapter 4 Troubleshooting

Diagnosing Problems

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

Ping the End Device

Verify the end device connection by first pinging it from the directly connected switch, 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 identify 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 might appear to be port or interface problems. In this situation, the switch bandwidth is used repeatedly by the same frames, crowding out legitimate traffic.

A unidirectional link can cause loops. This occurs when the traffic that the switch sends is received by its neighbor, but the switch does not receive the traffic that is sent from the neighbor. A broken fiber-optic cable, other cabling, or a port issue could cause this one-way communication.

You can enable the UniDirectional Link Detection (UDLD) protocol on the switch to help identify difficult-to-find unidirectional link problems. UDLD supports a normal mode of operation (the default) and an aggressive mode. In normal mode, UDLD detects unidirectional links because of incorrectly connected interfaces on fiber-optic connections. In aggressive mode, UDLD also detects unidirectional links caused by one-way traffic on fiber-optic and twisted-pair links and by incorrectly connected interfaces on fiber-optic links. For information about enabling UDLD on the switch, see the “Understanding UDLD” section in the software configuration guide.

Monitor Switch Performance

Review these sections when you troubleshoot switch performance problems:

Speed, Duplex, and Autonegotiation, page 4-4

Autonegotiation and NIC Cards, page 4-5

Cabling Distance, page 4-5

Speed, Duplex, and Autonegotiation

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

A common issue with speed and duplex occurs 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 you manually set the speed and duplex or because of autonegotiation issues between the two devices.

These circumstances can result in a mismatch:

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.

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Cisco Systems 2960 specifications Monitor Switch Performance, Ping the End Device, Spanning Tree Loops

2960 specifications

Cisco Systems 2960 series switches are a prominent solution in the networking landscape, known for their reliability, scalability, and feature-rich offerings. Ideal for small to medium-sized enterprises, these switches provide a robust foundation for network infrastructure, ensuring optimal performance and connectivity.

One of the standout features of the Cisco 2960 series is its Layer 2 switching capabilities. The switches support multiple VLANs (Virtual Local Area Networks), allowing network administrators to segment traffic efficiently and enhance security protocols. This is crucial in modern networks where managing traffic and isolating sensitive information is a priority.

The Cisco 2960 series also incorporates advanced Quality of Service (QoS) features, enabling the prioritization of critical applications and services. This functionality ensures that time-sensitive data, such as voice and video traffic, maintains a high quality of service even in congested networks. With support for IEEE 802.1p and DSCP marking, administrators can fine-tune their network performance to meet specific organizational needs.

Power over Ethernet (PoE) is another significant characteristic of the Cisco 2960 series. This feature allows switches to deliver electrical power alongside data over Ethernet cables to devices such as IP phones, wireless access points, and surveillance cameras. With PoE, organizations can reduce clutter from power cables and increase deployment flexibility for various devices.

In terms of security, the Cisco 2960 series is equipped with a range of integrated security features. The switch supports port security, 802.1X authentication, and Access Control Lists (ACLs), providing robust defenses against unauthorized access and potential network vulnerabilities. These security measures are essential for protecting sensitive data and ensuring compliance with industry regulations.

Moreover, the Cisco 2960 series offers enhanced network management capabilities with Cisco's Intelligent Network Services. This includes support for Simple Network Management Protocol (SNMP), Cisco Prime, and Embedded Event Manager (EEM), allowing for efficient monitoring, troubleshooting, and policy enforcement across the network.

Additionally, the Cisco 2960 switches provide various models and configurations, catering to different networking needs. Options include models with varying port densities, uplink configurations, and stacking capabilities, making it easy for organizations to choose solutions that align perfectly with their requirements.

In summary, the Cisco 2960 series is a versatile and essential component of modern networking environments. Its advanced features, including Layer 2 support, QoS, PoE, robust security, and diverse management tools, make it an excellent choice for organizations looking to build a strong and secure network infrastructure.