5.5 troubleshoot general networking issues. Flashcards
Device configuration review
A device configuration review involves examining the settings and parameters of network devices such as routers, switches, firewalls, and access points. This process ensures that the devices are correctly configured according to organizational policies, security best practices, and compliance requirements. Regular reviews help identify any misconfigurations, vulnerabilities, or unauthorized changes that could lead to security incidents or performance issues.
For the exam, it’s crucial to know the key elements to review during a configuration assessment, including firmware versions, access control lists, security settings, and interface configurations. Understanding the significance of documenting changes and maintaining an inventory of device configurations is also essential. Additionally, familiarity with tools and techniques used for conducting these reviews, such as configuration management software and command-line interface commands, will be beneficial in practical scenarios.
- Routing tables
Routing tables are essential data structures used by routers to determine the best path for forwarding packets across a network. They contain a list of routes, which include destination addresses, the next hop, and the associated metrics or costs for reaching those destinations. The routing table enables the router to make informed decisions on where to send data packets, ensuring efficient and effective communication within and between networks.
For the exam, it’s important to understand the components of a routing table, including destination IP addresses, subnet masks, next-hop addresses, and administrative distances. Familiarity with how routing tables are populated, whether through static routes, dynamic routing protocols, or default routes, is also crucial. Additionally, being able to interpret routing table entries and recognize the impact of route metrics on path selection will be beneficial for troubleshooting and optimizing network performance.
- Interface status
Interface status refers to the operational state of a network interface on a device such as a router or switch. It indicates whether the interface is up and functioning properly or down due to issues like a cable disconnect, misconfiguration, or hardware failure. Monitoring interface status is crucial for network management, as it helps in diagnosing connectivity problems and ensuring that network paths are available for data transmission.
For the exam, you should know how to check the status of network interfaces using commands like show interfaces on Cisco devices, which provides detailed information about each interface, including whether it is up or down, its speed, and any errors. Understanding common interface statuses, such as “up/up,” “up/down,” “administratively down,” and what they signify, will aid in troubleshooting network issues effectively. Familiarity with the implications of an interface being down and the steps to rectify such situations is also important.
- VLAN assignment
VLAN assignment refers to the process of grouping devices on a network into separate virtual local area networks (VLANs) to improve network efficiency, security, and management. By assigning devices to different VLANs, network administrators can segment traffic, control broadcast domains, and enhance overall network performance. Each VLAN is identified by a unique VLAN ID, allowing switches to manage traffic appropriately and isolate data traffic between different VLANs.
For the exam, you should understand the significance of VLAN assignment in network design, including how it helps in reducing congestion and improving security by limiting access between different network segments. Familiarity with configuring VLANs on switches, including commands like switchport access vlan for port assignment and how to verify VLAN configurations, is essential. You may also need to know about VLAN tagging protocols such as IEEE 802.1Q, which are used to identify VLANs in tagged frames, as well as concepts related to trunking, which allows multiple VLANs to traverse a single link between switches.
- Network performance baselines
Network performance baselines refer to the standard measurements of network performance metrics over time, establishing a reference point for evaluating network behavior under normal operating conditions. These metrics typically include bandwidth usage, latency, packet loss, jitter, and error rates. By collecting this data, network administrators can identify performance trends, detect anomalies, and assess the impact of changes or upgrades made to the network.
For the exam, it’s important to understand the purpose of establishing baselines, as they provide a crucial benchmark for troubleshooting network issues and optimizing performance. You should be familiar with methods for collecting baseline data, such as network monitoring tools and performance testing techniques. Additionally, knowing how to analyze the data to make informed decisions about network capacity planning and identifying deviations from expected performance can be vital for effective network management.
Collisions
Collisions in networking occur when two or more devices attempt to send data over a shared communication medium at the same time, resulting in data packets interfering with each other. This is particularly relevant in traditional Ethernet networks using a hub, where devices share the same bandwidth. When a collision happens, the affected devices must detect it and retransmit their data after a random backoff period, which can lead to delays and decreased network performance.
For the exam, you should know the impact of collisions on network efficiency and how they are managed. Familiarity with protocols such as Carrier Sense Multiple Access with Collision Detection (CSMA/CD) is important, as it explains how devices listen to the network before transmitting to avoid collisions. Additionally, understand that in switched networks, collisions are greatly reduced because each device has a dedicated bandwidth, making collisions less common in modern network designs.
- Broadcast storm
A broadcast storm occurs in a network when a large number of broadcast packets are transmitted simultaneously, overwhelming the network’s capacity. This situation typically arises in Ethernet networks when devices send broadcast messages to all nodes, and those nodes, in turn, send their own broadcasts in response. As the number of broadcasts increases, it can consume substantial bandwidth and processing resources, leading to network congestion, latency, and potential service disruption.
For the exam, you should understand the causes and effects of broadcast storms. Familiarity with network topologies and protocols that can mitigate broadcast storms, such as Spanning Tree Protocol (STP), is also essential. STP helps prevent loops in a network that can lead to broadcast storms by managing how switches communicate with each other. Recognizing the importance of segmenting networks to control broadcast traffic can be crucial for maintaining network performance and reliability.
- Duplicate MAC address
A duplicate MAC address occurs when two or more devices on the same network share the same Media Access Control (MAC) address. MAC addresses are unique identifiers assigned to network interfaces for communications on the physical network segment. When duplicates exist, it can cause network connectivity issues, as network switches may not be able to properly direct traffic to the correct device. This situation often leads to data packets being sent to the wrong device, resulting in dropped connections and disrupted services.
For the exam, it’s important to know how duplicate MAC addresses can affect network performance and connectivity. Understanding how to identify and resolve duplicate MAC addresses is essential. Familiarity with tools like ARP (Address Resolution Protocol) can help diagnose these issues, as ARP can show the mapping of IP addresses to MAC addresses on the network. You may also need to recognize common scenarios that lead to duplicate MAC addresses, such as misconfigured virtual machines or improperly restored devices.
- Duplicate IP address
A duplicate IP address occurs when two devices on the same network are assigned the same Internet Protocol (IP) address. This situation can create significant connectivity problems, as IP addresses are used to uniquely identify devices on a network. When a duplicate IP exists, it can cause network conflicts, resulting in both devices experiencing intermittent connectivity or being unable to communicate with other devices on the network.
For the exam, it’s important to understand the implications of duplicate IP addresses and how they can disrupt network services. You should know how to diagnose this issue using tools such as the ARP table or ping commands. Being aware of common causes of duplicate IP addresses, such as static IP assignment conflicts or DHCP server misconfigurations, is also crucial. Additionally, understanding methods to resolve this issue, including reassigning IP addresses or updating DHCP settings, can be helpful in troubleshooting scenarios.
- Multicast flooding
Multicast flooding occurs when multicast traffic is sent to all devices on a network segment, rather than being delivered to a specific group of devices that have subscribed to that multicast stream. This situation typically arises when multicast traffic is not properly managed, leading to unnecessary load on network resources. In an efficient multicast setup, routers and switches should intelligently direct multicast packets only to the devices that need them, thus conserving bandwidth.
For the exam, it’s essential to know how multicast works and the protocols involved, such as Internet Group Management Protocol (IGMP) and Protocol Independent Multicast (PIM). Understanding how switches use IGMP snooping to limit multicast flooding by monitoring which devices are interested in which multicast groups is also crucial. Be prepared to identify symptoms of multicast flooding, such as excessive network traffic or degraded performance, and know how to mitigate it through proper network configuration and monitoring practices.
- Asymmetrical routing
Asymmetrical routing occurs when data packets take different paths to and from a destination, resulting in unequal routing paths. This situation can arise from the use of multiple routes in a network, particularly when dynamic routing protocols are involved. Asymmetrical routing can lead to issues such as increased latency, dropped packets, or problems with stateful devices like firewalls, which may not track sessions correctly if traffic comes from different paths.
For the exam, it’s important to recognize the potential complications caused by asymmetrical routing, especially in relation to network performance and security. You should understand how routing protocols handle paths and how to diagnose issues related to asymmetrical routing. Knowledge of tools like traceroute can help you identify routing paths and determine if asymmetry is causing network problems. Familiarity with solutions, such as ensuring symmetric routes through configuration adjustments or network design considerations, can also be beneficial.
- Switching loops
Switching loops occur when there are multiple paths between switches in a network, causing data packets to circulate indefinitely. This can lead to broadcast storms, excessive network traffic, and potential network outages, as switches continuously forward packets back and forth. Switching loops typically arise in networks with redundant paths designed for fault tolerance but without proper loop prevention mechanisms in place.
For the exam, it’s crucial to understand the impact of switching loops on network performance and stability. Familiarity with protocols like Spanning Tree Protocol (STP) is essential, as STP is designed to detect and eliminate loops by blocking redundant paths. Knowing how to configure STP and the role of bridge priorities and port costs can help maintain a loop-free topology. Recognizing symptoms of a switching loop, such as high CPU usage on switches or flooding of broadcast packets, is also important for troubleshooting purposes.
- Routing loops
Routing loops occur when a data packet is continuously passed between routers without reaching its destination, effectively creating a loop in the network’s routing paths. This situation typically arises from incorrect routing table entries or misconfigured routing protocols, leading to packets circulating endlessly between routers. The main consequences of routing loops include increased network latency, excessive bandwidth consumption, and potential network outages.
For the exam, it’s important to know how routing loops can negatively impact network performance and the mechanisms used to prevent them. Familiarity with protocols like Distance Vector Routing Protocols (such as RIP) is crucial, as they are particularly susceptible to routing loops. Concepts like route poisoning, split horizon, and hold-down timers can help mitigate routing loops by ensuring that incorrect routes are not propagated throughout the network. Understanding the symptoms of a routing loop, such as network congestion or inconsistent routing tables, is essential for effective troubleshooting and network management.
- Rogue DHCP server
A rogue DHCP server is an unauthorized device on a network that provides DHCP (Dynamic Host Configuration Protocol) services, distributing IP addresses and network configurations to clients. This can lead to various network issues, such as IP address conflicts, disruption of network services, or exposure to security threats. A rogue DHCP server may be set up intentionally by an attacker to intercept traffic or conduct man-in-the-middle attacks, or it could be a misconfigured device on the network.
For the exam, it’s important to understand the risks associated with rogue DHCP servers and their potential impact on network security. Knowledge of preventive measures, such as enabling DHCP snooping on switches to filter out unauthorized DHCP messages and ensuring that only authorized DHCP servers are allowed to operate on the network, is essential. Recognizing symptoms of a rogue DHCP server, such as unexpected IP address assignments or clients being unable to connect to the network properly, can aid in troubleshooting and maintaining network integrity.
- DHCP scope exhaustion
DHCP scope exhaustion occurs when a DHCP server runs out of available IP addresses to assign to clients within its defined address range, or scope. This typically happens when there are too many devices trying to connect to the network simultaneously, exceeding the number of addresses available in the DHCP scope. When scope exhaustion occurs, new devices will be unable to obtain an IP address, resulting in connectivity issues.
For the exam, it’s crucial to recognize the signs of DHCP scope exhaustion, such as users reporting connectivity problems or devices failing to join the network. Understanding the implications, like the potential for network disruptions and the necessity for proper capacity planning, is important. Solutions include expanding the DHCP scope by increasing the range of available IP addresses, using static IP assignments for critical devices, or implementing DHCP failover to provide redundancy. Awareness of best practices for DHCP management, such as regular monitoring of address utilization, is key to preventing scope exhaustion.
