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Server+ Certification Cram Notes

Network connectivity

Network connectivity issue refers to a problem in establishing or maintaining communication between two or more devices over a network. It can occur due to various reasons, such as hardware or software failures, misconfigurations, security issues, or network congestion. A network connectivity issue can lead to slow or intermittent connections, complete network outage, or failure to access resources or services. Troubleshooting network connectivity issues involves identifying the root cause, testing connectivity between devices, and verifying network settings and configurations. It may require using network diagnostic tools, analyzing network traffic, and checking hardware components like cables, routers, switches, or network interface cards (NICs).

1. Common network connectivity problems

Lack of Internet connectivity: Inability to access the Internet from the network, which can be caused by various issues.

Resource unavailable: Inability to access a network resource, such as a printer, server, or shared folder.

Receiving incorrect DHCP information: Inability to obtain the correct IP configuration from the DHCP server.

Non-functional or unreachable: Inability to access a host or device due to network connectivity issues.

Destination host unreachable: A message indicating that the destination host is not available on the network.

Unknown host: Occurs when a hostname or FQDN cannot be resolved to an IP address.

Unable to reach remote subnets: Occurs when the network is unable to access a remote network or subnet.

Failure of service provider: Inability to access a remote network or the Internet due to service provider issues.

Cannot reach server by hostname/FQDN: Inability to access a server or host by its name.

2. Causes of network connectivity common problems:

Improper IP configuration: Incorrect IP configuration on a host, router, or switch.

IPv4 vs. IPv6 misconfigurations: Incorrect configuration of IPv4 or IPv6 addresses or protocols.

Improper VLAN configuration: Incorrect VLAN configuration, which can prevent hosts from communicating with each other.

Network port security: Improper configuration of port security on a switch, which can prevent unauthorized devices from connecting to the network.

Component failure: Failure of a network component, such as a router, switch, or NIC.

Incorrect OS route tables: Incorrect configuration of route tables on a host.

Bad cables: Faulty or damaged network cables can cause connectivity issues.

Firewall (misconfiguration, hardware failure, software failure): Incorrect firewall configuration or hardware/software failure can prevent access to network resources.

Misconfigured NIC: Incorrect configuration of a network interface card can prevent connectivity.

DNS and/or DHCP failure: DNS or DHCP servers can cause connectivity issues if they are misconfigured or fail.

DHCP server misconfigured: Incorrect DHCP server configuration can prevent hosts from obtaining the correct IP configuration.

Misconfigured hosts file: Incorrect configuration of the hosts file can prevent access to network resources.

Tools and techniques

Check link lights: This tool helps to determine if a network device is properly connected to the network by checking if the link lights on the device are illuminated. If the link light is off, it indicates that there is a problem with the connection.

Confirm power supply: This involves verifying that the network device has a functioning power supply. If the device does not have power, it will not be able to connect to the network.

Verify cable integrity: This involves checking the physical condition of network cables to ensure that they are not damaged, cut or broken. Faulty cables can cause connectivity issues.

Check appropriate cable selection: This involves ensuring that the right type of cable is used for the network connection. For example, a crossover cable is required for a direct connection between two devices, while a straight-through cable is used to connect a device to a network switch.

Commands: The following commands are commonly used to troubleshoot network connectivity issues:

  • ipconfig/ip addr: These commands are used to display the IP address configuration of the network device.

  • ping: This command is used to test the reachability of a network device by sending a packet to the device and waiting for a response.

  • tracert/traceroute: These commands are used to trace the path that a packet takes from the source device to the destination device.

  • nslookup: This command is used to query the Domain Name System (DNS) to obtain information about a specific domain name or IP address.

  • netstat: This command is used to display the network connections, routing tables, and network interface statistics of the device.

  • dig: This command is similar to nslookup and is used to query DNS servers.

  • telnet: This command is used to test the connectivity to a specific port on a remote device.

  • nc: This command is similar to telnet and is used to test the connectivity to a specific port on a remote device.

  • nbtstat: This command is used to display the NetBIOS over TCP/IP (NBT) information for a device.

  • route: This command is used to display the IP routing table of the device.

Command syntax for the above mentioned commands on Linux systems:

1. ipconfig - This command is not available on Linux systems, instead use the following commands:

ifconfig - displays the network interface configuration

ip - similar to ifconfig, but with more options and features

2. ip addr - displays IP address information for all network interfaces Syntax: $ ip addr

3. ping - tests connectivity to a remote host using ICMP packets Syntax:$ ping <host/IP address>

4. traceroute/tracert - traces the route that packets take from the local host to a remote host Syntax: $ traceroute <host/IP address>

5. nslookup - performs DNS lookup and displays information about a domain name or IP address Syntax:

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$ nslookup <domain/IP address>

6. netstat - displays network statistics and connections Syntax: $ netstat [options]

7. dig - similar to nslookup, but with more options and features Syntax:$ dig <domain name>

8. telnet - tests connectivity to a remote host using the Telnet protocol Syntax: $ telnet <host/IP address> <port>

9. nc - similar to telnet, but with more features Syntax: $ nc <host/IP address> <port>

10. nbtstat - displays NetBIOS over TCP/IP (NBT) protocol statistics and connections Syntax: $ nbtstat [options]

11. route - displays and modifies the IP routing table Syntax: $ route [options]


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