Troubleshooting Network Issues

Question 1

Startup Configuration

Answer 1

Stored in NVRAM and contains the commands needed to initially
configure a router

Question 2

Running Configuration

Answer 2

Actively being used by the router at that moment

Question 3

VLAN Assignment/Tagging

Answer 3

▪ Practice of segmenting an IT organization’s network, separating users
into respective network sections
▪ VLAN Membership Policy Server (VMPS), client, server, and database

Question 4

Network Performance Baseline

Answer 4

Defines the normal working conditions of an enterprise network
infrastructure

Question 5

Collision

Answer 5

▪ Occurs when two hosts on the network transmit at the same time which
causes the signals to combine on the network medium
▪ Collisions occur in both wired and wireless networks

Question 6

Collision Domain

Answer 6

▪ Network segment where simultaneous data transmissions collide with
one another
▪ Use any Layer 2 device to break apart collision domains
● Turn off autonegotiation
● Hardcode lower speed
● Change to half-duplex

Question 7

Broadcast Storm

Answer 7

▪ Occurs when a network system is overwhelmed by continuous multicast
or broadcast traffic
● Layer 2
o FF:FF:FF:FF:FF:FF
● Layer 3
o 255.255.255.255

Question 8

Broadcast Domain

Answer 8

▪ A logical division of computer network where all nodes can reach each
other by broadcast at the data link layer
▪ Layer 2 devices will not break up a broadcast domain
● Too large singular broadcast domain
● Large volume of DCHP requests - DORA
● Loops are created in the switching environment

Question 9

Too large singular broadcast domain

Answer 9

Use a router to break up subnets into separate broadcast

domains

Question 10

Loops are created in the switching environment

Answer 10

o Enable Bridge Protocol Data Units (BPDU) on managed
switches
o Enforce a maximum number of MAC addresses per port
o Break up large broadcast domains into smaller domains
using routers and Layer 3 switches

Question 11

Duplicate IP Address/ IP Address Conflict

Answer 11

▪ Occurs when another computer on the same network has an identical IP
to another workstation or server on the same network
● Static IP address issue
● DHCP server issue
● Rogue DHCP server

Question 12

Multicast Flooding

Answer 12

No specific host is associated with the multicast MAC address in the CAM
table of the switch

Question 13

Asymmetrical Routing

Answer 13

▪ Network packets leave via one path and return via a different path
▪ Routing issues cause issues with dropped packet flows

Question 14

Missing Routes

Answer 14

▪ When a router cannot reach a destination because there is a missing
route in the routing table

Question 15

Switching/ Bridge Loop

Answer 15

Switching loops are usually an issue with how STP is configured

Question 16

Routing Loop

Answer 16

▪ Formed when an error occurs in the operation of the routing algorithm
and creates a circular route amongst a group of network devices
▪ Routing loops are caused by logical Layer 3 circular connections that may
exist in a routing table
● Time to Live (TTL)

Question 17

Split Horizon

Answer 17

▪ Routing configuration that stops a route from being advertised back in
the direction from which it came
● ip split-horizon
● no ip split-horizon

Question 18

Route Poisoning

Answer 18

Increasing a router’s metric to an infinitely high number after detecting
one of its connected routes has failed

Question 19

Hold-Down Timer

Answer 19

▪ Prevents bad routes from being restored and passed to other routers by
accident
● Hold-down period
● 180 seconds (3 minutes)
▪ Statically-created routes are given a metric of 1 by default

Question 20

Rogue DHCP Server

Answer 20

▪ A DHCP server on a network which is not under the administrative
control of the network administrators
● DHCP snooping
● Port security
● Intrusion detection
● DHCP Scope Exhaustion

Question 21

DHCP Scope Exhaustion

Answer 21

Occurs when the DHCP server runs out of valid IPs to

assign to the clients requesting access on the network

Question 22

IP and VLAN Settings

Answer 22

Make sure you check your configuration and that there is proper routing setup
between the VLANs, because this is the number one cause of issues when you’re
dealing with VLANs that won’t communicate

Question 23

Firewall

Answer 23

Network security device that monitors and filters incoming and outgoing
network traffic based upon established rule sets

Question 24

Host-Based Firewall

Answer 24

Runs on an individual computer or device connected to the network to
protect that one device

Question 25

Network-Based Firewall

Answer 25

Deployed in line with the network traffic flow to monitor and filter
incoming and outgoing network traffic based on established rule sets
● Access to protected resources from unprotected networks is not
working
● Access to unprotected resources from protected networks is not
working
● Access to the firewall and its configurations is not working
● Access Control List (ACL)

Question 26

DNS

Answer 26

Matches domain names with the corresponding IP addresses used by a
server
● Issue on a single network client or on a larger network?
● Connectivity between client and DNS server?
● A records and CNAME records properly created?
o nslookup

Question 27

DNS Latency

Answer 27

Time and delay that occurs whenever users request a particular domain
name

Question 28

NTP

Answer 28

▪ Allows synchronization of system clocks between different layers of a
hierarchical, semi-layered system of time sources
● Not received
● Not processed
● Errors or packet loss
▪ Ensure network client is operating the NTP service
● Network saturation
● Network connectivity

Question 29

Network Performance Issues

Answer 29

o High CPU usage
o High bandwidth usage
o Poor connectivity
o Network malfunction

Question 30

DNS problems

Answer 30

o High CPU usage increases latency, jitter, and packet loss
o Use a cable tester for twisted pair connections or a fiber light meter for fiber
optic connections

Question 31

Low optical link budgets

Answer 31

Optical Link Budget is a calculation that considers all the anticipated
losses along the length of a fiber optic connection
● Reduced transmission
● Slow connection speeds
● Connection downtime

Question 32

Certificate issues

Answer 32

A digital Certificate is used as a credential to facilitate verification of
identities between users in a transaction

Question 33

BYOD challenges

Answer 33

Bring Your Own Device (BYOD) policies allows a user to bring their own
smartphones, laptops, and other devices to work and use them on the
organization’s network
● Decrease in Capital Expenditures
● Increase in Operational Expenditures