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

Collisions and Broadcast Storms
o 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
o Use a router to break up subnets into separate broadcast
domains
● Large volume of DCHP requests
o Discover
o Offer
o Request
o Acknowledge
● Loops are created in the switching environment
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 9

Duplicate Addresses
o MAC Address

Answer 9

Used to uniquely identify a network interface card on a given network
● D2:51:F1:3A:34:65
o Vendor code: D2:51:F1
o Unique Value: 3A:34:65
▪ MAC addresses are only used in your Layer 2 networks
▪ Logical Domain Manager
▪ Listens to multicast messages on a network and keeps track of the MAC
addresses being used
▪ Enable port security on your switches

Question 10

Duplicate IP Address/ IP Address Conflict

Answer 10

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

Question 11

Routing Issues
o Multicast Floodin

Answer 11

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

Question 12

Asymmetrical Routing

Answer 12

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

Question 13

Missing Routes

Answer 13

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

Question 14

Switching/ Bridge Loop

Answer 14

Switching loops are usually an issue with how STP is configured

Question 15

Routing Loop

Answer 15

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 16

Split Horizon

Answer 16

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 17

Route Poisoning

Answer 17

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

Question 18

Hold-Down Timer

Answer 18

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 19

● DHCP Issues
o Dynamic Host Configuration Protocol (DHCP

Answer 19

Automatically assigns an IP address, subnet mask, default gateway, and
DNS server’s IP address to a client when it joins a network

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
o Occurs when the DHCP server runs out of valid IPs to
assign to the clients requesting access on the network
▪ 192.168.1.0/24
▪ 192.168.1.1
▪ 192.168.1.255
● Default Lease Time
o 1440 seconds (1 day)
o 7 days
o 30 days
● Default Lease Time
o 1440 seconds (1 day)
o 7 days
o 30 days
● Default Lease Time
o 1440 seconds (1 day)
o 7 days
o 30 days

Question 21

IP and VLAN Settings

Answer 21

o 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
▪ IP address
● Occur when you have an incorrect IP address, subnet mask,
gateway, or DNS server IP address assigned to a client
▪ Subnet mask
▪ Default gateway IP
▪ DNS server IP
● Make sure you have a working DNS server and the IP is properly
entered on the client

Question 22

Firewall Issues
o Firewall

Answer 22

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

Question 23

Host-Based Firewall

Answer 23

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

Question 24

Network-Based Firewall

Answer 24

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)
Provides security by blocking unauthorized users and allowing authorized
users to access specific resources

Question 25

DNS and NTP Issues
o DNS

Answer 25

▪ 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
▪ Time to live (TTL) set correctly?

Question 26

DNS Latency

Answer 26

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

Question 27

NTP

Answer 27

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 28

Network Performance Issues

Answer 28

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

Question 29

DNS problems

Answer 29

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 30

Other Issues

Answer 30

Low optical link budgets
▪ 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
o 0.25 dB per km for a standard fiber optic cable
o Calculate optical link budget by using power budget minus
the loss over the fiber cable’s distance

Question 31

Certificate issues

Answer 31

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

Question 32

BYOD challenges

Answer 32

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