N10-009 Questions and Answers
Question # 1
A network administrator needs to assign IP addresses to a newly installed network. They choose 192.168.1.0/24 as their network address and need to create three subnets with 30 hosts on each subnet. Which of the following is a valid subnet mask that will meet the requirements?
A.
255.255.255.128
B.
255.255.255.192
C.
255.255.255.224
D.
255.255.255.240
Answer:
C
Explanation:
Understanding the Requirements
Network Address: 192.168.1.0/24
The /24 notation means a subnet mask of 255.255.255.0, providing 256 total addresses (192.168.1.0–192.168.1.255).
Usable hosts: 256 – 2 (network and broadcast) = 254.
Goal: Create 3 subnets, each with 30 hosts.
Each subnet needs enough addresses to accommodate 30 hosts, plus 2 reserved addresses (network and broadcast) per subnet.
Total addresses per subnet = 30 (hosts) + 2 (network/broadcast) = 32 addresses.
Subnetting Basics (Networking Fundamentals)
Subnet Mask: Determines how many bits are borrowed from the host portion to create subnets.
Original Mask: /24 (255.255.255.0) = 24 network bits, 8 host bits.
Formulae:
Number of subnets = 2^(number of borrowed bits).
Number of addresses per subnet = 2^(remaining host bits).
Usable hosts per subnet = 2^(remaining host bits) – 2.
We need:
At least 3 subnets.
At least 32 addresses per subnet (to fit 30 hosts + 2 reserved).
Step-by-Step Analysis
Determine Addresses Needed per Subnet:
32 addresses is a power of 2 (2^5 = 32).
This means each subnet requires 5 host bits (since 2^5 = 32 total addresses, and 32 – 2 = 30 usable hosts).
Calculate Remaining Bits:
Original network has 8 host bits (/24).
If 5 bits are left for hosts, we borrow: 8 – 5 = 3 bits for subnetting.
New Subnet Mask:
Original mask: /24 (24 network bits).
Borrow 3 bits: 24 + 3 = /27.
/27 = 255.255.255.224 (binary: 11111111.11111111.11111111.11100000).
Verify Requirements:
Number of Subnets: 2^3 = 8 subnets (meets the requirement of at least 3).
Addresses per Subnet: 2^5 = 32 addresses.
Usable Hosts per Subnet: 32 – 2 = 30 hosts (exactly meets the requirement).
Subnet Breakdown:
Increment: 256 – 224 = 32 (each subnet increments by 32 in the fourth octet).
Subnets:
192.168.1.0–192.168.1.31 (Network: .0, Broadcast: .31, Hosts: .1–.30)
192.168.1.32–192.168.1.63 (Network: .32, Broadcast: .63, Hosts: .33–.62)
192.168.1.64–192.168.1.95 (Network: .64, Broadcast: .95, Hosts: .65–.94)
(And 5 more subnets up to 192.168.1.255.)
Three subnets fit perfectly with 30 hosts each.
Evaluating the Options
A. 255.255.255.128 (/25):
Borrow 1 bit: 24 + 1 = /25.
Subnets: 2^1 = 2 (not enough, need 3).
Host bits: 7 (2^7 = 128 addresses, 126 hosts).
Why Not: Only 2 subnets, fails the requirement.
B. 255.255.255.192 (/26):
Borrow 2 bits: 24 + 2 = /26.
Subnets: 2^2 = 4 (meets 3).
Host bits: 6 (2^6 = 64 addresses, 62 hosts).
Why Not: 62 hosts exceeds 30, but it’s overkill; /27 is more efficient and still valid.
C. 255.255.255.224 (/27):
Borrow 3 bits: 24 + 3 = /27.
Subnets: 2^3 = 8 (meets 3).
Host bits: 5 (2^5 = 32 addresses, 30 hosts).
Why Yes: Perfectly fits 3 subnets with exactly 30 hosts each.
D. 255.255.255.240 (/28):
Borrow 4 bits: 24 + 4 = /28.
Subnets: 2^4 = 16 (meets 3).
Host bits: 4 (2^4 = 16 addresses, 14 hosts).
Why Not: Only 14 hosts per subnet, fails the 30-host requirement.
Why /27 (255.255.255.224) is Best
It provides exactly 30 usable hosts per subnet, avoiding waste while meeting the minimum requirement.
It allows 8 subnets, exceeding the need for 3, ensuring flexibility.
The study guide emphasizes efficient subnet design, and /27 balances host count and subnet availability.
CompTIA Network+ Context
Networking Fundamentals: Subnetting is a core skill, requiring understanding of CIDR, binary conversion, and address allocation.
Example from Study Guide: Similar problems calculate subnet masks for specific host counts, reinforcing /27 as a common solution for ~30 hosts.
Question # 2
Users are unable to access files on their department share located on file server 2.
The network administrator has been tasked with validating routing between networks
hosting workstation A and file server 2.
INSTRUCTIONS
Click on each router to review output, identify any issues, and configure the appropriate solution.
If at any time you would like to bring back the initial state of the simulation, please click the Reset All button.
Answer:
Answer:
See the solution in Explanation.
Explanation:
To validate routing between networks hosting Workstation A and File Server 2, follow these steps:
Review Routing Tables:
Check the routing tables of Router A, Router B, and Router C to identify any missing routes.
Identify Missing Routes:
Ensure that each router has routes to the networks on which Workstation A and File Server 2 are located.
Add Static Routes:
If a route is missing, add a static route to the relevant destination network via the correct interface.
Routing Table:
Gateway of last resort is 0.0.0.0 to network 0.0.0.0
S* 0.0.0.0/0 is directly connected, GigabitEthernet3
10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
C 10.0.4.0/22 is directly connected, GigabitEthernet2
C 10.0.6.0/24 is directly connected, GigabitEthernet2
L 10.0.6.1/32 is directly connected, GigabitEthernet2
172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C 172.16.27.0/30 is directly connected, GigabitEthernet3
L 172.16.27.1/32 is directly connected, GigabitEthernet3
Routing Table:
Gateway of last resort is 0.0.0.0 to network 0.0.0.0
S* 0.0.0.0/0 is directly connected, GigabitEthernet1
10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
C 10.0.0.0/22 is directly connected, GigabitEthernet1
L 10.0.0.1/32 is directly connected, GigabitEthernet1
172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C 172.16.27.4/30 is directly connected, GigabitEthernet1
L 172.16.27.5/32 is directly connected, GigabitEthernet1
Routing Table:
10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
S 10.0.0.0/22 [1/0] via GigabitEthernet1
S 10.0.4.0/22 [1/0] via GigabitEthernet2
172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C 172.16.27.0/30 is directly connected, GigabitEthernet2
L 172.16.27.2/32 is directly connected, GigabitEthernet2
C 172.16.27.4/30 is directly connected, GigabitEthernet1
L 172.16.27.6/32 is directly connected, GigabitEthernet1
Install Static Route to 10.0.0.0/22 via 172.16.27.1 (assuming Router C's IP is 172.16.27.1):
Destination Prefix: 10.0.0.0
Destination Prefix Mask: 255.255.252.0
Interface: GigabitEthernet3
Install Static Route to 10.0.4.0/22 via 172.16.27.5 (assuming Router C's IP is 172.16.27.5):
Destination Prefix: 10.0.4.0
Destination Prefix Mask: 255.255.252.0
Interface: GigabitEthernet1
Install Static Route to 10.0.6.0/24 via 172.16.27.2 (assuming Router A's IP is 172.16.27.2):
Destination Prefix: 10.0.6.0
Destination Prefix Mask: 255.255.255.0
Interface: GigabitEthernet2
Install Static Route to 10.0.0.0/22 via 172.16.27.1 (assuming Router B's IP is 172.16.27.1):
Destination Prefix: 10.0.0.0
Destination Prefix Mask: 255.255.252.0
Interface: GigabitEthernet1
Summary of Static Routes:
Router A:
ip route 10.0.0.0 255.255.252.0 GigabitEthernet3
Router B:
ip route 10.0.4.0 255.255.252.0 GigabitEthernet1
Router C:
ip route 10.0.6.0 255.255.255.0 GigabitEthernet2
ip route 10.0.0.0 255.255.252.0 GigabitEthernet1
These configurations ensure that each router knows the correct paths to reach Workstation A and File Server 2, resolving the connectivity issue.
Question # 3
Which of the following routing protocols needs to have an autonomous system set in order to establish communication with neighbor devices?
A.
OSPF
B.
EIGRP
C.
FHRP
D.
RIP
Answer:
B
Explanation:
EIGRP (Enhanced Interior Gateway Routing Protocol) is a Cisco proprietary advanced distance-vector routing protocol. While it operates within an Autonomous System (AS), it requires the AS number to be configured for routers to recognize each other as EIGRP neighbors.
OSPF (Open Shortest Path First) uses areas and routers must be in the same area to form adjacencies, but it doesn't require AS numbers in the same way.
FHRP (First Hop Redundancy Protocol) is not a routing protocol but a group of protocols (e.g., HSRP, VRRP) to ensure high availability at the default gateway level.
RIP (Routing Information Protocol) does not use autonomous system numbers.
📘 Reference:
CompTIA Network+ N10-009 Official Objectives: 3.1 – Compare and contrast various routing technologies.
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