CCNA 1 v6.0 Chapter 8: Subnetting IP Networks: Check your Understanding Answers
1. What are advantages of subnetting a large network? (Choose two.)
- More address space is created.
- Overall network traffic is reduced.
- IP addresses can be reused on the same subnetwork.
- Network performance is improved.
- Layer 3 devices are not required when a network is subnetted.
Explanation: Subnetting a large address space into smaller subnetworks helps to contain network traffic and thus improve network performance.
2. What would allow devices on different subnets to be able to communicate?
- Layer 2 switch
Explanation: A router or Layer 3 switch is required for devices on different networks or subnets to be able to communicate.
3. Fill in the blank.
To create subnets, bits are borrowed from the ____ portion of an IP address.
host. Subnets are created by borrowing bits from the host portion of an IP address to create additional network bits. The more bits borrowed, the more subnets created.
4. How many subnets can be created if 4 bits are borrowed to specify subnets?
Explanation: Every bit borrowed can have one of two values, 0 or 1. The number of subnets created is 2n, where n is the number of bits borrowed. In this case, we have borrowed 4 bits, so 24, or 16, subnets are created, all of which can be used.
5. What best describes a network broadcast address?
- All 0 bits in the host portion of the address
- All 0 bits plus a rightmost 1 bit in the host portion of the address
- All 1 bits plus a rightmost 0 bit in the host portion of the address
- All 1 bits in the host portion of the address
Explanation: A network broadcast address has all host bits turned on.
6. How many valid host addresses are created when 4 host bits are borrowed from the 10.20.20.0/24 network?
Explanation: The number of valid host addresses created by borrowing 4 bits is 24–2, or 14. It is necessary to subtract 2 because the network address and the broadcast address for each subnet cannot be used as host addresses.
7. A junior network technician has subnetted the 10.20.30.0/24 address space by borrowing 3 bits. The technician decides to use the second subnet for the Accounting department computers. Which of the following addresses could the network technician assign to hosts? (Choose three.)
Explanation: By borrowing 3 bits, the technician created nine subnets, each with 30 usable hosts. The second subnet is 10.20.30.32/27 and consists of addresses from 10.20.30.32 to 10.20.30.63. The first and last addresses in this range are not usable, but all others are.
8. A junior network technician is assigning host addresses to devices in the 192.168.1.0/25 subnet. The departmental printer is assigned the address 192.168.1.131/25 with a 192.168.1.1/25 default gateway. No one in the department is able to print. What is the cause of the problem?
- The default gateway is not correct for the departmental subnet.
- The printer has been assigned a broadcast IP address.
- The printer has been assigned an address on another subnet.
- The printer has been assigned a network IP address.
Explanation: The assigned subnet has the address range from 192.168.1.0/25 to 192.168.1.127/25. The departmental printer has been placed in another subnet and will be unreachable without a router.
9. A new department has been established with 511 hosts that require addresses. Currently the company uses the 10.20.0.0/16 address space. How many bits must the network administrator borrow to provide addresses for this subnet without wasting addresses?
Explanation: The new department requires 511 hosts, but in any subnet, two addresses (network and broadcast) are unusable, so a subnet must be created that can accommodate 513 addresses. The closest matching number would be a network with 1024 hosts. To create 1024 hosts requires 10 host bits (210–1024). Currently there are 16 host bits available, so the administrator must borrow 6 bits to create 64 subnets, each with 1022 available hosts.
10. A network technician borrows 5 bits from the 10.0.0.0/16 network to create subnets. What is the subnet mask that should be associated with each of the newly created subnets?
Explanation: Currently 16 bits are assigned to the network. If the network administrator borrows an additional 5 bits from the host field, 21 bits are now assigned to the network field. For the subnet mask, the first 21 bits (network) would be turned on and the last 11 (host) bits would be turned off. This creates a mask of 11111111.11111111.11111000.00000000 (255.255.248.0).
11. Fill in the blank.
____ provides a more efficient IP address allocation by allowing the use of different-size subnets in the same network.
VLSM. With traditional subnetting, all subnets must be of the same size, wasting a lot of addresses. With VLSM, different subnet masks can be used on different portions of the network, thus providing a more efficient allocation of available address space.
12. A network administrator has borrowed 3 bits from the 10.20.0.0/25 network to create subnets. The administrator then decided to use the first subnet for point-to-point serial WAN connections each requiring two addresses. How many WAN connections can the administrator address using only the first subnet if he is using VLSM?
Explanation: By borrowing 3 bits from the network portion of the original network, the administrator has now assigned 28 bits to the network, leaving only 4 host bits. Each WAN link requires two addresses, but each subnet has two unusable addresses, meaning that each created subnet must have four available hosts. To create subnets with four hosts means that 2 host bits must be available, allowing the administrator to borrow 2 additional bits, creating four subnets each with four hosts.
13. A network administrator has decided to use VLSM to subnet the 10.11.0.0/20 network to provide addresses for two new departments and the point-to-point link that separates the two departments. The first department has 796 users and the second department has 31 users. The WAN link requires only two addresses. Which of the following subnets will provide the required contiguous space and waste the fewest addresses? (Choose three.)
Explanation: To produce a subnet that could accommodate 796 users would require 10 bits (1024 hosts). To accommodate 31 users would require 6 bits (64 hosts). The WAN links require 2 bits (four hosts). Starting with the largest subnet would require borrowing 2 bits, leaving the 10 bits for hosts. This creates a 10.11.0.0/22 network, which includes the range 10.11.0.0/22 – 10.11.251.255/22. The second network requires 6 bits, can start at 10.11.253.0/26, and would run to 10.11.253.63/24. The third network would start at the next available address (10.11.253.64/30) and run until 10.11.253.67/30.
14. What is the primary purpose of subnetting IPv6 address space?
- Conservation of addresses
- Support hierarchical network design
- Minimize network broadcast traffic
- Improve network performance
Explanation: Unlike IPv4 addresses, subnetting IPv6 address space supports the hierarchical, logical design of networks. IPv6 address space in not in short supply.
15. When subnetting IPv6 address space, why is it wise to subnet on a nibble boundary?
- IPv6 is expressed in hexadecimal, and each nibble is one hexadecimal character.
- You can only subnet IPv6 address space on nibble boundaries.
- Subnetting on a nibble boundary is the most efficient use of IPv6 address space.
- Subnetting on a nibble boundary is mandated by the Internet Numbering Authority.
Explanation: Subnetting on nibble boundaries increases the subnets in increments equal to a hexadecimal digit, making the process easier. There is no rule stating that you must subnet at a nibble boundary, nor is it the most efficient use of address space, but this is not a primary concern with the vast amount of addresses that IPv6 supplies.
16. What is the third subnet address of the 2001:0DB8:ACAD::/48 network when borrowing 8 bits (2 nibbles)?
Explanation: With IPv6, each hexadecimal character represents 4 bits. By borrowing 2 nibbles (8 bits), we would increase the second digit in the hextet one hexadecimal digit at a time for each subnet. The third subnet would have the hexadecimal number 2 in the second spot of the subnet hextet.