Cisco Networking/CCENT/Subnetting

This lesson covers subnetting.

Objectives and Skills

Objectives and skills for the subnetting portion of Cisco CCENT certification include:

• Identify the appropriate IPv4 addressing scheme using VLSM and summarization to satisfy addressing requirements in a LAN/WAN environment

Readings

1. Wikipedia: Subnetwork
2. Wikipedia: IPv4 subnetting reference
3. Wikipedia: Classless Inter-Domain Routing
4. Wikipedia: Supernetwork
5. Cisco: IP Addressing and Subnetting for New Users

Multimedia

1. YouTube: Binary Math - CompTIA Network+ N10-005: 1.3
2. YouTube: Subnetting - CompTIA Network+ N10-005: 1.3
3. YouTube: Subnetting, Cisco CCNA, Binary Numbers - Part 1
4. YouTube: Subnetting, Cisco CCNA, Binary Numbers - Part 2
5. YouTube: Subnetting, Cisco CCNA, Binary Numbers - Part 3
6. YouTube: Subnetting, Cisco CCNA, Binary Numbers - Part 4
7. YouTube: Subnetting Cisco CCNA - Part 1 The Magic Number
8. YouTube: Subnetting Cisco CCNA - Part 2 The Magic Number
9. YouTube: Subnetting Cisco CCNA - Part 3 The Magic Number
10. YouTube: Subnetting Cisco CCNA - Part 4 The Magic Number
11. YouTube: Subnetting Cisco CCNA - Part 5 The Magic Number
12. YouTube: Subnetting Cisco CCNA - Part 6 The Magic Number

Activities

1. Review 3com: Understanding IP Addressing: Everything You Ever Wanted To Know. Complete all exercises in Appendix B (page 57).
2. Review EasySubnetting.com subnetting resources and complete multiple subnetting exercises.
3. Generate practice subnetting questions using the TunnelsUp: Subnet Calculator.
4. Play the Cisco: Subnet Troubleshooting Game and practice until you can consistently achieve a high score.
5. Play the Subnetting.net Subnetting Game and practice until you can consistently achieve a high score.
6. Play the Insite: Cisco Subnet Slingshot Game and practice until you can consistently achieve a high score.
7. Review Subnet Ninja: Subnetting How To Guide and verify your answers with the Subnet Calculator
8. Check your Subnets and Masks Online with this Subnetting Calculator and verify that your subnet masks and CIDR is correct.

Lesson Summary

• A subnetwork, or subnet, is a logical, visible subdivision of an IP network.
• The practice of dividing a network into two or more networks is called subnetting.
• An IP address has two fields, a network prefix and a host identifier.
• The network prefix is identified using CIDR notation.
• In IPv4, the network prefix may also be identified using a 32-bit subnet mask in dotted-decimal notation.
• A network is divided into two or more subnetworks by dividing the host identifier field into separate subnet number and host identifier fields.
• All hosts on a subnetwork have the same network prefix.
• Traffic between subnets is exchanged through a router.
• The first address on any given IPv4 network or subnet is reserved for the network itself.
• The last address on any given IPv4 network or subnet is reserved for broadcast.
• The separation of the network prefix/subnet number from the host identifier is performed by a bitwise AND operation between the IP address and the (sub)network mask.
• The number of subnetworks created by subnetting can be calculated as 2ⁿ, where n is the number of bits used for subnetting.
• The number of available hosts on each subnet can be calculated as 2^n-2, where n is the number of bits available for the host identifier.
• Traditionally, the first network, known as subnet zero, and the last network, known as the all-ones subnet, were not used on production networks. This practice was declared obsolete by RFC 1878 in 1995.
• The goal of Classless Inter-Domain Routing was to slow the growth of routing tables on routers across the Internet, and to help slow the rapid exhaustion of IPv4 addresses.
• Classless Inter-Domain Routing is based on variable-length subnet masking (VLSM), which allows a network to be divided into variously sized subnets, providing the opportunity to size a network more appropriately for local needs.
• The benefits of supernetting are conservation of address space and efficiencies gained in routers in terms of memory storage of route information and processing overhead when matching routes.

Key Terms

binary mask

Data that is used for bitwise operations to set multiple bits either on, off or inverted in a single bitwise operation.

bitwise AND

A binary operation that takes two representations of equal length and performs the logical AND operation on each pair of corresponding bits. The result in each position is 1 if the first bit is 1 and the second bit is 1; otherwise, the result is 0.

broadcast address

A logical address at which all devices connected to a multiple-access communications network are enabled to receive datagrams. In IPv4 networks, the broadcast address is the all-ones address, the last address on the network subnet.

network address

The address of a network or subnetwork. In IPv4 networks. the network address is the all-zeros address, the first address on the network subnet.

prefix mask

A subnet mask specified in CIDR notation.

provider-independent address space

A block of IP addresses assigned by a regional Internet registry (RIR) directly to an end-user organization.

routing table

A data table stored in a router or a networked computer that lists the routes to particular network destinations, and in some cases, metrics (distances) associated with those routes.

subnet

A logical, visible subdivision of an IP network.

subnet address

A logically visible subdivision of an IP network.

subnet mask

A bitmask that encodes the (sub)network prefix length in dotted-decimal notation, starting with a number of 1 bits equal to the prefix length, ending with 0 bits, and encoded in four-part dotted-decimal format.

subnetting

The practice of dividing a network into two or more networks.

supernet

An Internet Protocol (IP) network that is formed from the combination of two or more networks (or subnets) with a common Classless Inter-Domain Routing (CIDR) prefix.

variable-length subnet masks (VLSM)

Used to divide a network into variously sized subnets, as opposed to fixed-length subnet masks used in classful addressing.

Review Questions

1. A subnetwork, or subnet, is _____.

   A subnetwork, or subnet, is a logical, visible subdivision of an IP network.
2. The practice of dividing a network into two or more networks is called _____.

   The practice of dividing a network into two or more networks is called subnetting.
3. An IP address has two fields, _____ and _____.

   An IP address has two fields, a network prefix and a host identifier.
4. The network prefix is identified using _____.

   The network prefix is identified using CIDR notation.
5. In IPv4, the network prefix may also be identified using _____.

   In IPv4, the network prefix may also be identified using a 32-bit subnet mask in dotted-decimal notation.
6. A network is divided into two or more subnetworks by _____.

   A network is divided into two or more subnetworks by dividing the host identifier field into separate subnet number and host identifier fields.
7. All hosts on a subnetwork have _____.

   All hosts on a subnetwork have the same network prefix.
8. Traffic between subnets is exchanged _____.

   Traffic between subnets is exchanged through a router.
9. The first address on any given IPv4 network or subnet is _____.

   The first address on any given IPv4 network or subnet is reserved for the network itself.
10. The last address on any given IPv4 network or subnet is _____.

    The last address on any given IPv4 network or subnet is reserved for broadcast.
11. The separation of the network prefix/subnet number from the host identifier is performed by _____.

    The separation of the network prefix/subnet number from the host identifier is performed by a bitwise AND operation between the IP address and the (sub)network mask.
12. The number of subnetworks created by subnetting can be calculated as _____.

    The number of subnetworks created by subnetting can be calculated as 2n, where n is the number of bits used for subnetting.
13. The number of available hosts on each subnet can be calculated as _____.

    The number of available hosts on each subnet can be calculated as 2n-2, where n is the number of bits available for the host identifier.
14. Traditionally, the first network, known as _____, and the last network, known as _____, were not used on production networks. This practice was _____.

    Traditionally, the first network, known as subnet zero, and the last network, known as the all-ones subnet, were not used on production networks. This practice was declared obsolete by RFC 1878 in 1995.
15. The goal of Classless Inter-Domain Routing was to _____.

    The goal of Classless Inter-Domain Routing was to slow the growth of routing tables on routers across the Internet, and to help slow the rapid exhaustion of IPv4 addresses.
16. Classless Inter-Domain Routing is based on _____.

    Classless Inter-Domain Routing is based on variable-length subnet masking (VLSM), which allows a network to be divided into variously sized subnets, providing the opportunity to size a network more appropriately for local needs.
17. The benefits of supernetting are _____.

    The benefits of supernetting are conservation of address space and efficiencies gained in routers in terms of memory storage of route information and processing overhead when matching routes.

Assessments

• Flashcards: Quizlet: CCENT - Subnetting
• Flashcards: Quizlet: Subnet Mask - Mask Bits
• Flashcards: Quizlet: Subnetting
• Quiz: Quizlet: CCENT - Subnetting
• Quiz: Quizlet: Subnet Mask - Mask Bits
• Quiz: Quizlet: Subnetting

See Also

• Internet Protocol Analysis/Subnetting

References

Type classification: this is a lesson resource.

Completion status: this resource is considered to be complete.

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