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How many bits must be borrowed from the host portion of an address to accommodate a router with five connected networks?

• two
• three
• four
• five

To determine how many bits must be borrowed from the host portion of an IP address to accommodate a router with five connected networks, we need to understand a few fundamental concepts related to subnetting in IP addressing.

IP Addressing and Subnetting

An IP address is typically divided into two parts: the network portion and the host portion. The network portion identifies the specific network, while the host portion identifies individual devices (hosts) within that network. Subnetting is the process of dividing a larger network into smaller, more manageable sub-networks (subnets). This is often done to improve network performance, enhance security, or accommodate a specific organizational structure.

When subnetting a network, we borrow bits from the host portion of an IP address to create additional subnets. The number of bits borrowed determines how many subnets can be created and how many hosts each subnet can support.

Requirements for Subnetting

To solve the problem of accommodating five connected networks, we need to determine how many subnets are required. Each network will represent a different subnet. Since we need five subnets, we must borrow enough bits from the host portion to create at least five subnets.

Calculating the Number of Subnets

The formula to calculate the number of subnets that can be created by borrowing n bits from the host portion is:

Number of Subnets = 2ⁿ

Where n is the number of bits borrowed.

• If we borrow 2 bits: 2² = 4 subnets.
• If we borrow 3 bits: 2³ = 8 subnets.
• If we borrow 4 bits: 2⁴ = 16 subnets.
• If we borrow 5 bits: 2⁵ = 32 subnets.

We need at least five subnets, so borrowing 2 bits would not be sufficient since it would only give us 4 subnets. Borrowing 3 bits, however, gives us 8 subnets, which is enough to accommodate the five connected networks.

Conclusion: Three Bits Must Be Borrowed

Correct Answer: Three bits must be borrowed from the host portion of an address to accommodate a router with five connected networks.

Detailed Explanation

Step-by-Step Process

1. Understanding the Requirement:
   • We need 5 subnets for 5 connected networks.
   • This requires borrowing bits from the host portion of the IP address.
2. Applying the Formula:
   • We know that the number of subnets = 2ⁿ, where n is the number of bits borrowed.
   • For n = 2, 2² = 4 subnets (Not sufficient, since we need at least 5 subnets).
   • For n = 3, 2³ = 8 subnets (Sufficient to cover 5 subnets).
3. Understanding the Impact on Host Addresses:
   • Borrowing more bits reduces the number of host addresses available in each subnet.
   • For example, if you borrow 3 bits, the remaining bits in the host portion determine the number of hosts per subnet.
   • If the original network is a Class C address (with a default subnet mask of 255.255.255.0), borrowing 3 bits would change the subnet mask to 255.255.255.224.
   • This leaves 5 bits for host addresses, allowing 2⁵ – 2 = 30 usable host addresses per subnet (subtracting 2 for the network and broadcast addresses).
4. Scalability:
   • By borrowing 3 bits, not only do we satisfy the requirement of 5 subnets, but we also have some room for future expansion (up to 8 subnets).
   • If you anticipate growth or the need for additional networks, this is a flexible and efficient solution.
5. Practical Implications:
   • In real-world scenarios, planning for future network growth is crucial. By choosing to borrow 3 bits, network administrators can ensure that the network can scale without needing to reconfigure the entire IP scheme.
   • Proper subnetting also enhances security by isolating different networks, reducing broadcast traffic, and making it easier to implement access control lists (ACLs).

Additional Considerations

Efficiency: Borrowing too few bits (like 2) would result in an insufficient number of subnets, leading to a scenario where additional subnetting would be required later on. This could cause network disruptions and additional administrative overhead.

Overhead: Borrowing more bits than necessary could result in underutilization of IP addresses within each subnet, which might be a waste of resources, especially in networks with a large number of hosts.

Real-World Example

Consider a small office network where a single router connects several departments, each requiring its own subnet. If there are five departments, the network administrator must ensure that the router can handle at least five subnets. By borrowing 3 bits from the host portion of the IP address, the administrator can configure the router to manage these subnets efficiently.

Conclusion

The correct answer to the question is that three bits must be borrowed from the host portion of an address to accommodate a router with five connected networks. This allows for the creation of 8 subnets, ensuring that the 5 required subnets are met with additional capacity for future expansion. This solution balances the need for subnetting with the availability of host addresses, making it an optimal choice for network configuration.