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Zorluk: ZorIPv4 Addressing and Subnetting

A network engineer is configuring Variable Length Subnet Masking (VLSM) within the assigned block 10.200.16.0/2010.200.16.0/20. The first subnet (Subnet A) must be allocated from the start of the block to support at least 600600 usable host interfaces. The second subnet (Subnet B) must be provisioned immediately following the address space allocated to Subnet A to accommodate at least 250250 usable host interfaces. What is the decimal value of the third octet in the network ID of Subnet B?

Cevap: 20

Cevap

The decimal value of the third octet in the network ID of Subnet B is 20.
To support at least 600 usable hosts in Subnet A, 10 host bits are required (210−2=10222^{10} - 2 = 1022 usable addresses), establishing a /22 subnet mask. With a /22 prefix starting at 10.200.16.010.200.16.0, the block spans 4 values in the third octet (16,17,18,1916, 17, 18, 19), covering 10.200.16.010.200.16.0 through 10.200.19.25510.200.19.255. The next available network address for Subnet B starts immediately at 10.200.20.010.200.20.0. Thus, the third octet decimal value is 20.

Adım Adım Çözüm

1
Determine the required prefix length for Subnet A.
Subnet A requires a /22 prefix length.
Subnet A needs at least 600 usable host IPs. Since 29−2=5102^9 - 2 = 510 is insufficient, 10 host bits are required (210−2=10222^{10} - 2 = 1022). The prefix length is 32−10=2232 - 10 = 22.
2
Calculate the block size and address range for Subnet A.
Subnet A spans 10.200.16.010.200.16.0 to 10.200.19.25510.200.19.255.
A /22 prefix has a block size of 2(32−22)=10242^{(32-22)} = 1024 total addresses (44 block increments in the third octet). Starting at 10.200.16.010.200.16.0, the subnet ends at 10.200.19.25510.200.19.255.
3
Find the starting network ID for Subnet B.
Subnet B begins at 10.200.20.010.200.20.0.
Subnet B must be allocated immediately after the broadcast address of Subnet A (10.200.19.25510.200.19.255).
4
Extract the third octet value.
20
In the IPv4 address 10.200.20.010.200.20.0, the third octet is 20.

Anahtar Kavram

Variable Length Subnet Masking (VLSM) block size calculation and sequential subnet allocation.
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Konular

IPv4 Addressing and Subnetting

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