Cheat Sheet Subnetting

Cheat Sheet Subnetting

Referensi cepat untuk menghitung subnet, VLSM, dan memahami notasi CIDR dalam jaringan komputer.

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1. Pengertian Subnet Mask

Subnet mask adalah angka 32-bit yang digunakan untuk membagi jaringan IP menjadi segmen-segmen lebih kecil (subnet).

Subnet mask terdiri dari:

• Bagian Network (1) — menentukan alamat jaringan
• Bagian Host (0) — menentukan alamat host dalam jaringan

Contoh:

IP Address    : 192.168.1.10
Subnet Mask   : 255.255.255.0  =  /24
               (11111111.11111111.11111111.00000000)

Network bits  : 24 (semua 1)
Host bits     : 8  (semua 0)

Kelas IP Address:

Kelas	Range	Default Mask	Penggunaan
A	1.0.0.0 – 126.255.255.255	/8 (255.0.0.0)	Jaringan besar
B	128.0.0.0 – 191.255.255.255	/16 (255.255.0.0)	Jaringan menengah
C	192.0.0.0 – 223.255.255.255	/24 (255.255.255.0)	Jaringan kecil
D	224.0.0.0 – 239.255.255.255	—	Multicast
E	240.0.0.0 – 255.255.255.255	—	Riset/Eksperimental

IP Private (RFC 1918):

Range	CIDR	Penggunaan
10.0.0.0 – 10.255.255.255	10.0.0.0/8	LAN besar
172.16.0.0 – 172.31.255.255	172.16.0.0/12	LAN menengah
192.168.0.0 – 192.168.255.255	192.168.0.0/16	LAN rumah/kantor

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2. Tabel Subnet Lengkap (/24 sampai /30)

Class C (/24 – /30)

CIDR	Subnet Mask	Jumlah Host	Jumlah Subnet*	Blok
/24	255.255.255.0	254	1	256
/25	255.255.255.128	126	2	128
/26	255.255.255.192	62	4	64
/27	255.255.255.224	30	8	32
/28	255.255.255.240	14	16	16
/29	255.255.255.248	6	32	8
/30	255.255.255.252	2	64	4

*Jumlah subnet dari network /24

Rumus Penting:

• Jumlah Host = 2^(host bits) - 2
• Jumlah Subnet = 2^(subnet bits)
• Blok Size = 256 - nilai oktet terakhir subnet mask

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3. Cara Menghitung Network Address, Broadcast, Host Range

Langkah-langkah:

Contoh: IP = 192.168.1.130, Subnet Mask = 255.255.255.192 (/26)

Langkah 1: Temukan blok size

Oktet terakhir subnet mask = 192
Blok size = 256 - 192 = 64
Blok-blok: 0, 64, 128, 192, 256...

Langkah 2: Temukan network address

130 berada di antara 128 dan 192
→ Network Address = 192.168.1.128

Langkah 3: Hitung broadcast

Broadcast = Network Address + Blok Size - 1
           = 128 + 64 - 1 = 191
→ Broadcast = 192.168.1.191

Langkah 4: Tentukan host range

Host pertama = Network Address + 1 = 192.168.1.129
Host terakhir = Broadcast - 1     = 192.168.1.190
Host range: 192.168.1.129 – 192.168.1.190

Ringkasan:

Info	Nilai
Network Address	192.168.1.128
Subnet Mask	255.255.255.192 (/26)
Host Pertama	192.168.1.129
Host Terakhir	192.168.1.190
Broadcast	192.168.1.191
Jumlah Host	62

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4. Tabel Subnet Visual /24

Network: 192.168.1.0/24 dibagi menjadi beberapa subnet:

Dibagi jadi 2 subnet (/25):

Subnet	Network	Host Range	Broadcast
Subnet 1	192.168.1.0	.1 – .126	192.168.1.127
Subnet 2	192.168.1.128	.129 – .254	192.168.1.255

Dibagi jadi 4 subnet (/26):

Subnet	Network	Host Range	Broadcast
Subnet 1	192.168.1.0	.1 – .62	192.168.1.63
Subnet 2	192.168.1.64	.65 – .126	192.168.1.127
Subnet 3	192.168.1.128	.129 – .190	192.168.1.191
Subnet 4	192.168.1.192	.193 – .254	192.168.1.255

Dibagi jadi 8 subnet (/27):

Subnet	Network	Host Range	Broadcast
1	192.168.1.0	.1 – .30	.31
2	192.168.1.32	.33 – .62	.63
3	192.168.1.64	.65 – .94	.95
4	192.168.1.96	.97 – .126	.127
5	192.168.1.128	.129 – .158	.159
6	192.168.1.160	.161 – .190	.191
7	192.168.1.192	.193 – .222	.223
8	192.168.1.224	.225 – .254	.255

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5. Contoh Soal VLSM

VLSM (Variable Length Subnet Mask) adalah teknik subnetting yang menggunakan subnet mask berbeda-beda sesuai kebutuhan host.

Soal:

Sebuah SMK memiliki network 192.168.10.0/24. Bagi menjadi subnet untuk:

• Lab Komputer: 50 host
• Ruang Guru: 25 host
• Ruang TU: 10 host
• Link WAN Router-ISP: 2 host

Penyelesaian VLSM:

Urutkan dari kebutuhan host TERBESAR:

1. Lab Komputer: 50 host → /26 (62 host)
2. Ruang Guru: 25 host → /27 (30 host)
3. Ruang TU: 10 host → /28 (14 host)
4. Link WAN: 2 host → /30 (2 host)

Alokasi subnet:

Departemen	Kebutuhan	CIDR	Network	Host Range	Broadcast
Lab Komputer	50 host	/26	192.168.10.0	.1 – .62	192.168.10.63
Ruang Guru	25 host	/27	192.168.10.64	.65 – .94	192.168.10.95
Ruang TU	10 host	/28	192.168.10.96	.97 – .110	192.168.10.111
Link WAN	2 host	/30	192.168.10.112	.113 – .114	192.168.10.115
Sisa (cadangan)	—	—	192.168.10.116	—	192.168.10.255

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6. Tabel CIDR Lengkap

IPv4 CIDR Reference:

CIDR	Subnet Mask	Host Bits	Jumlah Host	Jumlah Alamat
/8	255.0.0.0	24	16,777,214	16,777,216
/9	255.128.0.0	23	8,388,606	8,388,608
/10	255.192.0.0	22	4,194,302	4,194,304
/11	255.224.0.0	21	2,097,150	2,097,152
/12	255.240.0.0	20	1,048,574	1,048,576
/13	255.248.0.0	19	524,286	524,288
/14	255.252.0.0	18	262,142	262,144
/15	255.254.0.0	17	131,070	131,072
/16	255.255.0.0	16	65,534	65,536
/17	255.255.128.0	15	32,766	32,768
/18	255.255.192.0	14	16,382	16,384
/19	255.255.224.0	13	8,190	8,192
/20	255.255.240.0	12	4,094	4,096
/21	255.255.248.0	11	2,046	2,048
/22	255.255.252.0	10	1,022	1,024
/23	255.255.254.0	9	510	512
/24	255.255.255.0	8	254	256
/25	255.255.255.128	7	126	128
/26	255.255.255.192	6	62	64
/27	255.255.255.224	5	30	32
/28	255.255.255.240	4	14	16
/29	255.255.255.248	3	6	8
/30	255.255.255.252	2	2	4
/31	255.255.255.254	1	0 (point-to-point)	2
/32	255.255.255.255	0	1 (host route)	1

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7. Tips Cepat Subnetting

Rumus Cepat:

Yang dicari	Rumus
Jumlah host usable	2^h - 2 (h = host bits)
Jumlah subnet	2^s (s = subnet bits dipinjam)
Blok size	256 - nilai oktet subnet mask
Network address	IP AND subnet mask
Broadcast	Network + blok size - 1

Trik Menghafal Blok Size:

/25 → 128  (256/2)
/26 → 64   (256/4)
/27 → 32   (256/8)
/28 → 16   (256/16)
/29 → 8    (256/32)
/30 → 4    (256/64)

Nilai Oktet Subnet Mask → CIDR:

Nilai	CIDR (oktet 4)
0	/24
128	/25
192	/26
224	/27
240	/28
248	/29
252	/30
254	/31
255	/32