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🌐 Subnet Reference Table¤

Bảng tham chiếu nhanh cho CIDR, Subnet Mask, Wildcard, và phân loại theo Class A/B/C/D.
Dữ liệu đầy đủ từ /0 đến /32 — tiện cho tra cứu khi học subnetting, network design, hoặc CCNA.

🧮 CIDR to Subnet Mask Reference¤

CIDR Subnet Mask HEX Mask # of IPs Wildcard Mask Host Bits Class
/32 255.255.255.255 FF.FF.FF.FF 1 0.0.0.0 0 Single Host
/31 255.255.255.254 FF.FF.FF.FE 2 0.0.0.1 1 1/1 C
/30 255.255.255.252 FF.FF.FF.FC 4 0.0.0.3 2 ½ C
/29 255.255.255.248 FF.FF.FF.F8 8 0.0.0.7 3 ¼ C
/28 255.255.255.240 FF.FF.FF.F0 16 0.0.0.15 4 ⅛ C
/27 255.255.255.224 FF.FF.FF.E0 32 0.0.0.31 5 1/16 C
/26 255.255.255.192 FF.FF.FF.C0 64 0.0.0.63 6 1/32 C
/25 255.255.255.128 FF.FF.FF.80 128 0.0.0.127 7 1/64 C
/24 255.255.255.0 FF.FF.FF.00 256 0.0.0.255 8 1 C
/23 255.255.254.0 FF.FF.FE.00 512 0.0.1.255 9 2 C
/22 255.255.252.0 FF.FF.FC.00 1,024 0.0.3.255 10 4 C
/21 255.255.248.0 FF.FF.F8.00 2,048 0.0.7.255 11 8 C
/20 255.255.240.0 FF.FF.F0.00 4,096 0.0.15.255 12 16 C
/19 255.255.224.0 FF.FF.E0.00 8,192 0.0.31.255 13 32 C
/18 255.255.192.0 FF.FF.C0.00 16,384 0.0.63.255 14 64 C
/17 255.255.128.0 FF.FF.80.00 32,768 0.0.127.255 15 128 C
/16 255.255.0.0 FF.FF.00.00 65,536 0.0.255.255 16 1 B
/15 255.254.0.0 FF.FE.00.00 131,072 0.1.255.255 17 2 B
/14 255.252.0.0 FF.FC.00.00 262,144 0.3.255.255 18 4 B
/13 255.248.0.0 FF.F8.00.00 524,288 0.7.255.255 19 8 B
/12 255.240.0.0 FF.F0.00.00 1,048,576 0.15.255.255 20 16 B
/11 255.224.0.0 FF.E0.00.00 2,097,152 0.31.255.255 21 32 B
/10 255.192.0.0 FF.C0.00.00 4,194,304 0.63.255.255 22 64 B
/9 255.128.0.0 FF.80.00.00 8,388,608 0.127.255.255 23 128 B
/8 255.0.0.0 FF.00.00.00 16,777,216 0.255.255.255 24 1 A
/7 254.0.0.0 FE.00.00.00 33,554,432 1.255.255.255 25 2 A
/6 252.0.0.0 FC.00.00.00 67,108,864 3.255.255.255 26 4 A
/5 248.0.0.0 F8.00.00.00 134,217,728 7.255.255.255 27 8 A
/4 240.0.0.0 F0.00.00.00 268,435,456 15.255.255.255 28 16 A
/3 224.0.0.0 E0.00.00.00 536,870,912 31.255.255.255 29 32 A
/2 192.0.0.0 C0.00.00.00 1,073,741,824 63.255.255.255 30 64 A
/1 128.0.0.0 80.00.00.00 2,147,483,648 127.255.255.255 31 128 A
/0 0.0.0.0 00.00.00.00 4,294,967,296 255.255.255.255 32 Default Route

🅰️ Class A Subnetting¤

Network Bits Subnet Mask # of Subnets # of Hosts
/8 255.0.0.0 0 16,777,214
/9 255.128.0.0 2 (0) 8,388,606
/10 255.192.0.0 4 (2) 4,194,302
/11 255.224.0.0 8 (6) 2,097,150
/12 255.240.0.0 16 (14) 1,048,574
/13 255.248.0.0 32 (30) 524,286
/14 255.252.0.0 64 (62) 262,142
/15 255.254.0.0 128 (126) 131,070
/16 255.255.0.0 256 (254) 65,534
/17 255.255.128.0 512 (510) 32,766
/18 255.255.192.0 1024 (1022) 16,382
/19 255.255.224.0 2048 (2046) 8,190
/20 255.255.240.0 4096 (4094) 4,094
/21 255.255.248.0 8192 (8190) 2,046
/22 255.255.252.0 16384 (16382) 1,022
/23 255.255.254.0 32768 (32766) 510
/24 255.255.255.0 65536 (65534) 254
/25 255.255.255.128 131072 (131070) 126
/26 255.255.255.192 262144 (262142) 62
/27 255.255.255.224 524288 (524286) 30
/28 255.255.255.240 1048576 (1048574) 14
/29 255.255.255.248 2097152 (2097150) 6
/30 255.255.255.252 4194304 (4194302) 2

🅱️ Class B Subnetting¤

Network Bits Subnet Mask # of Subnets # of Hosts
/16 255.255.0.0 0 65,534
/17 255.255.128.0 2 (0) 32,766
/18 255.255.192.0 4 (2) 16,382
/19 255.255.224.0 8 (6) 8,190
/20 255.255.240.0 16 (14) 4,094
/21 255.255.248.0 32 (30) 2,046
/22 255.255.252.0 64 (62) 1,022
/23 255.255.254.0 128 (126) 510
/24 255.255.255.0 256 (254) 254
/25 255.255.255.128 512 (510) 126
/26 255.255.255.192 1024 (1022) 62
/27 255.255.255.224 2048 (2046) 30
/28 255.255.255.240 4096 (4094) 14
/29 255.255.255.248 8192 (8190) 6
/30 255.255.255.252 16384 (16382) 2

🅲️ Class C Subnetting¤

Network Bits Subnet Mask # of Subnets # of Hosts
/24 255.255.255.0 0 254
/25 255.255.255.128 2 (0) 126
/26 255.255.255.192 4 (2) 62
/27 255.255.255.224 8 (6) 30
/28 255.255.255.240 16 (14) 14
/29 255.255.255.248 32 (30) 6
/30 255.255.255.252 64 (62) 2

🅳️ Class D (Supernets)¤

CIDR Block Supernet Mask # of Class C # of Hosts
/14 255.252.0.0 1024 262,144
/15 255.254.0.0 512 131,072
/16 255.255.0.0 256 65,536
/17 255.255.128.0 128 32,768
/18 255.255.192.0 64 16,384
/19 255.255.224.0 32 8,192
/20 255.255.240.0 16 4,096
/21 255.255.248.0 8 2,048
/22 255.255.252.0 4 1,024
/23 255.255.254.0 2 512