Network Utilities

IP Lookup, CIDR Calculator, MAC Address Lookup, and Port Number Lookup
Examples:

Network CIDRs

Here's a list of network subnets that cover the given IP range.
# Subnet IP Range Organization / ASN
1 1.2.3.4/30 1.2.3.4 - 1.2.3.7
2 1.2.3.8/29 1.2.3.8 - 1.2.3.15
3 1.2.3.16/28 1.2.3.16 - 1.2.3.31
4 1.2.3.32/27 1.2.3.32 - 1.2.3.63
5 1.2.3.64/26 1.2.3.64 - 1.2.3.127
6 1.2.3.128/25 1.2.3.128 - 1.2.3.255
7 1.2.4.0/22 1.2.4.0 - 1.2.7.255 China Internet Network Infomation Center 24151
8 1.2.8.0/21 1.2.8.0 - 1.2.15.255
9 1.2.16.0/20 1.2.16.0 - 1.2.31.255
10 1.2.32.0/19 1.2.32.0 - 1.2.63.255
11 1.2.64.0/18 1.2.64.0 - 1.2.127.255
12 1.2.128.0/17 1.2.128.0 - 1.2.255.255 TOT Public Company Limited 23969
13 1.3.0.0/16 1.3.0.0 - 1.3.255.255
14 1.4.0.0/14 1.4.0.0 - 1.7.255.255
15 1.8.0.0/13 1.8.0.0 - 1.15.255.255
16 1.16.0.0/12 1.16.0.0 - 1.31.255.255 DAOU TECHNOLOGY 45996
17 1.32.0.0/11 1.32.0.0 - 1.63.255.255 TM Net, Internet Service Provider 4788
18 1.64.0.0/10 1.64.0.0 - 1.127.255.255 HKT Limited 4760
19 1.128.0.0/9 1.128.0.0 - 1.255.255.255 Telstra Corporation Ltd 1221
20 2.0.0.0/15 2.0.0.0 - 2.1.255.255 Orange 3215
21 2.2.0.0/16 2.2.0.0 - 2.2.255.255 Orange 3215
22 2.3.0.0/22 2.3.0.0 - 2.3.3.255 Orange 3215
23 2.3.4.0/30 2.3.4.0 - 2.3.4.3 Orange 3215
24 2.3.4.4/31 2.3.4.4 - 2.3.4.5 Orange 3215
API Call

Get JSON results via command line with either curl or wget.

Try it:
curl "https://steamr.com/1.2.3.4-2.3.4.5" 

[
    {
        "start": "1.2.3.4",
        "end": "1.2.3.7",
        "netmask": "255.255.255.252",
        "maskbits": 30,
        "size": 4
    },
    {
        "start": "1.2.3.8",
        "end": "1.2.3.15",
        "netmask": "255.255.255.248",
        "maskbits": 29,
        "size": 8
    },
    {
        "start": "1.2.3.16",
        "end": "1.2.3.31",
        "netmask": "255.255.255.240",
        "maskbits": 28,
        "size": 16
    },
    {
        "start": "1.2.3.32",
        "end": "1.2.3.63",
        "netmask": "255.255.255.224",
        "maskbits": 27,
        "size": 32
    },
    {
        "start": "1.2.3.64",
        "end": "1.2.3.127",
        "netmask": "255.255.255.192",
        "maskbits": 26,
        "size": 64
    },
    {
        "start": "1.2.3.128",
        "end": "1.2.3.255",
        "netmask": "255.255.255.128",
        "maskbits": 25,
        "size": 128
    },
    {
        "start": "1.2.4.0",
        "end": "1.2.7.255",
        "netmask": "255.255.252.0",
        "maskbits": 22,
        "size": 1024,
        "org": "China Internet Network Infomation Center",
        "asn": 24151
    },
    {
        "start": "1.2.8.0",
        "end": "1.2.15.255",
        "netmask": "255.255.248.0",
        "maskbits": 21,
        "size": 2048
    },
    {
        "start": "1.2.16.0",
        "end": "1.2.31.255",
        "netmask": "255.255.240.0",
        "maskbits": 20,
        "size": 4096
    },
    {
        "start": "1.2.32.0",
        "end": "1.2.63.255",
        "netmask": "255.255.224.0",
        "maskbits": 19,
        "size": 8192
    },
    {
        "start": "1.2.64.0",
        "end": "1.2.127.255",
        "netmask": "255.255.192.0",
        "maskbits": 18,
        "size": 16384
    },
    {
        "start": "1.2.128.0",
        "end": "1.2.255.255",
        "netmask": "255.255.128.0",
        "maskbits": 17,
        "size": 32768,
        "org": "TOT Public Company Limited",
        "asn": 23969
    },
    {
        "start": "1.3.0.0",
        "end": "1.3.255.255",
        "netmask": "255.255.0.0",
        "maskbits": 16,
        "size": 65536
    },
    {
        "start": "1.4.0.0",
        "end": "1.7.255.255",
        "netmask": "255.252.0.0",
        "maskbits": 14,
        "size": 262144
    },
    {
        "start": "1.8.0.0",
        "end": "1.15.255.255",
        "netmask": "255.248.0.0",
        "maskbits": 13,
        "size": 524288
    },
    {
        "start": "1.16.0.0",
        "end": "1.31.255.255",
        "netmask": "255.240.0.0",
        "maskbits": 12,
        "size": 1048576,
        "org": "DAOU TECHNOLOGY",
        "asn": 45996
    },
    {
        "start": "1.32.0.0",
        "end": "1.63.255.255",
        "netmask": "255.224.0.0",
        "maskbits": 11,
        "size": 2097152,
        "org": "TM Net, Internet Service Provider",
        "asn": 4788
    },
    {
        "start": "1.64.0.0",
        "end": "1.127.255.255",
        "netmask": "255.192.0.0",
        "maskbits": 10,
        "size": 4194304,
        "org": "HKT Limited",
        "asn": 4760
    },
    {
        "start": "1.128.0.0",
        "end": "1.255.255.255",
        "netmask": "255.128.0.0",
        "maskbits": 9,
        "size": 8388608,
        "org": "Telstra Corporation Ltd",
        "asn": 1221
    },
    {
        "start": "2.0.0.0",
        "end": "2.1.255.255",
        "netmask": "255.254.0.0",
        "maskbits": 15,
        "size": 131072,
        "org": "Orange",
        "asn": 3215
    },
    {
        "start": "2.2.0.0",
        "end": "2.2.255.255",
        "netmask": "255.255.0.0",
        "maskbits": 16,
        "size": 65536,
        "org": "Orange",
        "asn": 3215
    },
    {
        "start": "2.3.0.0",
        "end": "2.3.3.255",
        "netmask": "255.255.252.0",
        "maskbits": 22,
        "size": 1024,
        "org": "Orange",
        "asn": 3215
    },
    {
        "start": "2.3.4.0",
        "end": "2.3.4.3",
        "netmask": "255.255.255.252",
        "maskbits": 30,
        "size": 4,
        "org": "Orange",
        "asn": 3215
    },
    {
        "start": "2.3.4.4",
        "end": "2.3.4.5",
        "netmask": "255.255.255.254",
        "maskbits": 31,
        "size": 2,
        "org": "Orange",
        "asn": 3215
    }
]