IPv4 Address Converter

Private IP Ranges — The Often-Misunderstood 172 Block

When you enter an address, the tool displays chips like 'Private,' 'Public,' or 'Loopback.' Private ranges are not routed on the public internet, meaning anyone can use them freely within their own internal network.

CGNAT (100.64.0.0/10) — Why You Can't Trust a User's IP Address

The 100.64.0.0/10 range is a shared space for carriers, neither private nor public. It was created because of IPv4 address exhaustion, allowing carriers to share a single public IP among many subscribers. You'll often get an address from this range on mobile data networks and from some ISPs.

The practical problem is that a single IP address no longer represents a single user. If you block an IP to prevent abuse, you could end up blocking hundreds of innocent users who share the same carrier-grade NAT (CGNAT). Conversely, the assumption that 'same IP means same person' is also false. It's also normal for a user's IP to change frequently in login histories—on mobile networks, a new NAT session can mean a new IP.

• Use IP-based blocking only for short-term rate limiting, not as the basis for permanent bans.
• Detect duplicate sign-ups or abuse using accounts, device IDs, or phone verification, not just IP addresses.
• Port forwarding is impossible behind CGNAT. If you can't access your home server from the outside, check if your IP is in this range first.
• If you see an address starting with 169.254, it's a self-assigned address from a failed DHCP lookup (APIPA). It's a sign of a network connectivity problem.

Why You Should Store IPs as Integers (Database Best Practices)

`192.168.0.1` is a human-readable notation; its true form is the 32-bit integer `3232235521`. This tool converts between these formats because using integers in a database is overwhelmingly advantageous. Instead of 15 bytes for a `VARCHAR(15)`, you only need 4 bytes. More importantly, range queries can use an index. If you store it as a string, checking if 'this IP belongs to this range' requires a `LIKE` query, which is neither accurate nor fast.

-- Must be UNSIGNED. A regular INT will treat IPs from 128.0.0.0 and up as negative numbers, silently breaking queries.
CREATE TABLE access_log (
  id BIGINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
  ip INT UNSIGNED NOT NULL,
  ts DATETIME NOT NULL,
  INDEX idx_ip_ts (ip, ts)
);

-- Store / Retrieve
INSERT INTO access_log (ip, ts) VALUES (INET_ATON('192.168.0.1'), NOW());
SELECT INET_NTOA(ip) FROM access_log WHERE id = 1;

-- Range queries can now use the index (e.g., connections within 192.168.0.0/24)
SELECT COUNT(*) FROM access_log
 WHERE ip BETWEEN INET_ATON('192.168.0.0') AND INET_ATON('192.168.0.255');

The Danger of IP Addresses with Leading Zeros

This tool automatically detects dotted-quad, integer, hexadecimal, binary, and octal formats. This feature is designed to help you convert values like `3232235521` or `0xC0A80001` you might find in logs or code, but it highlights a noteworthy pitfall.

Many systems interpret numbers with a leading zero as octal. Some libraries will read `010.1.1.1` as `10.1.1.1`, while others will read it as `8.1.1.1`. This discrepancy can lead to real security incidents—for example, a validation check might approve an address, thinking 'it's not in the 10.x private range,' while the actual request goes to a completely different destination. This ambiguity has been exploited to bypass Server-Side Request Forgery (SSRF) defenses, and vulnerabilities have been reported in widely-used IP parsing libraries because of it.

On PTR Records and IP Classes

The `in-addr.arpa` address shown in the results is the name used for Reverse DNS (PTR) lookups. The rule is to reverse the octets, which can be confusing. This tool does the reversal for you. A common place where this becomes critical is when running your own mail server. If the sending IP has no PTR record, or if it doesn't match the domain, receiving servers may flag your mail as spam or reject it outright. If your mail isn't getting through even with correct SPF and DKIM, check your PTR record. PTR records must be set by the entity that allocated the IP address (your hosting provider or ISP).

The Class A/B/C display is a historical concept. Since the introduction of Classless Inter-Domain Routing (CIDR) in 1993, routing decisions have been based on prefix length, not class. We show it for reference as it still appears in old documentation and certification exams, but the assumption that 'this is a Class C address, therefore it's a /24' is no longer valid on modern networks.

# PTR lookup — verify the name generated by this tool
dig -x 8.8.8.8 +short
nslookup 8.8.8.8