Understanding Unconventional IP Addresses

From the Market Motive Forums: What does it mean when an IP address is appended with /24?

Why Does My IP Have /24
When you get sent an IP address with a slash, or three parts instead of four, it can be a bit surprising.

An IPv4 address is a 32 bit number. By convention we write it as 4 octets separated by dots, because this makes it easier for humans to grok.

Thus a full IP is 72.1.46.37. We call each number an octet because it’s 8 bits (8×4=32) and thus can have a value of 0->255.

Another component of TCP/IP is the netmask, which tells the stack whether the address is local to the network, or foreign and thus must be routed over the internet. Due to the way netmasks work, we only care about the number of bits they contain and we start counting from the top of the 32 bit number. A netmask is specified using the convention /[number of bits] and we know we’re counting this from the top bit. Thus 192.168.1.69/24 means we will treat anything within 192.168.1.* as being in the local network, and anything else as foreign and thus should be sent to the router.

So if someone sends you unusual IP addresses with slashes or three parts, they’re using a common shorthand to tell you that the lowest octet for these two IPs is open to change, and it’s still coming from them.

If, for example, you receive 72.1.46/24 and 72.1.47/24 as IP addresses, the filter you want is 72\.1\.46\.* or 72\.1\.47\.* The backslash is needed since the IP address filter is a regexp and the . character has special meaning to regexps. The GA UI may have made this easier and you can now do a simple wildcard like 72.1.46.*, but I’m going from memory.

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