What does the slash mean in an IP address?
In: 53
It starts a CIDR block: a way to determine how many IP address variants should be included in a group based on the IP address in front of the slash.
you talking about something like “255.255.0.0/24”? if your address is the IP address, then the slash value tells the mail man where all people on the street who are helpful enough to assist the mail man in getting directions, or helping in some other way.
Its a shorthand way of writing the subnet mask.
/24 is the same as 255.255.255.0, or when expressed in binary, 11111111.11111111. 11111111.00000000, which is 24 binary 1
Ones in a row, hence /24
It’s used to identify how many other IP addresses are in that group of IPs. A slash 24 says that all IP addresses that have the same first 24 bits are in the same broadcast group. Note: An IP (v4) address has 4 blocks of numbers, separated by a dot(.). Each of these numbers represents 8 bits. For instance 255 means 11111111. So your example of 255.255.0.0/24 says that the first 24 bits must me 11111111.11111111.00000000, then the last 8 bits can be whatever else (mostly).
It’s a CIDR Block.
Basically, an IP address is just a giant series of bits. Something like 192.168.1.1 is actually just 11000000.10100000.00000001.00000001 (dots added for readability).
One important concept with IP addresses is the idea of a network. On a network, everything can technically talk to everything else (although not everything may be listening). From my phone on my network, I can access my computer, my server, my laptop, my streaming stick, and many other devices. They are all on the same network and can talk directly to one another.
However, if I wanted to talk to reddit from my phone, it’s on a different network, so I have to go through my router (often referred to as default gateway) to get there.
My phone knows it’s not on the same network because on top of its IP Address, my phone also has a subnet mask. A typical one would look something like 255.255.240.0, or 11111111.1111111.11110000.00000000 if expanded in binary. My phone knows if something else is on the same network or not if the destination IP address has all the same bits set in the IP address that are also set in the subnet mask.
Now, subnet masks are not the most convenient form to write stuff in all the time, and they are largely (although not necessarily) a direct divide between 1s on the left and 0s on the right, so an alternative notation that is used is the CIDR Block. This is where I might write my network address as “192.168.128.0/24”, where that **/24** represents how many 1’s my subnet mask has.
This is beneficial in a few spots, including making it easier to document, and immediate visibility of how many bits are leftover for actually giving addresses to things.
To explain this, we must first consider Jeri Ryan’s character on Star Trek: Voyager. She was called Seven, or more properly, Seven of Nine. Seven was her individual designation, and the “of Nine” part indicates that she was part of a pod which contained nine total Borg.
So if she wished to communicate with one of the other Borg in her pod, she just sent her message directly to them. “Hello, Five.” “Good morning, Seven, how are you?”
But if she wanted to communicate with another Borg, that was not part of her pod, she had to go through the Borg Collective, and have it route her message to the recipient’s pod, which then got the message to the individual Borg.
The “of Nine” part was necessary because it helped her know if a message could be sent directly to its destination, or if it had to be routed though the collective. If she’d been “Seven of Twenty-Eight” then she’d have had a lot more Borg she could communicate with directly.
In IP addresses, the / is like the word “of” in her name. It lets you know that the individual designation part of this name is over, and subsequent information is regarding the size of your computer’s pod. Of course, we make it far more complicated than it has to be. The number after the / isn’t just the number of computers that your computer can talk to- the bigger the number, the smaller the pod. If it’s “24” then there are 256 addresses in your local pod. If it’s “25” then there are 128. If it’s “23” then there are 512. Each time the number after the / goes down or up, the number of addresses in the local pod doubles or halves.
I want a 5 year old to read these. Interpret them, and then get back to us.
Really the only 5 year old answer is that if there is a slash it’s not an IP address. It’s a range of addresses.
It uses a complicated thing called bitwise comparison on a Subnet mask but until you’re older than 5 you can ignore that.
The number after the slash indicates how big the range of numbers is – lower numbers having a bigger range (not what you might initially think)
The IP at the front indicates where the range will be.
1.2.3.4/32 is a range of one number so the same as 1.2.3.4.
1.2.3.4/8 would have over 16 million ips.
The last number refers to something called a Subnet mask and is used in calculating the number of available addresses in the range.
This notation is useful when carving up an IP range into subnets. Hence the use of a Subnet mask, or the trailing /8 /16 etc.
It denotes a subnet.
Here’s the long and short of it. Your IP is like a house address for your computer. If the IP address tells other computers **where** you live, the subnet or “/“ tells you/other computers the maximum amount of houses that can fit on your street (how many computers can fit on the network).
It would be too complicated to go super into detail but basically
/24 = 254 total computers allowed (most common)
/23 = 510 total computers allowed
/22 = 1022 total computers allowed
/21 = 2046 total computers allowed
And so on.
You can see it multiplies by 2 each time. This is intended because it uses binary to calculate (which exponentially increases.)
Source: Network Engineer
IP addresses are a labelling scheme and that label is like human labels, they have a “first” name and a “family” name. They’re mashed up together and the “/” tells us where the split is. So, if you know the technique to do it (there’s a lot of comments outlining HOW to do that), then you can get each if you need them for whatever reason. So, humans separate our first and last names when writing by using a ” “, whilst the IPv4 convention uses the “/” symbol and a “formula” to get each.
None of these are very 5 year old friendly…
Imagine that everything before the slash is your apartment number, and the number after the slash is how many apartments are in the building. Think of a building with 10 apartments, you’re number 4, so you write 4/10.
This is useful because when you need to find unit 11, you know that it’s not in your building and you’ll need to go outside.
Obviously this is very simplified, for starters the smaller the number after the slash, the bigger your local network is. But you get the idea. Any IP within your local network can be reached directly, and any IP outside of that has to be reached via a router (which is a device that joins multiple networks together).
Latest Answers