I am trying to identify if given IPs are from same 1024 SUBNET.
192.168.3.1
192.168.2.19
192.168.1.1
The part I got stuck is that SUBNET address size is 1024.
If I am sure, by checking IP addresses we have to use mask of C class? Because IP is in range between 192.168.0.0 and 192.168.255.255.
But the problem is that I am not sure which mask to use.
I found on the internet table of c class addresses, but I am not sure if it's this one.
Is MASK 255.252.0.0 ?
I believe all these IPs are from same subnet.
I used first table in https://www.aelius.com/njh/subnet_sheet.html
Mask for each one is 255.255.252.0 (We convert mask to binary, and on the end
we got 10000000000 - thats exactly 1024 in decimal)
Address I got for each IP after binary multiplication - 192.168.0.0
Related
I know that each IP class has a default network mask (class A: 255.0.0.0, class B: 255.255.0.0 and class C: 255.255.255.0).
I have been reading the subnetting.net tutorial and they use the default (classful) network mask for subnetting (Question Type 2 Written Example), but on the other hand I read all the time that IP classes are obsolete.
What is exactly a default network mask?
Is it needed for subnetting?
Am I confusing concepts? (I suspect I am)
Please help, this is burning my head.
The IP address can never become obsolete a similar anology can be your home address becoming obsolete. The fact that IPv4 addresses are drying up Because there are that many devices in the globe now which is greater than the number of ip's available. That's why we are moving to IPv6...
A subnet mask is a number that defines a range of IP addresses available within a network. A single subnet mask limits the number of valid IPs for a specific network. Multiple subnet masks can organize a single network into smaller networks (called subnetworks or subnets).
For exp a subnet mask of 255.255.255.0 allows for close to 256 unique hosts within the network (since not all 256 IP addresses can be used).see Why do we need subnet mask?
I am trying to understand the bits which are structured in an IPv4 or CIDR. Reading through RFC documentation I understood that the IP addresses began as 4 octets of made up of 32-bits. I am confused at what a network mask of 255.255.0.0 means?
Even more over if we look at an IP associated with cnn.com
151.101.65.67
Are the individual bits of the IP listed above
01101001.01000001.00110101.00110111
?
Or am I not thinking about this correctly. The network mask has 255.255.0.0 as an example but how would I look at the actuals bits represented in the octets?
The IPv4 address 151.101.65.67 corresponds to the number that can be represented as hexadecimal 0x97654143 or decimal 2539995459. In binary it would be 0b10010111011001010100000101000011. It is shown as 151.101.65.67 for the sake of human readers (decimal 151 = hexadecimal 97 = binary 10010111, etc., notice that you can simply concatenate the hexadecimal or binary representations to form the full number, but not the decimal!)
A network mask determines which part of an IP address corresponds to the network and which part is a host. It "shows" the network part with a binary '1's and "hides" the client part with binary '0's.
The network mask is 'anded' to an IP address and results in the network address. In your example:
IP address (10010111011001010100000101000011) & mask (11111111111111110000000000000000)
is = 10010111011001010000000000000000, or 151.101.0.0
The network mask is usually only relevant locally. Consider a client with IP address 151.101.66.45 and network mask 255.255.255.0 that wants to view a page on your example IP.
The first decision the client needs to make is: can it connect to the address directly (i. e. is it in the same local network?) or does it need to send the request to the router (gateway). By "&"ing its own IP with its own newtwork mask (result = 151.101.66.0) and comparing it with the remote address & its own network mask (result = 151.101.65.0) it determines that both values are not equal, so the request goes to the router for further communication.
Can someone explain exactly how CIDR blocks work and how it translates into 0.0.0.0/32 for example? Please use laymen’s terms or perhaps even an analogy to something not network related. Can’t seems to find an explanation that clicks with me. Thanks!!
Classless Inter-Domain Routing (CIDR) blocks are for specifying a range to IP addresses in format of IPv4 or IPv6. For the sake of simplicity I will explain rest of this in format of IPv4 however it is applicable to IPv6.
General format for CIDR Blocks: x.y.z.t/p
x, y, z and t are numbers from 0 to 255. Basically, each represents an 8 bit binary number. That's why it is range is up to 255. Combination of this numbers becomes an IPv4 IP address that must be unique to be able to identify a specific instance.
In case of AWS, p is a number from 16 to 28. It represents the number of bits that are inherited from given IP address. For example: 10.0.0.0/16 represents an IP address in following format: 10.0.x.y where x and y are any number from 0 to 255. So, actually it represents a range of IP addresses, starting from 10.0.0.0 to 10.0.255.255.
However for each CIDR block, AWS prohibits 5 possible IP addresses. Those are the first 4 available addresses and the last available address. In this case:
10.0.0.0: Network address
10.0.0.1: Reserved for VPC router
10.0.0.2: DNS server
10.0.0.3: Reserved for future use
10.0.255.255: Network broadcast
See here for official doc.
Actually this is one of the main reasons why AWS permits numeric value of p up to /28. Because for p=30, there will be 4 available values however AWS needs 5 IP address to use. In my opinion for p=29, they might found it inefficient to occupy 5 addresses to provide 3 possible IP address.
Number of possible IP addresses can be calculated by using this formula:
NumberOfPossibleIPs = 2^(32-p) - 5
Classless Inter-Domain Routing (CIDR) block basically is a method for allocating IP addresses and IP routing. When you create a network or route table, you need to specify what range are you working in. "0.0.0.0" means that it will match to any IP address. Some IP addresses are specific, like 10.0.0.0, which will match to any IP address beginning with 10. With any IP address range, you can be more specific by using a suffix(something like /32 from your example). These allow the notation to specify number of bits to be used from Prefix(actual IP-range like 10.0.0.0). It represents the bit length of the subnet mask, as indicated above. The subnet mask is like masking when painting. You place a mask over what you DO NOT want to paint on.
For example, 10.10.0.0/16 will have 256 * 256 IP address in its range.
NOTE: Some of the IP address in a range are reserved for various purposes. According to AWS VPC documentation, following are the reserved IP addresses.
10.0.0.0: Network address.
10.0.0.1: Reserved by AWS for the VPC router.
10.0.0.2: Reserved by AWS. The IP address of the DNS server is always the base of the VPC network range plus two; however, we also reserve the base of each subnet range plus two. For VPCs with multiple CIDR blocks, the IP address of the DNS server is located in the primary CIDR. For more information, see Amazon DNS Server.
10.0.0.3: Reserved by AWS for future use.
10.0.0.255: Network broadcast address. We do not support broadcast in a VPC, therefore we reserve this address.
Hope this helps!
All of the above answers are great, but are missing something pretty important for the people who don't understand addressing.
IP addresses are literally just a string of binary, broken up into 4 "octets". Each octet is a 2^8 block; 00000000. So to a machine, an IP address looks like this (with (.) added for human-ness):
00000000(.)00000000(.)00000000(.)00000000
When we're talking about the "mask" on the IP address, it means "the bits that don't change". The /8 or /255.0.0.0 on the end of the block signifies the number of bits that are not allowed to be used by this network.
So, lets say we have a CIDR block of 10.0.0.0/8 - this can also be written in the format 10.0.0.0/255.0.0.0, and you may in fact see this for of notation in older versions of linux. You will also note that 255 is the decimal representation of the binary string 11111111 - 8 binary "ones". So what the machine sees is the following:
Net: 00001010(.)00000000(.)00000000(.)00000000
Mask: 11111111(.)00000000(.)00000000(.)00000000
The part of the mask with 0's is usable address space within the network.
So the following example addresses are valid in this network, because on the 0 parts of the masked range are changing:
00001010(.)00000001(.)00110000(.)00111000
00001010(.)00110001(.)00110100(.)00111001
When we say "cidr block" we simply mean "the human-readable shorthand way of expressing binary strings understood by a machine". In the above example, the first octet can be expressed as 10, and the latter octets 0. And the Mask can be expressed as 255 and the latter octets of 0, or; because the mask is always a sequence of 1's, then a sequence of 0's, the length of the 1's, i.e. 8
And as such, we get a cidr of 10.0.0.0/255.0.0.0, or 10.0.0.0/8
A few more examples:
-- 172.1.1.0/24
net: 10101100.00000001.00000001.00000000
mask: 11111111.11111111.11111111.00000000
^ 24 bits for the mask ^ 8 bits of usable space
-- 10.10.10.8/29
net: 00001010.00001010.00001010.00001000
mask: 11111111.11111111.11111111.11111000
^ 29 bits for the mask. ^ 3 bits of usable space
Importantly though, this is only one aspect of networking. Usually a couple of these are reserved for things. See other answers for AWS specific things. In their examples, the "first 4" ip addresses reserved for AWS will be the first 4 usable addresses, which would be
...00 - Network address
...01 - Router
...10 - DNS
...11 - Futureproofing
Suppose I have following network setup, in a ethernet:
I manually setup start IP and end IP as following:
192.168.2.1 - 192.168.254.254
Manually setup Gateway IP as:
192.168.2.1
Of course, Mask length as:
16
Subnet Mask:
255.255.0.0
Now my question would be following:
Class C network should starting with range: [128, 191], if I'm using 192.*.*.* and setup subnet mask as 255.255.0.0, does it work?
Is there any specific requirement to setup gateway in order to make sure range 192.168.2.1 - 192.168.254.254 work?
For any gateway that: 192.168.2.1 < gateway < 192.168.254.254, it should work for the range?
Suppose within this ethernet, I manually change one's IP to 192.168.1.*, does it able to ping gateway (192.168.2.1)?
Answers:
Since only recently (i. e. about 20 years ago), classful networking is obsolete in favour of CIDR. So you can have an IP range in the old Class A which has a netmask length of 24 bit, or a range in the former Class C range with a netmask length of 16 (or maybe even 17, 18, whatever) bits.
You need a gateway if you want to communicate outside of your network.
The range is defined by the net mask. Even if you only want to use 192.168.2 to 192.168.254, there is no way to exclude 0, 1 and 255 as the third octet, so 192.168.1.* is perfectly reachable from your subnet.
192.168.0.0/24 is address of restricted private IP subset wiki It will work.
Gateway is rather term of specified host within network which has access to other networks. It's address must be accessible from network.
Yes. (Of course if physically connected)
I have around 500 IP addresses. 172.45.67.1 - 172.45.67.200. How do I find the Wifi subnet for these IP addresses? If I could use a java API, that would be great. If not, any other technique to determine the subnet?
Your IP range appears to be part of a Class B IPv4 subnet based on the starting octet value 172.
http://en.wikipedia.org/wiki/IP_address#IPv4_subnetting
As such the subnet mask would be 255.255.0.0.
http://www.subnet-calculator.com/subnet.php?net_class=B
A Class B subnet allows for a maximum of 65,536 addresses.
Your building may be allocated just a slice of that subnet by the people administering that subnet. However, there is no way of knowing how much of that subnet is allocated to the building without further information (if there are 500 addresses, they cannot all be allocated from 172.45.67.* as there are only 255 addresses in that range).