As far as I understand, I can tell if an organisation is using NAT if they are using private IP address space.
It can be determined that an organization is using private IP address space if its addresses fall into the following ranges, reserved for private uses by Internet standards groups:
10.0.0.0 through 10.255.255.255
169.254.0.0 through 169.254.255.255 (APIPA only)
172.16.0.0 through 172.31.255.255
192.168.0.0 through 192.168.255.255
Am I correct.....? Please correct the logic if it is not correct.
While you are basically correct about which space is considered "private" (see RFC 1918 section 3), I do not think you can make this assumption in your program, for the following reasons:
An organization might be using private addresses, but not be using NAT at all (for example, a completely private intranet)
An organization might be using NAT, but with a reserved public subnet. (Yes, I have seen organizations with IP address space to burn do this.)
Your question is practically incomprehensible, but taking this from the title:
How will i get to know if organisation is using NAT?
You can't.
Related
Suppose you are assigned to design a LAN for an office having 8 departments. Each department will have 28 computers located in different rooms. Perform subnetting assuming class B private IP address.
I suggest using VLAN for each department, you can use this documentation
how to configure VLAN network and also you can view here example architecture.
Once the VLAN configured you can now use the Class B IP addresses depending on your network setup, you can also use this link IP Address and Subnetting Guide.
The question wants you to understand the Class B allocation of private addressing within RFC1918. RFC1918 allocated a single class A, 16 class Bs and an entire block of 256 class Cs. To answer this question (i'm not doing what is clearly your homework for you) You need to seach for all of the address space set aside in RFC1918 and figure out which is class B.
Then, using some of that address space, create subnets sufficient for networks containing 28 hosts on each network. I'm not sure if your professor/instructor is expecting you to make subnets that are just big enough to support that many users or if you are expected to allow for a resonable amount of growth. You might want to clarify.
So I understand that there used to be classful addresses allocated depending on the first octet of an IP a long time ago. Of those classes, private IP address ranges were given in each.
Class A 10.*.*.*
Class B 172.16-31.*.*
Class C 192.168.0-255.*
I understand that according the RFC 1918, because 192.168 technically starts in the class C range, it should be considered 256 class C networks. However, because there are 256 available class C networks in 192.168.xxx.xxx, would it be incorrect to refer to this as 1 class B network?
A 'network' or 'subnet' is a set of ip-numbers that can connect to each other without the use of a router. A class C network has a maximum of 256 such ip-addresses. To get from one subnet to another subnet, a router is required. You can not call the 192.168.xxx.yyy block a single class B subnet, because the hosts at 192.168.1.xxx cannot directly connect to hosts in 192.168.2.xxx. The hosts are in different subnets.
192.168.xxx.yyy is an ip-block of 256 private class C networks. Classed networks assume fixed network masks for particular ip-ranges. So, for the networks in block 192.168.xxx.yyy, classed-only network software will set the network mask to be equivalent to 255.255.255.0 (or /24).
Today most network software ignores the class of the network and will require a network mask for all ip number blocks. For instance, you can use 192.168.0.0 to 192.168.3.255 as a single classless subnet containing 1024 ip-addresses if you use network mask 255.255.252.0
If you get the gateway as the following:
192.168.0.1
255.255.0.0
And a client at
192.168.10.1
255.255.0.0
They will communicate fine.
I ask this same question myself.
Its considered a C class network but can be configured as a B Class while staying in the private range. We need some educated answers to elaborate on this.
i am from non networking background. I suddenly wondered why the companies i worked almost always had the ip's like 192.168.x.x . Why can't they have something like 1.2.3.4
I understand that ip has and there is a concept called subneting.
Also, 192.168.0.0 to 192.168.255.255 seems to used for private use.
Question:
1) How does IP address matters thought all devices are connected to internet through roughter?
Any wisdom pls?
According to RFC 1918, addresses in the 192.168.0.0-192.168.255.255 range are private. Such addresses can be used internally by any network so they're often used inside an organization. They cannot be used on the Internet since they aren't intended to be kept globally unique.
192.168.X.X isn't the only private range defined in the RFC. You might also run into 10.0.0.0 - 10.255.255.255 or 172.16.0.0 - 172.31.255.255
Most other addresses are public, and have to be assigned to the network by a Regional Internet Registrty (RIR).
Without knowing it, you might see a kind of playing around with symmetries and numbers of 1-Bits, it it is likely not by chance that they chose these binary subnet mask prefixes and a chosen number of 1-Bits and their slightly playful positions (in brackets: number of 1-Bits for each nibble of the subnet mask prefix, just my guess what might have been thought of, since these Bit patterns were “sacrificed” for private networks):
00001010 (=02): 10/8
11001100.0001 (=221): 172.16/12
11000000.10101000 (=2021): 192.168/16
10101001.11111110 (=2243): 169.254/16
Further links:
IPv4
CIDR - Classless Inter Domain Routing.
The many 1-Bits for just the automatic IPs might also be swiftly chosen.
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I know that 127.0.0.1 is by convention the loopback address and that there are various address ranges which are reserved for local use.
Is there an IP address that is reserved never to be assigned?
I would like to test that something works when an IP address can't be found, I could just use a local address which isn't used but thought that there may be an address which is reserved for such use.
According to Wikipedia article on reserved addresses, there are 3 test networks intended for use in documentation only.
192.0.2.0/24
198.51.100.0/24
203.0.113.0/24
Any address in one of those ranges (eg 203.0.113.1) should not map to anything, and indeed should fail to route.
Depending on the type of test you are doing, there are other listed addresses and address ranges that could be appropriate for what you are trying to do.
I think you may want to reword your question. The private address segments (10.0.0.0 - 10.255.255.255, 172.16.0.0 - 172.31.255.255, 192.168.0.0 - 192.168.255.255) are commonly referred to as "non-routable" addresses. I think what you are asking for is a reserved IP address that is reserved specifically to never be assigned. As far as I know there is no address that is reserved in this fashion.
Anything in the
10.0.0.0/8
172.16.0.0/12
192.168.0.0/16
ranges will be dropped by any Internet router - they are intended for internal use only and are not routed. There isn't a single address but using one from a block you don't use internally, as long as your router isn't too clever will do the job.
Of course if you have a managed router it may well drop these anyway and not let them go out of the internal network.
RFC-3330 lists these, and lots of other blocks as well
Looking at RFC 3330, I don't see any IPv4 address reserved for a globally non-routable address.
What I would do is assign -- in local DNS -- an unused local network IP address to the name "blackhole.<domain>" (using the appropriate domain) so you are guaranteed a stable address to which no computer will ever respond. Of course, like always when configuring DNS, ensure that no DHCP server is configured to give out the same address.
192.0.2.0
According to http://en.wikipedia.org/wiki/Reserved_IP_addresses
Assigned as "TEST-NET" in RFC 5737 for use solely in documentation and example source code and should not be used publicly.
https://www.rfc-editor.org/rfc/rfc5737
According to https://en.wikipedia.org/wiki/0.0.0.0, the IP address 0.0.0.0 “is a non-routable meta-address used to designate an invalid, unknown or non-applicable target.”
Well, the answers given are more or less correctly. What you can do is to assign some of the special addresses that are commonly only used as net masks. These will never be encountered in the wild as IP-addresses, so are safe - as long as you don't actually try to use them in the wrong circumstances.
The best ones are:
0.0.0.0 - but be careful to not use it to open a socket, since it will then open a socket to the current main interface on the computer
255.255.255.255 - this one is never assigned, so it should be the best sentinel, unless you need to interact with netmasks.
I had a similar question and I went to figure; if I understood properly; to use a non-forwardable network such as : 169.254.0.0/16 or 127.0.0.0/8
http://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml
Will IPv6 work for your purposes? It looks like IPv6 has a whole range specifically reserved for blackhole usage: 100::/64
So, specifically, 100:: should work.
Wikipedia reference: https://en.wikipedia.org/wiki/IPv6_address#Special_addresses
RFC: https://datatracker.ietf.org/doc/html/rfc6666
depending on what the test is you might be able to use the subnet broadcast address.
i.e.
network = 192.168.1.0 /24
broadcast = 192.168.1.255
For IPV4 the non-routable addresses ranges are from 10.1.1.1 to 10.255.255.254, from 172.16.1.1 to 172.31.255.254, and from 192.168.1.1 to 192.168.255.254. These IP addresses will not be recognized outside of a private network.
Conventional IPv4 dotted quad notation separates the address from the port with a colon, as in this example of a webserver on the loopback interface:
127.0.0.1:80
but with IPv6 notation the address itself can contain colons. For example, this is the short form of the loopback address:
::1
How are ports (or their functional equivalent) expressed in a textual representation of an IPv6 address/port endpoint?
They work almost the same as today. However, be sure you include [] around your IP.
For example : http://[1fff:0:a88:85a3::ac1f]:8001/index.html
Wikipedia has a pretty good article about IPv6: http://en.wikipedia.org/wiki/IPv6#Addressing
The protocols used in IPv6 are the same as the protocols in IPv4. The only thing that changed between the two versions is the addressing scheme, DHCP [DHCPv6] and ICMP [ICMPv6]. So basically, anything TCP/UDP related, including the port range (0-65535) remains unchanged.
Edit: Port 0 is a reserved port in TCP but it does exist. See RFC793
Wikipedia points out that the syntax of an IPv6 address includes colons and has a short form preventing fixed-length parsing, and therefore you have to delimit the address portion with []. This completely avoids the odd parsing errors.
(Taken from an edit Peter Wone made to the original question.)
They're the same, aren't they? Now I'm losing confidence in myself but I really thought IPv6 was just an addressing change. TCP and UDP are still addressed as they are under IPv4.
I'm pretty certain that ports only have a part in tcp and udp. So it's exactly the same even if you use a new IP protocol
I would say the best reference is Format for Literal IPv6 Addresses in URL's where usage of [] is defined.
Also, if it is for programming and code, specifically Java, I would suggest this readsClass for Inet6Address java/net/URL definition where usage of Inet4 address in Inet6 connotation and other cases are presented in details. For my case, IPv4-mapped address Of the form::ffff:w.x.y.z, for IPv6 address is used to represent an IPv4 address also solved my problem. It allows the native program to use the same address data structure and also the same socket when communicating with both IPv4 and IPv6 nodes. This is the case on Amazon cloud Linux boxes default setup.