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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.
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How can we determine if an IPv6 address is within a private CIDR?
On IPv4 it's straightforward, the subnet and the DNS mask are simple enough to understand.
With IPv6 every resource I find looks like the table below - but my own local IPv6 address starts with fe80, which doesn't seem to conform to the fd00 pattern indicated.
Can anyone help me understand private IPv6 ranges and why my own private IPv6 address would seem not to be in that range?
IPv6 does not have Private addresses the way IPv4 does. IPv6 used to have Site-Local addresses that were analogous to IPv4 Private addresses, but those were deprecated in favor of ULA (Unique Local Addressing), fc00::/7, of which the second half of the addressing, fd00::/8 is available for local assignment, but requires the next 40 bits to be randomly chosen. IPv4 Private addresses and the (deprecated) IPv6 Site-Local addressing were expected to have the same addresses used in multiple sites, but IPv6 ULA is expected to be unique with little chance for duplicate addresses.
What you are looking at is a Link-Local address (in the fe80::/10 range). Packets using Link-Local addresses are confined to a single link, unlike IPv6 Global and ULA addresses. You cannot route packets with Link-Local addresses as all links use the same Link-Local network. You can route ULA addresses, but not on the public Internet. Global addresses are globally routable.
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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Through this website IP to ASN lookup,I can get a series of results about the ASN,but I can't find the meaning of BGP prefix.Maybe I know what it is,however,how it works?
Is there anyone who can tell me the role BGP prefix plays in the ASN system?
A prefix announced in BGP consists of the IPv4 or IPv6 address block being announced and also a path of AS numbers, indicating which ASNs the traffic must pass through to reach the announced address block.
A BGP prefix would look something like (IPv4): 701 1239 42 206.24.14.0/24. The /24 part is referred to as a CIDR mask. The /24 indicates that the first 24 bits in the address block is the ?network? part of the address block.
Robtex provides BGP prefixes for each AS number (ex. https://www.robtex.com/as/as42.html#bgp)
First, let us clarify the relationship among an IP prefix, a route, and BGP NLRI.
The primary function of BGP protocol is to exchange network reachability information (i.e. routes) between BGP speakers. Routes are advertised between BGP peers in BGP update messages.
A route contains 1) a set of destinations as an IP prefix which is carried in the Network Layer Reachability Information (NLRI) field in a BGP update message, and 2) the attributes of the path to the destinations, which is carried in the path attributes field in a BGP update message.
Specifically, in BGP update message, an IP prefix is encoded as a 2-tuple form (length, prefix). Also, BGP has an AS_PATH path attribute which is a list of AS numbers through which the routes in this BGP update message has passed. For more details about how AS_PATH works, you can refer to RFC4271 section 5.1.2.
And of course, a BGP session (eBGP or iBGP) needs to be successfully established in order to exchange BGP update messages.
So now we can summary the answer for your question, a prefix is a part of a BGP route, and will be exchanged between BGP neighbors in a BGP update message.
BGP protocol is responsible to exchange IP blocks advertisement (IP prefixes) between Autonomous Systems.
So when you run a query on Cymru IP tool what you see is the IP blocks advertised on Internet using BGP protocol as they reach Cymru routers. In other words this is the internet routing table from their perspective.
Tools like this has a name: looking glass. There's a lot of LG's on globe as they're a very nice tool to understand how IP blocks spread around Internet. BGP play is another project that uses some LG's to mount a graphic view from the Internet prefixes. Check it: https://stat.ripe.net/bgplay
In BGP, a set of destinations is advertised as an IP prefix, eliminating the concept of network "class" within BGP.
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I'm trying to understand NAT (Network Address Translation) .
Can someone explain how can I determine if my computer is using a NAT (behind a NAT) , or
if it using its own IP address ?
What Barmar said in the comments is the easiest way. Obtaining your IP address over HTTP is indicative that you are behind either a NAT or an HTTP Proxy server. (I suppose it's possible you could have a public IP address, but your device is configured to route HTTP over a caching proxy).
Formal NAT detection and NAT classification can be done with the STUN protocol or equivalent protocol in which a UDP or TCP service echoes back the IP address back to the client that connected to it.
Another telling sign if you are behind a NAT is that your local IP address is in a private IP address range such as the 192.168.x.y range, the 10.x.y.z range, or then 172.16.0.0-172.31.255.255 range.
And pretty much any Wi-Fi setup is going to be a NAT configuration.
The NAT detection technique is based on two observations about the IP TTL (Time To Live) field.
Host operating systems have characteristic initial TTL values. This property of individual operating system implementations of TCP/IP is well known and can be used as part of a "fingerprint" to identify the operating system that a host is running merely by examining its traffic.
NAT devices or gateways decrement the TTL on packets that they forward.
For more details visit: http://www.sflow.org/detectNAT/
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We have a computer that needs to communicate with two routers over one physical ethernet interface. I know this sounds weird, but each router is actually interfaced to an Iridium L Band receiver/transmitter, and we are hoping to double our bandwidth by using two.
I would like to be able to select which link to send data over at the application level, but I'm not quite sure how to do it. My first thought was to establish a virtual IP address in addition to the pre-configured static IP address and use two separate sockets to send() data out over each "interface" separately. My question is, how do I make it so that only one of the routers actually routes the data out to a remote host? The IP addresses and subnet masks of the Iridium transceivers are configurable. Is it possible to make one transceiver only listen to the data coming from one computer IP address? Subnets maybe?
Create vlan inter faces in your machine
ip link add link eth0 name eth0.1 type vlan id 10
ip link add link eth0 name eth0.2 type vlan id 20
assign ip address to eth0.1 and eth0.2 in two networks. Later you can choose which one to bind at application level.
say like this
ifconfig eth0.1 192.168.10.2/24 up
ifconfig eth0.2 192.168.20.2/24 up
Then configure your router in two networks rather than one. Your computer and the routers should be connected to trunk port in the switch. Configure your routers to be in two networks rather than same. Configure subinterfaces in routers so that they listen for vlan 10 and 20 respectively. (how exactly to do this depends on the type of router) I can give you commands only for cisco.