I am now maintaining a piece of code that has a warning not to use the value 0 or 255 in an IP address for hosts.
Can someone help and shed some light on the restriction, if any, on IP address for host? It is mandatory to backup the info from a trusted source.
I found a few sources around the internet but non are official or trusted enough.
The most reliable info I found until now is located at RFC1123 section 2.5 and here at the IANA IPv4 Address Space Registry.
Back in the days of Class A, B, and C addresses, a class C address that ended in .0 referred to the entire subnet, and .255 was the broadcast address for the subnet. So these addresses couldn't be used for individual hosts.
However, address classes became obsolete decades ago, when Classless Inter-Domain Routing (CIDR) was developed to make more efficient use of IP addresses. This is described in RFC 4632. The general idea is that each network has an explicit subnet mask, which need not exactly match octet boundaries in IP addresses. So the assumption that .0 and .255 are the network and broadcast addresses is no longer valid.
I don't know which software / library you're using, but I vaguely remember reading this a few years ago about IP address schemes of days long past. In any way, today there's no such rule.
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(I’m asking the question here because most of the other similar questions on StackExchange seem to be here — please let me know if there is a more appropriate community).
I have a number of computers on a network with a Linux Server running iptables, which is using Network Address Translation.
Not being an expert, I understand that the role of NAT is to take the internal 198 IP addresses, forward them to the external host under a common external IP address, and, when the response arrives, reverse the process.
If a number of internal machines make requests to the same external host, does this mean that host thinks they’re all coming from the same machine? What implications would that have for security or if the host wants to blacklist a machine?
"The router knows where packets belong because The router saves ... an address translation table. It remembers what inside-outside address translations it has made. As such, one inside address equals one outside address, and the out-on-the-internet destination is irrelevant. This, of course, ignores the firewall present in practically every NAT router, which tracks full connections:"
How NAT Port forwarding works
For the idea of private, I mean it like 10.*.*.* idea of ipv4. It seems ipv6 don't conserve ip addresses like these any more.
So, what if I want to create a private subnet which I don't want the others to know my subnet number or access my subnet with ip address. I can create my own range of ip subnet number, but it seems in that way, it would conflicts with global ip address.
I know the idea of link local address, but I think that's useless when I want several links to constitute a network.
If you are just setting up a private local network for development/testing and don't have any actual IPv6 connectivity of your own (or your ISP is stupid and only gave you a /64) then unique local addresses will work fine for you.
However, unique local addresses cannot be used for connectivity to the global Internet. If you need this, you should get global addresses and a proper firewall (as NAT is not needed and strongly discouraged in IPv6).
To get a /48 ULA prefix, visit this generator and throw in a MAC address. (Using a MAC address to generate the prefix is specified by RFC 4193, which defines unique local addresses.)
I have a ipv4 client/server network application written in Qt (v4), which i have to port it in ipv6 (actually the client porting is the most important one), creating in this way a dual-stack ipv4 & ipv6 application.
i do not have any ipv6 network available so as to perform any tests.
i tried the following but with no success:
find a tool that make ipv6 validation: there are not many, usually poorly documented and usually for C language
create a local ipv6 network environment
any ideas?
Definitely create a local IPv6 network environment. A lot of things work the same in IPv6 as in IPv4, but a lot of other things are different. When developing applications that use IPv6 you should have some hands-on experience. You wouldn't expect someone who has never used IP to develop an application that uses IPv4, would you?
Some key differences:
IPv6 addresses are written in hexadecimal
IPv6 hosts will probably have multiple addresses
An IPv6 address that starts with fe80:This is the link-local address. Every IPv6 hosts has one for every interface it has. Link-local addresses exist on every link (ethernet segment, LAN) and they use the same address range on each LAN. It is therefore impossible to route them, but they are very useful when communicating only within the LAN.
One or more IPv6 addresses that start with something in the range 2000: - 3fff:These addresses are the globally routable addresses that you use for normal internet communication.
Zero or more IPv6 addresses that start with something in the range fc00: - fdff:These are Unique Local Addresses (ULA). They are routed within the house, building, organisation etc. They are not routed to the global internet so you cannot reach public services with them.
And of course maybe one or more IPv4 addresses
NAT is (almost) never used with IPv6. ULA addresses are not NATed to a public address.
The best way to get experience is to use an IPv6 connection that is connected to the real IPv6 internet. If your ISP cannot provide you with IPv6 (they should these days, but many ISPs are still slacking) you can use a tunnel broker service like SixXS or Hurricane Electric. They will give you an IPv6-over-IPv4 tunnel with a /48 of addresses. That is enough for 65536 subnets of 2^64 hosts. More than enough for a development network :-) SixXS has the benefit that they provide client software that can run behind a NAT router. Hurricane Electric has the benefit that the registration procedures are much easier.
can one location have more than 1 IP address? I have 2 IP addresses and need to know if they originate from the same source. Thanks
You're missing clear definitions of "location" and "source" in your question but lets go with the assumption that you mean "physical machine" for both (as it's obvious that multiple machines will have different addresses and that a single machine can change its IP address over time).
In that case, the answer is yes. The operating system may bind as many IP addresses to a physical network port (and a single MAC -- the physical addressing used by Ethernet) as it wishes.
Binding multiple IP addresses was the standard way of doing "virtual web hosting" before HTTP/1.1 arrived with the "Host" header. The provider would use DNS to map different host names to different IPs on the same network (usually the same subnet as well) and then assign all of them to the same interface. The webserver would get address information from an incoming connection and based on the local IP address would know which virtual host was being accessed.
This led to a higher-than-typical use of public IP addresses but the practice is now gone with the proliferation of HTTP/1.1.
I'm not sure how Windows presents it, but Linux will present a physical interface with multiple IP addresses as multiple logical interfaces such as "eth0", "eth0:1", "eth0:2", etc. Each logical interface has a unique IP address even though they share the same physical interface.
This is hard to tell. Especially it is hard to tell if these IP addresses are from different times. Today I may have a different IP address than tomorrow.
Even they are from the same time, a load balancer im my internal equipment might send my packets over the fail-over line if the 1st one is overloaded or broken down.
One network adapter normally has only one IP address at once and a typical end user only has one network connection active, but even then the IP address can change. The user could switch from wireless to wired and back or a power outage might reset the ISP's DHCP server (assigning everyone a new IP address).
If you want to identify the user even if his IP address changes, you need to identify the user by his session id, stored in cookies. As two users can have the same IP address (a whole company could be behind a NAT), you should never rely on IP addresses for identification.
I know the RARP protocol is used for mapping physical address to logical address and its some practical applications. Now I have studied RARP(reverse ARP) protocol but cannot find its practical applications. Can anyone give some scenerios and practical applications of RARP protocol.
RARP is now an obsolete protocol that was used to allow a host to determine it's IP address based on the host's MAC address. The protocol was rendered obsolete by more modern techniques and protocols such as BOOTP and DHCP (Dynamic Host Configuration Protocol).
It's unfortunate that RARP is obsolete, because it's extremely handy in determining an unknown IP address of a device. If someone sets a static IP on a device, then years later it is forgotten, moved to a different network, found sitting on a shelf and someone wants to use it, you could RARP the MAC address printed on the device to retrieve its IP.