If the client identifier is changed in a device should the server lease a new ip address or use the existing lease which is bound to the mac address and the old client identifier?
I.e. Should the mac address be used as the first alternative regardless of the change in Client Identifier and give the same address?
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I read that in the server site – The local (server) socket address is provided by the OS and the remote (client) socket address is the address of the client that makes the connection. The server can find this socket address when a client tries to connect
to the server but in the Client Site – The local (client) socket address is provided by the OS.
What about the remote (server) socket address?
The client does need some way to find the IP address of the server it wants to connect to; the most common way to find the IP address is by starting with a hostname string (e.g. "stackoverflow.com" or whatever) that was either supplied by the user or hard-coded into the program, and using DNS to look up an IP address that corresponds to that hostname string. The usual API for doing a DNS lookup is getaddrinfo(), although older (or lazier) software might call the older gethostbyname() function instead.
Once the client has the IP address of the server it wants to connect to, it also needs to supply a port number; often the port number just a well-known standard port number for a particular type of service (such as 80 for HTTP, or 22 for SSH). If not, then the client will either have to "just know" what port number to use to contact the server, or it will need some other mechanism to figure out which port number to use.
I am running a TCP/IP server and binding it to INADDR_ANY (0.0.0.0). My network is multi-homed so has multiple local IP addresses. So by using INADDR_ANY, the client can connect to me using any of those local addresses.
I now want to construct a full url with my local IP address. I will send this address to the client and (assuming no NAT-traversal), the client should be able to use the sent address to connect to my server. What socket API can I use to find this address? This address has to be used in the IP packet, so should be discoverable.
There is no common socket API function across platforms for this type of query. You have to use OS-specific APIs instead.
On 'Nix platforms, you can use getifaddrs().
On Windows, you can use GetAdaptersInfo() (XP and earlier), GetAdaptersAddresses() (Vista and later), or WSAIoctl(SIO_GET_INTERFACE_LIST/_EX).
And so on.
So I am kind of new to networking and I'm just interested in the client/server architecture. Let's say you developed a program and the client version ran on a computer and the server version on the server(obviously). In order for the client to connect to the server, it would have to know the ip address of the server (and the port attached so it can be routed to the correct computer/program). Does that mean that the server's ip address can not change? Would you have to specifically tell your ISP to keep the ip address static? Because if both the client and server ip addresses change, then they would have no way to connect and the program wouldn't work... in other words there has to be one constant. When you sign up for a VPS do they give you a static ip address you can bind to from the client version? Thanks!
In order for the client to connect to the server, it would have to know the ip address of the server (and the port attached so it can be routed to the correct computer/program).
Correct.
Does that mean that the server's ip address can not change?
No. In fact, IPs can change at any time. Most servers that are exposed to the public Internet have a static domain name registered in the Internet's DNS system. A client asks DNS to resolve the desired domain name to its current IP address, and then the client can connect to it. But even in private LANs, most routers act as a local DNS server, allowing machines on the same network to discover each other's IP by machine name.
The OS typically handles DNS for you. A client can simply call gethostbyname() or prefferably getaddrinfo(), and the OS will perform DNS queries as needed on the client's behalf and return back the reported IP(s).
Would you have to specifically tell your ISP to keep the ip address static?
You can, but that usually costs extra. And it is not necessary if your server is registered in DNS. And there are free/cheap DNS systems that work with servers that do not have a static IP.
Because if both the client and server ip addresses change, then they would have no way to connect and the program wouldn't work...
That is where DNS comes into play.
in other words there has to be one constant.
A registered domain name that can be resolved by DNS.
When you sign up for a VPS do they give you a static ip address you can bind to from the client version?
It depends on the VPS service, but a more likely scenario would be you are assigned a static sub-domain within the VPS service's main domain. For example, myserver.thevps.com. Or, if you buy your own domain (which can be done very cheaply from any number of providers), you can usually link it to the DNS server operated by your VPS service.
I have been trying to learn socket programming in C++ and got some progress for the basics. But I understood that basics are not fundamentals.
One of those fundamentals is about the question which is stated in the title. Lets say I have two separate applications running on the same computer. One of them has a server socket and the other one has a client.
When the server gets an IP address automatically, how can client find the server? Do I have to assign an IP address that is known by the client? In that case, maybe that IP address is not available on the network.
Or can client find and connect to the server by sone kind of name or id?
Have the server bind to all interfaces and have the client lookup 'localhost' by name; it's resolved locally, (ie. no external DNS service required), to an IP address stored in a 'hosts' file, and is set by default to 127.0.0.1
Google 'hosts file'
The IP address of any server in the same host is 127.0.0.1 unless the server has bound to a specific, different IP address. As #MartinJames points out, you can use 'localhost' as the hostname for that, except on certain broken Linux distributions.
I like to change DNS address of iPhone through my application. Is it possible ? Any one let me know how i can do it, it will be very helpful. Thanks in advance.
If by DNS address you mean the IP address of the DNS server the iPhone uses for queries to resolve the domain name you provide, then it is not possible in a non-jailbreaked device. The IP address of the DNS server is provided to the iPhone through DHCP. So you would therefore have to change the DHCP settings in the setup of the network you connect to, eg. the Wifi access point.
If you want to change the IP address assigned to the iPhone (and possibly provided to other devices through DNS) then again you would have to modify the DHCP settings on your server. This IP address is provided to the iPhone through DHCP and possibly coordinated with the DNS server in the network.
Unfortunately it's not possible from an app. Oh, and I believe you mean IP address, right?
there was a trick to reset an ip address by turning airplane mode on and off, but the ip address is assigned to you by the network you are connecting to. In the apps you don't have a way to request a "reset" like this. this is done on the system level and not exposed as a method an app can use
google up netinfo+ its an app for setting dns on iphone