How do I force libcurl to access a server running in dual stack mode over either ipv4 or ipv6? It shouldn't be hard to do using IPs addresses, but I'm looking for something that works with DNS ...
You bet. The config CURLOPT_IPRESOLVE which can be set to CURL_IPRESOLVE_V4 or CURL_IPRESOLVE_V6.
A more robust solution, if you can control DNS in anyway, is to make an A record for the v4 address and a separate AAAA record for the v6 address. This would let you pick the network you want to poll this system by, regardless of DNS resolution. But CURL can do what you want, just fine.
Related
I'm writing a macOS C++ application using Qt that acts as both a UDP client and UDP server. The server functionality allows the user to configure which port the UDP packets will be received on, and the client functionality allows specifying both a target host and a port number. The host can be either a hostname or an IP address, including addresses or hostnames that resolve to a multicast or broadcast address.
In order to help prevent circularity, when the server functionality is enabled I need to be able to warn the user when the host and port they've entered for the client would send the packets directly to the app's server. Of course it's easy to check if the port numbers match, but this means I need to know whether the host they've entered refers to the current system.
Examples of hostnames or IP addresses that would typically be problematic:
127.0.0.1
localhost
192.168.1.255 (assuming the system is on a 192.168.1.0/24 subnet)
any of the IP addresses assigned to the current system's network interfaces
the system's local DNS name
any other loopback addresses that may be configured other than 127.0.0.1
How could I go about detecting this?
Since this app is being written using Qt, a solution that exclusively uses Qt's framework would be ideal. But if that's not possible (since Qt doesn't handle every possible use case) a macOS-specific solution will work too.
QNetworkInterface class should provide the most information you may need.
You can obtain a list of IP addresses using QNetworkInterface::allAddresses() static function.
You can also get a list of all interfaces using QNetworkInterface::allInterfaces().
Calling QNetworkInterface::addressEntries() for each QNetworkInterface returned by QNetworkInterface::allInterfaces() will give you more information about address entries for each interface.
auto ifs = QNetworkInterface::allInterfaces();
foreach (auto interface , ifs){
auto addresses = interface.addressEntries();
foreach ( auto addy , addresses){
///play with the addy here.
}
}
You can also test hostnames against those ip addresses which you are going to ban, using QDnsLookup class.
Lets say my IP currently is: 123.123.123.123
How can I get that string programmatically?
Note: I don't want to get this IP: 192.168.0.10, I want that IP which others can use to connect into my computer via HTTP or anything.
NOTE: I dont want to open some web-page such as ip4.me to get the address, I want to get it with just C++.
I tried to google but every suggestion was "load a page and read the IP it tells you". Is that really the only way?!
You can fetch it from http://api.externalip.net/ip/ or some similar services, but I'm not sure how reliable these sites are, in means of availability
Any other way would be extremely complicated, as in general, no network equipment has api to tell external IP, and even if it had, you can not tell is there a simple xDSL router in front of you or Cisco ASA nating outbound traffic
My recommendation is to send a packet with the record route option.
If you know your upstream gateway, you should be able to find a ping command that allows you to set record route, and then either stores that data in an array or something you can regex.
Your WAN IP should be either record 0 or record 1, I believe.
What network library are you using?
How can I get all the IP addresses and associated host names in a LAN?
To get the list of interfaces and IP addresses, use getifaddrs().
Search for interfaces with ifa_addr->sa_family == AF_INET
The IP address is in sin_addr.s_addr.
You can then use gethostbyaddr() to look up the DNS name for that IP address.
Update:
It was pointed out to me that the OP was probably asking about discovering other hosts, rather than the addresses of interfaces on the local machine.
There is no reliable way to discover other machines on the local area network, but there are a couple of tricks.
Ping method: Use the ping utility (or a programatic equivalent) to ping the local broadcast address, then see who responds. The broadcast address can be found by listing the interfaces as shown above. I believe ICMP does not require root access under OSX. Note that many systems may have ICMP ping disabled or firewalled, so you will only get responses from the non-stealth ones.
ARP method: Check the system ARP cache to see what IP addresses have been recently active. This will only show systems which have broadcast packets on the same network segment in recent minutes.
Both methods can be blocked by firewalls, routers, and even switches, so the exact borders of the "LAN" can be pretty narrow. Both methods can be implemented programmatically, but it might be simpler and more portable to just call out to the command line ping or arp commands.
I need to be able to find the IP address of the server the page is currently executing on. I have some code that calls a third party site and has to pass a specific key that changes depending on which server it is on. Is there a CGI variable or some way in ColdFusion to determine what the IP address is of the host server?
Like the other commenters have outlined if you need the external IP as the third party site sees it then you probably should use the external approaches they recommend.
However if the third party is giving you access in some form that is based on an actual IP as the Server sees itself and not the IP as they see it you can use
<cfset cName = CreateObject("java", "java.net.InetAddress").getLocalHost().getHostAddress()>
<cfdump var="#cName#">
There are two reasons why a program can't query the host it's running on and see what its IP is:
It might have multiple ips, and short of looking through all sorts of kernel data structures you're unlikely to know which one is going to be used for a given outgoing connection.
It might connect to the outside world though a NAT firewall or some sort of proxy so that the outside world will see a different IP than any of the ones configured on your box.
Actually, there might be more than those two, but those are ones that have occurred to me.
Because of that, the simplest way is to connect to another box somewhere outside of your corporate network and see what IP it thinks you have. I use a two line CGI script running on my colo box to detect what IP my home server currently has (so I can detect when the cable company changes it).
You can use CGI.LOCAL_ADDR to determine the IP-address of your server (CFML equivalent to PHP's $_SERVER["SERVER_ADDR"]). It works on IIS and Apache using ColdFusion or Railo, given you are not behind a Proxy, not natting your server IP and having only one IP assigned to your server (not sure which IP would be shown, if there are more than one).
I would use hostip.info API
Your IP in XML: http://api.hostip.info/get_xml.php
Your IP in HTML: http://api.hostip.info/get_html.php
The safest way will be to use a service like WhatIsMyIP. If the server is behind a NAT, then the OS has no knowledge of the external IP address.
There are many questions in SO regarding this, see here for example.
<cfhttp url="http://www.whatismyip.com/" result="myresult" resolveurl="yes">
<cfoutput>#myresult.filecontent#</cfoutput>
I have a network of computers that they will connect to the a server with DHCP, so I don't know what Ip address a computer will get when I connects to the server. If 192.168.0.39 for example is connected to the server can I identify the real computer behinde this ip address? ( I can install an external application on each client in order to send some data to server for example mac address or so... )
If you are responsible for the DHCP server, you can configure it to hand out a specific IP to a specific MAC. Having done that, you can be reasonably confident of that mapping -- it is possible to spoof MACs, so if you are worried about security, you'll need a much more heavy duty approach. If this is a casual application where the risk of that is low, you configure your DHCP server to hand out IPs based on MACs and then make use of those mappings in your application.
You might not even need the IP address. On an Ethernet network, all communication from a computer, whether it's IPv4, IPv6, or even IPX will be labelled with a MAC address that's stable over time and unique per network card.