I'm interested in the ip address of remote hosts. Is there an easy way to resolve a host name into its ip address?
After searching in the codename one source code and reading through the documentation, the only way to achieve this seems by implement android/ios native features (e.g. using the InetAddress class).
Yes you would need to implement this using native code or thru the Socket API by implementing the DNS protocol calls.
The InetAddress class can be used in the Android/Desktop ports but other platforms (e.g. iOS) would need the Objective-C/C equivalent of that.
Related
I will need the ability to communicate with a device attached via USB that shows up as a serial port. Is this possible with cn1? I haven't seen any reference to it. Does the native java import javax.comm.*; work on all platforms?
No, comm isn't portable. You would be able to bundle it into the desktop port but you'd need a different implementation for everything else using the native interfaces.
Before we had builtin support for sockets Steve created a cn1lib for socket support which you can use as a reference to how one would implement streaming data over native interfaces
I use getaddrinfo() to get IP Address corresponding to a server using a URL. It essentially sends DNS query to the DNS server. I want to be able to send that query from a particular outbound interface. Basically I have multiple interfaces through which DNS query could be sent out. Currently, getaddrinfo() doesn't have a way to dictate which interface it should use to send out the DNS query. Is the only option to change getaddrinfo() routine? Does anyone know of any other way to achieve this?
The fundamental issue with the question is that you seem to expect getaddrinfo to work with DNS only, and then to be able to fine-tune the specifics of that DNS lookup. However, that is not what it does - it will use all name-resolving facilities on the system, which typically means it will do a hosts file lookup, and whatever else is configured in nsswitch.conf, which is usually DNS. For some of these non-DNS lookups, a source address binding may not make any sense, so it's not part of the least-common-denominator interface.
If you know that for your specific purpose you will never need the response of a name lookup from anywhere other than DNS, then you can use a DNS-specific function instead, one that will enable you to do this kind of fine-tuning.
There are several examples of DNS C libraries listed at gethostbyname dual network interfaces, select which one to use
The interface chosen to access a given IP address is dictated by the routing tables.
Since you presumably have the IP of the DNS server, it will be accessed by whatever interface the routing table says to use for that IP address, regardless of which application sends the request.
You would need to modify the routing table to force traffic over a particular interface. If it's only the DNS server that should use a fixed interface, you would add a route for that specific IP to the routing table for the interface you want.
On Linux, you can modify the routing table via the ip route command line tool.
rfc 3484 details an algorithm of which source addr (i.e. interface) to use when none is specified, but this works I think only for ipv6...
see /etc/gai.conf
Can someone possibly explain (within the size of a stackoverflow answer) the code required in order to emulate a network interface? I just know that there is virtualization software out there like Qemu that does this specific type of hardware emulation, but have no idea how this would work. Lots of books will show you how to create a program that listens on a TCP socket, but not create a host that gets its own IP address.
VirtualBox is open source. As a VM, with networking support, it should be sufficient to demonstrate to you what to do, along with a working implementation. https://www.virtualbox.org/wiki/Downloads
It's really depends what do you mean and what do you want to achieve. If you want emulate some real hardware you need via hypervisor's primitive emulate the most aspects mentioned in datasheet of corresponding adapter, if you want introduce some service, e.g. DNS or HTTP service visible in internal network: you need port teach some user land stack (e.g. LWIP or Slirp, or part if you need UDP only or lower) to communicate with hypervisor's internal network.
I'm using libpcap (and winpcap on Windows) in a C application to monitor network traffic. I need to differentiate between upload and download traffic on each network adapter, to produce connection speed stats, but the filter expressions used by the library don't seem to support this very easily (ie there are no 'incoming'/'outgoing' operators).
One approach that I have considered is to query the IP address of each adapter, and then use filters such as src host 1.2.3.4 (to measure uploads) and dst host 1.2.3.4 (to measure downloads).
My questions are:
Is there a better/simpler approach than the one above (something that would let me use the same filter expression for each adapter would be nice)?
If the above approach is the way to go, then is there any chance that a single adapter could have more than 1 IP address associated with it? The reason I ask is that the pcap_addr struct which holds the address details of a single adapter (in struct pcap_if) has a 'next' member suggesting that this is possible.
Firstly, remember, pcap sees only packets. It doesn't see "outgoing" or "incoming" - simply packets. So yes, you must filter using the src/dst in the ip headers. There is no other way to tell whether the packet is incoming or outgoing.
Secondly, yes, there is nothing stopping an adapter having multiple IP addresses. So you need to grab the IP addresses configured from that adapter. pcap_findalldevs() (WinPCap Documentation) ought to help you here, from which you should be able to deduce which devices you want to monitor.
Have you considered looking at pmacct - I have personally contributed to this in time past. This is a C tool that uses libpcap to passively monitor network traffic for accounting purposes.
Try tcpdump
•Managing Network Adapters Using GetAdaptersInfo
•Managing Interfaces Using GetInterfaceInfo
•Managing IP Addresses Using GetIpAddrTable
These are the three methods listed on the msdn IP Helper API. Why would I prefer one method over another?
They are mainly resulted from terminology differences, see http://msdn.microsoft.com/en-us/library/aa365798%28v=vs.85%29.aspx for the explanation regarding "adapter" and "interface". In short, an adapter is a data-link level abstraction while an interface being IP-level abstraction.
It will depend on the situation that you want to solve to determine what API to use. For example, link speed or tunnel type can only be acquired from adapters.