Thread: IP blocking or MAC address blocking
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Re: IP blocking or MAC address blocking

 
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  #7
Dec 22nd, 2008
Saying that 'XXX is not possible in Java' is pretty misleading IMO.

Is I/O and Networking possible in Java? You might say yes, there are packages like java.io.* and java.net.* for it. But is it really possible in *java*? Both I/O and Networking libraries which are part of the standard libraries at their core make JNI calls and are platform specific since the way I/O is performed is OS/platform specific. So as long as you have the proper JNI code in place along with dynamic libraries for your target platforms, almost anything is possible in Java. The same argument applies to 'Java only works at Application/Transport layer'.

But to answer the question, yes, a ping utiilty can't be written using the standard Java libraries, since AFAIK, Java doesn't allow creation of raw sockets which are needed to send ICMP packets.
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Ping requires ICMP packets. These packets can only be created via a socket of the SOCK_RAW type. Currently, Java only allows SOCK_STREAM (TCP) and SOCK_DGRAM (UDP) sockets. It seems unlikely that this will be added very soon, since many Unix versions only allow SOCK_RAW sockets to be created by root, and winsock does not address ICMP packets (win32 includes an unsupported and undocumented ICMP.DLL).
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