Dear all,
I'd like to enhance the JICMP library in a manner that you can also set the
packet size.
This is very important on MPLS network where the mtu size is fixed and can be
tested using ping.
Just taken a look at the code and it seems that actually we have a 56 byte
fixed size packet.
Here is the relevant code in ICMPEchoPacket
/**
* Unique named padding that is placed in front of the incremental padding.
*/
private static final byte NAMED_PAD[] = { (byte) 'O', (byte) 'p', (byte)
'e', (byte) 'n', (byte) 'N', (byte) 'M', (byte) 'S', (byte) '!' };
/**
* Timestamp when packet was sent
*/
private long m_sent;
/**
* Timestamp of when packet was received.
*/
private long m_recv;
/**
* The thread id of the sender. Effective key for the packet.
*/
private long m_tid; // thread id
/**
* Padding used to make the packet conform to the defacto unix ping program
* (56 bytes).
*/
private byte[] m_pad;
/**
* The ping rtt (microseconds)
*/
private long m_rtt;
/**
* This is the amount of padding required to make the ICMP echo request 56
* bytes in length. This is just following the available code for ping ;)
*/
private static final int PAD_SIZE = 16;
And when you construct the packet....
/**
* Creates a new discovery ping packet that can be sent to a remote protocol
* stack. The ICMP type is set to an Echo Request. The next sequence in the
* ICMPHeader base class is set and the sent time is set to the current
* time.
*
* @param tid
* The thread id for the packet.
*
* @see java.lang.System#currentTimeMillis
*/
public ICMPEchoPacket(long tid) {
super(ICMPHeader.TYPE_ECHO_REQUEST, (byte) 0);
setNextSequenceId();
m_rtt = 0;
m_sent = 0;
m_recv = 0;
m_tid = tid;
m_pad = new byte[PAD_SIZE];
for (int x = 0; x < NAMED_PAD.length && x < PAD_SIZE; x++)
m_pad[x] = NAMED_PAD[x];
for (int x = NAMED_PAD.length; x < PAD_SIZE; x++)
m_pad[x] = (byte) x;
}
Now if we add a new constructor we can also set the pad_size so that we can set
the packet size:
public ICMPEchoPacket(long tid, int pad_size) {
super(ICMPHeader.TYPE_ECHO_REQUEST, (byte) 0);
setNextSequenceId();
m_rtt = 0;
m_sent = 0;
m_recv = 0;
m_tid = tid;
m_pad = new byte[pad_size];
for (int x = 0; x < NAMED_PAD.length && x < pad_size; x++)
m_pad[x] = NAMED_PAD[x];
for (int x = NAMED_PAD.length; x < pad_size; x++)
m_pad[x] = (byte) x;
}
We can have packet of any size.
We can just add t MAX_PAD_SIZE to prevent creating arbitrary size ICMP row
packets.
Any suggestion?
Antonio
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