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Random Packet Generator
-----------------------
randpkt is a small utility creates a libpcap trace file full of random packets.
You can control the number of packets, the maximum size of each packet,
and the type of each packet. It is not build by default, but you
can create it in the top-level Wireshark directory by typing:
make randpkt
By creating many randomized packets of a certain type, you can
test packet sniffers to see how well they handle malformed packets.
The sniffer can never trust the data that it sees in the packet because
you can always sniff a very bad packet that conforms to no standard.
Randpkt produces __very bad__ packets.
When creating packets of a certain type, randpkt uses a sample
packet that is stored internally to randpkt. It uses this as the
starting point for your random packets, and then adds extra random
bytes to the end of this sample packet.
For example, if you choose to create random ARP packets, randpkt
will create a packet which contains a predetermined Ethernet II header,
with the Type field set to ARP. After the Ethernet II header, it will
put a random number of bytes with random values.
Run 'randpkt' with no options to see the usage statement. As of the
writing of this text, the usage is:
Usage: randpkt [-b maxbytes] [-c count] [-t type] filename
The usage statement produced by randpkt will list the legal types.
If you choose a maxbytes value that is less than the size of the
sample packet, then your packets would contain only the sample
packet... not much variance there! Randpkt exits on that condition.
To add a new packet type to randpkt, you must add information
in the following locations.
1) Add the packet type name to the enum of produceable packets:
/* Types of produceable packets */
enum {
PKT_ARP,
PKT_ETHERNET,
PKT_FDDI,
PKT_LLC,
PKT_TR
};
2) Type in the bytes from your sample packet
/* Ethernet, indicating ARP */
uint8_t pkt_arp[] = {
0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0x00, 0x00,
0x32, 0x25, 0x0f, 0xff,
0x08, 0x06
};
3) Add a record to the 'examples' array. The fields are
1. Abbreviation (for use in '-t' command line argument)
2. Full name (for use in usage statement)
3. Enum type
4. Array holding sample packet
5. Wiretap encapsulation type of datalink layer in your
sample packet
6. Length of sample packet. Use the handy array_length()
macro to avoid counting the bytes yourself.
pkt_example examples[] = {
{ "arp",
"Address Resolution Protocol",
PKT_ARP,
pkt_arp,
WTAP_ENCAP_ETHERNET,
array_length(pkt_arp) },
{ "eth",
"Ethernet",
PKT_ETHERNET,
NULL,
WTAP_ENCAP_ETHERNET,
0 },
};
Note that packets that designate only their datalink type have no sample
arrays, since the only thing that needs to be set is the datalink type,
which is a field in the libpcap frame record; it's not a part of the
packet itself.
Enjoy!
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