programming with LIBNET

[rzcodeman]

Hello network programmers,
For a student project i'm going to use libnet to write a link dropper experimental tools which stands at gateway and drop the session which matchs against my filtering criteria. It is not kind of firewall but similar!

Who can give me a clue how can i jump into libnet programming.
by the way i download the source but there is a bit problems in compiling. i know it's my fault.
Cheers!

[NetRanger2007]

Using Libnet is simple and straightforward. The below piece of code put a single icmp hello on the wire:

char errbuf[LIBNET_ERRBUF_SIZE];

libnet_t *l; // Libnet context buffer. you always init at-least one of them in this library.
char *device = NULL; // In this case we select default network card to put in use
char *dst = "192.168.100.1"; // Suppose it is ip address of the server
char *src = "192.168.100.100";

u_long src_ip = 0, dst_ip = 0;
libnet_ptag_t t;
char *payload = NULL; // we have no payload
u_short payload_s = 0;



l = libnet_init(
LIBNET_RAW4, /* injection type */
device, /* network interface */
errbuf); /* errbuf */

dst_ip = libnet_name2addr4(l, pDst, LIBNET_RESOLVE); // Resolve dst ip address to a network byte ordered IPv4 address
src_ip = libnet_name2addr4(l, pSrc, LIBNET_RESOLVE);

t = libnet_build_icmpv4_echo(
ICMP_ECHO, /* type */
0, /* code */
0, /* checksum */
0x42, /* id */
0x42, /* sequence number */
NULL, /* payload */
0, /* payload size */
l, /* libnet handle */
0);

t = libnet_build_ipv4(
LIBNET_IPV4_H + LIBNET_ICMPV4_ECHO_H + payload_s, /* length */
0, /* TOS */
0x42, /* IP ID */
0, /* IP Frag */
64, /* TTL */
IPPROTO_ICMP, /* protocol */
0, /* checksum */
src_ip, /* source IP */
dst_ip, /* destination IP */
payload, /* payload */
payload_s, /* payload size */
l, /* libnet handle */
0);


libnet_write(l); // put the packet on the wire
libnet_destroy(l); // destroy the context buffer

Meanwhile for a whole tutorial search the web or visit here:
network programming with libnet

[NetRanger2007]

For resources regarding to network security and so on take a look at the following blogspots:
low level network programming
and
network security vulnerabilities and exploits

[mamehmood]

Hi All
I am using Libnet.
Can any one help me with IP Fragmentation? Which value should i use so my packet get fragmneted? can you quote any exmpale of Payload and IP Frag flag value?
Regards
Aamir