Next
Previous
Contents
After you intercept a packet, it is possible to change its header or contents
before reinjecting it back. Here are a few rules you might need to keep in mind:
- IP header checksum is always recalculated on injection
- IP ID field is filled in for you if you leave it 0.
- The length of the packet is updated for you.
All other parts of the IP header can be modified and its up to you to insure their
sanity.
It is not necessary to intercept a packet in order to inject it. You can form
your own packets and inject them into an open and bound divert socket. The
header rules from above apply.
In addition, you need to pass to the divert socket a sockaddr_in structure
(see example program), which will tell the socket where to inject. If you
leave the structure 0-ed out or pass a NULL - the divert socket will attempt
to inject the packet in the outbound direction (on the wire). If instead
you fill the sockaddr_in structure with the address of one of the local interfaces,
the divert socket will attempt to inject the packet inbound, as if it came from
that interface. All addresses, of course, should be in network byte order.
Injection of packets that look like they are being forwarded by your host
must include an address of the incoming interface (actually - any valid interface
address will probably work).
As of this reading, the divert sockets do not handle the defragmentation and
fragmentation of diverted packets - you always get the fragments as they are on
the wire and you should not inject fragments larger than PMTU. It is anticipated
that the fragmentation/defragmentation capability will be added in the near future.
Next
Previous
Contents
| 
Free eBook: 
