Re: Blocking N consecutive packets with netgraph

benjamin@xxxxxxxxxx wrote:

I need to test a multicast streaming media application by selectively
dropping packets in the network connecting the source to the viewer.

The capability I need is to drop N consecutive packets, where N ranges
from 1 to 50 and is chosen via the command line.

I had hoped to do this with dummynet and ipfw, but apparently I can
only drop packets with a specified probablity. The network topology
for this method was to bridge two ethernet nics, then use dummynet pipes
to vary the bandwith and packet loss rate.

I also tested a method using ipfw to temporarily enable packet block
rules using a short sleep interval, but there was only very coarse
control of the number of packets blocked.

Is it feasible to do this with netgraph? Please outline how this may
be accomplihsed.



Certainly it is as long as you are happy to write your own node.
Now, don't be scared.. nodes are relatively simple to write.

They can be loaded dynamically once written.
check out all the nodes available at:
http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/netgraph/
you can start easily with the "sample" node.

change its name and compile it by adding a directory in the /sys/modules.netgraph directory,
copying the Makefile from another one and modifying it accordingly.

start hacking..

documantation is in:
http://www.freebsd.org/cgi/man.cgi?query=netgraph&apropos=0&sektion=4&manpath=FreeBSD+7.0-current&format=html

and all the other man pages for netgraph modules,


TIA

Tom Benjamin
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