Re: artificial latency for a network interface

[Andrew Morton <andrewm@uow.edu.au>]

Andreas Schuldei wrote:
> 
> to simulate a sattelite link, I need to add a latency to a
> network connection.
> 
> What is the easiest and best way to do that?
> 
> I wanted to do that using two tun devices.
> I had hoped to have a routing like this:
> 
>  <-> eth0 <-> tun0 <-> userspace, waiting queue <-> tun1 <-> eth1

yes, that works very well.  A userspace app sits on top of the
tun/tap device and pulls out packets, delays them and reinjects
them.

The problem is routing: when you send the packet back to the
kernel, it sends it straight back to you.  You need to rewrite
the headers, which is a pain.

A simpler approach is to use policy routing - use the source
and destination devices to override the IP addresses.  Works
well.  The code is at

	http://www.uow.edu.au/~andrewm/packet-delay.tar.gz

It has its own variable bandwidth management as well
as variable latency.  It's for simulating narrowband, high
latency connections.