6.x, 4.x ipfw/dummynet pf/altq - network performance issues

Justin Robertson justin at sk1llz.net
Thu Feb 15 23:06:27 UTC 2007

  This is definitely worst-case, it's simulating a DDoS attack at the 
network. What is really surprising is that just 1mbps of traffic is able 
to kill a 6.x box doing routing. If it were, say, 600mbps that I'd 
understand as you're pushing over a million PPS. But 1mbps? :-\

Freddie Cash wrote:
> On Thursday 15 February 2007 01:29 pm, Justin Robertson wrote:
>>     Send a flood of 60 byte syn packets with the tcp sack option thru
>> it and check out what happens. It's pretty weird and I can't explain
>> why. If you block the packets on the box via ipfw it's fine, the second
>> it has to make a routing decision everything goes out the window, it
>> seems. There's 100% packet loss on all protocols. I'm not using NAT,
>> there are real IPs in different C classes on the other side of the box.
> Is that something that would occur normally?  Or is this a 
> worst-case/stress-test trying to break things?  How are you generating 
> the packets?
> I'm not a network guru, and haven't done much in the way of 
> network-related stress-testing, but I'm always looking for ways to do so.


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