[Vm-dev] Re: Unix VM listen behavior?

Andreas Raab andreas.raab at gmx.de
Wed Jan 14 09:23:18 UTC 2009

Bert Freudenberg wrote:
> On 14.01.2009, at 07:38, Andreas Raab wrote:
>> Hi Folks -
>> I have a quick question about the expected behavior of the Unix VM 
>> when running on a machine with multiple IP addresses. We have a box 
>> with two interfaces (eth0 and eth1 respectively) and only eth0 was 
>> originally enabled. Listening without specifying an interface worked 
>> fine for clients connecting to the (static) IP configured for eth0.
>> Then, we enabled eth1 and gave it its own (static) IP address. We had 
>> two images running, one without specifying the interface, one 
>> specifying the IP for eth1 (both images had been restarted after the 
>> change was made). The result was that clients could connect to the 
>> image running on eth1 but not to the one running on eth0. Only when we 
>> changed that image to use the explicit IP address configured for eth0 
>> everything worked as expected (i.e., clients could connect to either 
>> IP address).
>> Question: Is this the expected behavior? I'm not sure if not 
>> specifying the interface implies that the VM accepts connections on 
>> all interfaces, or only the first one, the last one, a random one or 
>> not at all. Any insights are greatly appreciated - we have a working 
>> setup but it would be nice to know whether this is what we should 
>> expect to see or not.
> Well, I would expect it to listen on all interfaces.
> What does netstat say (or lsof)?

I'll have to check. This happened in an emergency (DDOS on our shiny new 
data center which wasted more bandwidth than I could previously imagine) 
and I couldn't spend much time on investigating the details. If things 
are quiet tomorrow I can run a few tests. But it is useful to know that 
the expected behavior is that it should be listening on all interfaces.

Lesson of the day: Big pipes are no replacement for a fallback system on 
the other end of the world with all your data replicated on it. Well, 
lesson learned :-(

   - Andreas

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