[K12OSN] Tuning LTSP Performance

[Terrell Prude' Jr.]

Rob Owens wrote:
> On Fri, Aug 29, 2008 at 11:41:42PM -0400, Terrell Prude' Jr. wrote:
>   
>> Robert Arkiletian wrote:
>>     
>>> 2008/8/29 Terrell Prude' Jr. <microman at cmosnetworks.com>:
>>>  
>>>       
>>>> 2.)  If you're running LTSP of any sort, it's assumed that you're running,
>>>> at a minimum, a switched 10/100 environment (if not, then you really 
>>>> should
>>>> be!).  Unless A.) it's a managed switch capable of port mirroring, and B.)
>>>> you control said switch, you can sniff *your* traffic, but not other
>>>> peoples.  To keep the Les Mikesells of the world happy, I'll point out 
>>>> that
>>>> yes, you could sniff the server if it's physically accessible.  But in 
>>>> God's
>>>> name, I hope you have it secured physically so's to (largely) prevent 
>>>> that!
>>>>    
>>>>         
>>> Please enlighten me Terrell. I don't understand how having access to
>>> the server is a vulnerability in terms of sniffing packets. One must
>>> have root access to be able to use a program like tcpdump or wireshark
>>> to capture packets. So if they don't have root how can they sniff?
>>>  
>>>       
>> Easy.  Say you're a "curious" kid.  :-)  Just insert your own switch 
>> (yes, they're available on eBay) in between the server and its network 
>> drop.  On your switch, mirror the port to your laptop (laptop HD's are 
>> pretty big nowadays).  Boom, you've done it, and no, it ain't that hard 
>> to do.  I do this sort of thing regularly at work as part of my network 
>> engineer duties when troubleshooting certain problems.
>>
>>     
>
> Or even easier (well, at least cheaper) is to throw a hub in between the server and the main switch.  A hub mirrors all ports -- at least that's how I understand it.  Anyway, I've tried it and it works.
>
> -Rob
>
>   

Yep, that'll certainly do it, too.  The problem with that approach is 
that it'd be much more noticeable from a performance standpoint.  
Collisions will slow down LTSP to a crawl, and further, you'll slow the 
server's NIC down to 100Mbps (Gig-E switches don't exist--fortunately).  
Therefore, naturally, someone'll investigate sooner than if you used a 
managed 10/100/1000 switch to do the same thing.

--TP