[ntp:questions] ntpdate.c unsafe buffer write

David L. Mills mills at udel.edu
Wed Feb 13 04:45:29 UTC 2008


Depends who the clients are. An ntpd client will not come up in the 
first second, although successive associations will come up at 2-s 
intervals. I would not expect 2000 clients to come up at the same exact 
time anyway due ordinary latency variations in the boot process. I would 
be more worried about a broacast server coming up with 2000 corporate 
broadcast clients, but in that case the initial client response is 
randomized over the poll interval.


Unruh wrote:

> Martin Burnicki <martin.burnicki at meinberg.de> writes:
>>David L. Mills wrote:
>>>The behavior after a step is deliberate. The iburst volley after a step
>>>  is delayed a random fraction of the poll interval to avoid implosion
>>>at a busy server. An additional delay may be enforced to avoid violating
>>>the headway restrictions. This is not to protect your applications; it
>>>is to protect the server.
>>Is it really necessary to insert a random delay after a step? There has
>>already been a random delay immediately after startup, before the client
>>has decided that a step was required.
>>So even if a bunch of clients started up at the same time and had to step,
>>they wouln't step at the same time, and thus wouldn't do the next iburst
>>volley at the same time anyway.
> Why not? The power comes on on your computer farm of 2000 machines, all the clients are the same type so the
> bootup sequence is identical. They all start ntp at the same time, to
> within a second or so. And suddenly the poor server is flooded. 
>>Martin Burnicki
>>Meinberg Funkuhren
>>Bad Pyrmont

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