Stacking lots of IP's on a single box - any 'gotchas'?

[Julian Elischer]

On 8/1/13 4:27 AM, Diane Bruce wrote:
> On Wed, Jul 31, 2013 at 11:47:02PM +0400, Sergey Kandaurov wrote:
>> On 31 July 2013 13:37, Karl Pielorz <kpielorz_lst at tdx.co.uk> wrote:
>>> Hi,
>>>
>>> We've got a number of boxes we'd like to consolidate - this could mean
>>> upward of 1,500 IP's on a single box (9.1 amd64).
>>>
>>> Last time we did anything like this we hit at issue at around 900 (ntpd
>>> 'binds' by default to all available IP's - I think we had a workaround for
>>> that).
>>>
>> This is because select() has a limit on FD_SETSIZE (1024).
>> If it tries to select > 1024 fds, bad things could happen.
>> Newer ntpd (not in base) has a feature to bind only to the specific
>> interface; this was used to run ntpd on boxes with > 1200 IPs on 1 i/face.
> I can tell you from experience that FreeBSD has no problems at all selecting
> on more than 1024 fds. In fact, this is what I would suggest you do.
> Your limit then is going to be the number of anonymous ports on each
> IP. Figure 32000 or so to be conservative that's more than what you need.
Once again. I ask: Why do you want to do this?

if you just want to respond to a small number of ports on multiple 
addresses there are easier ways to do this with a single socket.



>
>   
>>> But is there any hard limit we're likely to encounter putting so many IP's
>>> on a single machine? - Are there any limits that would likely need tuning to
>>> support that many IP's?
>>>
>> Unlikely, besides those unrelated things like ntpd+select() et.al.
>>
>> -- 
>> wbr,
>> pluknet
> - Diane