From owner-freebsd-hackers@FreeBSD.ORG  Wed Jul 31 19:47:04 2013
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Date: Wed, 31 Jul 2013 23:47:02 +0400
Message-ID: <CAE-mSOJZ4OwpPhjmkJwEOjuHXGjtH5LHLJ+92qexjQs6EgPM-g@mail.gmail.com>
Subject: Re: Stacking lots of IP's on a single box - any 'gotchas'?
From: Sergey Kandaurov <pluknet@gmail.com>
To: Karl Pielorz <kpielorz_lst@tdx.co.uk>
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On 31 July 2013 13:37, Karl Pielorz <kpielorz_lst@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.

> 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