netdev - Re: RFC Hanging clean-up of a namespace

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Date:	Thu, 19 Jan 2012 22:03:52 +0100
From:	David Lamparter <equinox@...c24.net>
To:	David Miller <davem@...emloft.net>
Cc:	equinox@...c24.net, hans.schillstrom@...csson.com,
	netdev@...r.kernel.org, ebiederm@...ssion.com
Subject: Re: RFC Hanging clean-up of a namespace

On Thu, Jan 19, 2012 at 03:27:52PM -0500, David Miller wrote:
> From: David Lamparter <equinox@...c24.net>
> > On Thu, Jan 19, 2012 at 02:31:05PM -0500, David Miller wrote:
> >> Then if a new netns is created that tries to reuse the address used by
> >> the mini-netns which hasn't cleared yet, you give -EAGAIN until all
> >> the timewaits expire.
> > 
> > The effect of this is that you end up being unable to reboot lxc based
> > virtualised hosts without waiting 2 minutes for the TCP timers to
> > expire. That sounds completely unacceptable to me.
> 
> All you are saying to me is that we are on a trajectory to major problems
> if it becomes pervasive that time-wait gets cancelled out and addresses
> then get reused so quickly.

On the funny side, RFC 793 page 28 actually states under "Knowing When
to Keep Quiet" that
  "To be sure that a TCP does not create a segment that carries a
  sequence number which may be duplicated by an old segment remaining in
  the network, the TCP must keep quiet for a maximum segment lifetime
  (MSL) before assigning any sequence numbers upon starting up or
  recovering from a crash in which memory of sequence numbers in use was
  lost. For this specification the MSL is taken to be 2 minutes."

Let's implement that, I bet people will love a 2 minute wait on TCP
connections after booting :-)


-David
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