Messages in this thread | | | From | "David Schwartz" <> | Subject | RE: TCP keepalive seems to send to only one port | Date | Mon, 25 Dec 2000 16:33:07 -0800 |
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> On Sat, Dec 23, 2000 at 04:19:31PM -0800, David Schwartz wrote:
> > > This means that keepalive is useless for keeping alive more than > > > one connection > > > to a given host.
> > Actually, keepalive is useless for keeping connections > > alive anyway. It's > > very badly named. It's purpose is to detect dead peers, not keep peers > > alive. > > Then what do you do when you are behind a NAT?
If the administrator of the NAT meant for you to have a permanent mapping, she would have put one there. Using keepalives to hold a NAT entry open indefinitely without activity would be considered abuse in most NAT configurations. The NAT might not consider a keepalive to be activity anyway (arguably, it shouldn't).
> And how do you > expire entries in > ESTABLISHED state that could stay lingering forever without some sort of > keepalive? (The FINs might have been lost due to a conectivity > transient, so > you can have another perfectly valid and alive connection with > the same host, > and application-level timeouts are useless for some applications > (*cough*nc*cough*))
I don't understand this argument. First you demonstrate the need for application-level timeouts, then you say application-level timeouts are useless. Actually, your first argument is correct, protocols layered on top of TCP that don't provide for timeouts are defective.
DS
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