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Re: [hybi] NAT reset recovery? Was: Extensibility mechanisms?

Dave Cridland <dave@cridland.net> Tue, 20 April 2010 13:32 UTC

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Date: Tue, 20 Apr 2010 14:32:27 +0100
From: Dave Cridland <dave@cridland.net>
To: "Markus.Isomaki@nokia.com" <Markus.Isomaki@nokia.com>, Server-Initiated HTTP <hybi@ietf.org>, "Thomson, Martin" <Martin.Thomson@andrew.com>, Pieter Hintjens <ph@imatix.com>, Jamie Lokier <jamie@shareable.org>
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Subject: Re: [hybi] NAT reset recovery? Was: Extensibility mechanisms?
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On Tue Apr 20 13:42:47 2010, Markus.Isomaki@nokia.com wrote:
> Dave Cridland wrote:
> >
> >Note that in IMAP, there are technically no actual keepalives,
> >but servers can send an ignorable
> >"* OK", and in extreme cases, can fake a delivery to cause a
> >client to do something. Clients have a NOOP command. I suspect
> >a lot of the issues with IMAP relate to there being no simple
> >way for the server to ping the client built-in to the protocol.
> >
> 
> Yes, this "* OK" is what I have seen. I agree that the lack of an  
> explicit in-built mechanism is an issue and we should learn from  
> that for WebSocket.
> 
> 
What you'll also see on some IMAP servers is a "* EXISTS"/"* EXPUNGE"  
sequence sent at about the 29th minute of a client in IDLE mode, as  
that turns out to be the only way to "wake" some clients and check if  
they're there. This is a hideous hack, but the thing is that it's now  
too late (by 20 years) to mandate a server-initiated NOOP.


> >Having the server send a SP on an idle session is
> >useful for defeating NAT timeouts,
> 
> Here I'd really prefer the client to do it, as it should know  
> better. And the host can potentially optimize between different  
> connections etc.
> 
> 
I'm open to suggestions. If the server sends a simple keepalive only  
on silent connections on a reasonably lengthy interval, this seems to  
be to cover most options - it in effect means that clients can do it  
sooner if they wish.


> >whereas the ping
> >(XEP-0199) is extremely useful to definitively check reachability.
> >
> 
> Is that being used today by servers?
> 
> 
Absolutely, if you connect an XMPP client to jabber.org and leave it  
idle and silent, the server will eventually wonder if you're still  
there and ping you (it'll take about 5-7 minutes). Other servers may  
well do similar things.

Dave.
-- 
Dave Cridland - mailto:dave@cridland.net - xmpp:dwd@dave.cridland.net
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