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Re: [lwip-users] Handling sudden disappearance of network i/f

From: Kieran Mansley
Subject: Re: [lwip-users] Handling sudden disappearance of network i/f
Date: Thu, 21 Sep 2006 08:49:30 +0100

On Wed, 2006-09-20 at 23:51 +0100, Clive Wilson wrote:
> If the serial link 
> that LwIP's PPP layer depends upon suddenly disappears, then on this event 
> I call pppSigHUP to inform PPP of the low-level link's absence. This in 
> turn calls netif_remove as you mention. However, if a socket call such as 
> read(), write() etc is made after the serial link dies, I don't see these 
> calls returning with an error to indicate a timeout waiting for response. 

OK, I understand your problem better now, but I'm afraid I'm not 100%
sure what the correct behaviour is in this case either.  I just tried it
with linux by establishing an ssh connection across an ethernet
interface, then taking that interface down.  The connection didn't
immediately terminate, and when I brought the interface back up, the
connection resumed where it had left off - the data I had tried to send
while the interface was down was then sent.

I think the connection would eventually time out (once the right number
of retransmission timeouts had passed without it getting a response, it
would give up).  

So, looks like lwIP is doing approximately the right thing.  Socket
calls aren't made aware that the physical network has gone away.


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