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

[Kieran Mansley]

On Mon, 2006-09-18 at 13:00 +0100, address@hidden wrote:
> Hello,
> 
> I have a problem whereby if the low-level comms supporting a network
> interface I'm using for LwIP suddenly (and unexpectedly) disappears,
> the upper stack layers don't seem to be becoming aware of this. I'm
> using the PPP network interface, but I don't think that should make
> any difference to the question in principle.
> 
> I am able to determine when the data channel goes down (via a
> callback), so can anyone say if there is a variable or data member in
> the upper layers that I should be modifiying on this event, to
> indicate that there is no longer a means of tx'ing/rx'ing packets?
> Perhaps the variable is actually in the network layer (PPP in this
> instance)? 

Are you hoping to notify the application, or TCP/IP layers?  TCP/IP
would do very little with this information as it tries to be resilient
across temporary network outages.  E.g. if you unplug an ethernet cable,
then plug it back in again after a few seconds, the TCP connections will
all still be there.  There are timer mechanisms that try to notice if a
link has gone away for longer than you're willing to wait (in order that
the connection gets closed locally and so frees resources).

If the physical layer has really gone away for good, I think the
appropriate action would be to unconfigure the network interface, using
netif_remove() (I think - haven't checked the source).

Kieran