[Sugar-devel] [DESIGN] Reflect internet connectivity in the 'Network' frame icon

[Samuel Greenfeld]

There also is the possibility of a false positive if we check too
little.   Some networks might like to act like everything is available
when that is not the case.

Captive portals such as those seemingly found at pretty much every
university and hotel I've gone to lately come to mind, and these may
vary in their approaches.


On 02/16/11 04:53, Sascha Silbe wrote:
> Excerpts from Martin Langhoff's message of Tue Feb 15 14:57:01 +0100 2011:
> 
>> Going back to your original post to note something important: these
>> statuses aren't important _just_ to show in the UI. This should be a
>> system status property that can be queried by activities and by
>> cronjobs / cli utils.
> 
> Please be very careful with this. If your sensor incorrectly detects
> that no internet connection is available, everything that relies on it
> will break. Even just checking the NetworkManager status without a way
> for the user to override it is a bad idea since NetworkManager might not
> have a complete idea of what's going on [1,2].
> 
> When trying to check availability of "the internet", you are bound to
> get false positives. The server(s) you ping in your sensor might be
> down even though the server you are going to connect is still be 
> reachable. The IPv4 default route might be down, but there might still
> be a way to reach the target (IPv6, proxy, ...).
> 
> Unless there's a large application-level cost associated to it, it
> might be a better idea to just try establishing the connection. A
> SYN packet is as cheap as an ICMP echo request and you'll know for
> sure whether the exact server you're trying to reach is available or
> not.
> 
> The "internet" sensor might be useful to monitor changes and trigger
> connection attempts, though. If you use exponential back-off, you could
> reset the retry timer whenever the sensor switches from "offline" to
> "online".
> 
> Sascha
> 
> [1] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=511439#35
> [2] https://bugzilla.gnome.org/show_bug.cgi?id=418745
> 
> 
> 
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