NetworkManager: I want to believe, but...

Alexandre Oliva aoliva at redhat.com
Tue May 27 03:39:33 UTC 2008


On May 23, 2008, "Colin Walters" <walters at verbum.org> wrote:

> On Thu, May 22, 2008 at 11:47 PM, Matthew Miller <mattdm at mattdm.org> wrote:
>> 
>> But "is the network up" a generally useful question?

> Yes.

> --Colin, who just finished last night implementing much improved
> network status handling in his SSH client via NetworkManager
> http://svn.gnome.org/viewvc/hotwire-ssh/trunk/hotssh/sshwindow.py?limit_changes=100&r1=4&r2=5&pathrev=5

So what does it do when one out of 3 networks a server is directly
connected to is down, and you attempt to connect to a host that is
reachable through one of the working interfaces?

How does "is the network up?" even being to make sense for anything
with more than one network interface?

What if two of the networks have redundant paths out to the Internet,
and the third doesn't, and only the third is up at a given moment?

And what if you're not trying to reach the Internet, just another
server down the hall that *is* reachable?

Heck, what if I'm just trying to reach one of the virtual machines
running on the local server, while the primary network interface was
taken off line?

What if I'm trying to diagnose a firewall problem on my server that
makes it *look* like the network is down for whatever heuristics
NetworkManager uses to make its decision, but that lets enough through
that I could get in from my desktop?  And vice-versa, except that I'm
not allowed to connect to my desktop because the network is allegedly
down.

How do you even begin to define 'network', to be able to decide what
the 'up' is about?


I don't doubt it's possible to make up a number of examples in which
the question actually makes sense and it has an answer that also makes
sense, but that's hardly enough to extend the claim from "useful for
some relevant cases" to "generally useful".  I think we're still quite
distant from the DWIM pipe dream.

-- 
Alexandre Oliva         http://www.lsd.ic.unicamp.br/~oliva/
Free Software Evangelist  oliva@{lsd.ic.unicamp.br, gnu.org}
FSFLA Board Member       ¡Sé Libre! => http://www.fsfla.org/
Red Hat Compiler Engineer   aoliva@{redhat.com, gcc.gnu.org}




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