Weird networking problem

Jason Shein jason-gaRZxGPHtpBxZtjKW1aY+1aTQe2KTcn/ at
Sun Jul 11 19:34:22 UTC 2004

This list is more up to date

On Sun, 2004-07-11 at 15:28, Jason Shein wrote:
> Try using an anonymous proxy ( )
> and see if you can access the inaccessible sites. If you can, your IP is
> somehow blocked somewhere. If you still can't, then the problem is not
> with your IP
> On Sun, 2004-07-11 at 02:32, Marcus Brubaker wrote:
> > Alright, I have a strange problem that I've been up against for the past
> > two or three days and am running out of ideas so I figured I'd post here
> > and see if anyone could help.  About 3 days ago my DSL connection seemed
> > to stop working.  Further analysis showed that the connection was still
> > there but certain sites/servers were inaccessible.  For instance I was
> > able to load but was unable to load  Similarly for
> > many other sites, including an inability to get to my own ISPs website. 
> > It wasn't simply restricted to http access either as ssh, pings and
> > traceroutes showed similar behaviour.  Neither was there a browser issue
> > (tried Mozilla, wget, IE, etc).
> > 
> > Thinking it might be an issue with my firewall I replaced the firewall
> > with a spare.  This failed to make any difference.  Thinking perhaps it
> > was a modem issue I also swapped modems again to no avail.  Finally I
> > called the ISP and, at their urging, I directly connected a Windows XP
> > laptop to the modem to make their tech support people feel more at
> > ease.  As expected, this made no difference  They ran line tests and
> > checked network status.  I was informed that Bell had no issues, they
> > had no issues and, in fact, by everything they could tell, I had a
> > picture perfect, low-noise DSL line which was connecting and
> > authenticating wonderfully.
> > 
> > And the strangest part of the whole thing is how erratic it is in what
> > hosts it can connect to and what hosts it can't.  For instance, there
> > are two hosts on the U of T CS network that I have access to.  They are
> > separated by very little (practically next to each other) and share the
> > same route out of the U of T networks.  Against all intuition and odds,
> > one of them is perfectly accessible while the other isn't.  However,
> > from my machine at home on Rogers both machines are readily accessible
> > 
> > Now, about the only two things that I can think to be a problem is that
> > either a) something very unusual is going on with my ISPs routers or b)
> > the IP address has somehow been blacklisted somewhere.  Now, I can't
> > imagine why b) would be the case and, even if the server was blocked as
> > a spam relay (which, AFAIK it isn't, and yes I've checked), those
> > usually block at the mailer level, not the IP level, right?  While I was
> > able to try a different IP address with my ISP (which worked great) it
> > doesn't rule out option a) since the address was on a completely
> > different subnet.
> > 
> > My own feeling is that it is option a) but at the moment I have no way
> > to show that.  I spent two hours on the phone today convincing the
> > bloody tech support person that it was *not* a software configuration
> > issue and he refused to believe that anything could be wrong with their
> > system that he was unaware of.  Unfortunately, I don't know of any way
> > to test or determine where the problem is since traceroute has been
> > inconclusive at best and I'm not a networking expert.
> > 
> > So I guess my question is this: what could I try/test in order to either
> > rule out or support option a) or b)?  Should I just call back the ISP
> > and insist that a ticket be filed with their real networking people?  If
> > that is the case, does anyone have any theory on what might cause such
> > unusual behaviour so that I can make a better case?  Any other advice?
> > 
> > Thanks to everyone (especially for reading this far!) for any help or
> > even positive thoughts.  I'm about ready to put my head through the wall
> > on this one.
> > 
> > Regards,
> --
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The Toronto Linux Users Group.      Meetings:
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