Re: Telnet: route to host
From: Brian K. White (brian_at_aljex.com)
Date: 08/04/05
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Date: 3 Aug 2005 22:48:35 -0400
> Why does the SCO box come up with the bogus error message?
As Bela pointed out it turns out it's not bogus, or at least it's not the
sco box being bogus.
First consider a "normal" case.
Suppose the destination box was several hops away on the internet.
Suppose you have a correct routing table on your sco box that says the route
to that ip lies via your gateway router.
Suppose the gatway router also has a correct routing table that points to
one of your isp's machines.
Suppose that isp machine is misconfigured and has no route anywhere in it's
routing table that matches the IP you tried to reach? (meaning, no default
route either of course)
The traffic left your box correctly and there is nothing you can fix on your
box, but due to botched routing in one or more machines outside of your
control, it hit a dead end.
The last machine in that dead end, the machine that received the traffic but
doesn't know what to do with it, _says so_ back to the machine it got the
traffic from and the various machines relay that "no route to host" message
back ultimately to you the originator.
The point: The no route message doesn't come from the originating box, it
comes from whichever machine was given a task it doesn't know how to do. If
your own routing table is incorrect, that's the only time your own box
generates the error.
In your case, your routing table is correct enough to get you to the correct
next hop along the way to the destination.
That next hop happens to also BE the destination but that doesn't change
much.
The machine you reached claims it doesnt' know how to route traffic to the
ip you asked for.
That's basically a flat lie.
If your destination was an IP (lets leave possible wrinkles with hostnames
out for the moment), and if the linux box nic was that same IP, and if you
physically reached that nic, then techincally the linux box is lying when it
says no route to host.
There are other types of errors besides no route so it is still generally
correct that your box shows you errors it gets from the next hop, even in
this case whre the next hop is the destination.
Perhaps the sco box should be smart enough to know that a same-subnet route
is a special case and that there can be no such thing as that particular
error in that particular case, and throw away the error message it got from
linux and instead report something like "Host is claiming no route to host.
Host, whom I supposedly can't reach, told me this, over the route that
supposedly doesn't exist. Maybe host has pms. I give up." :)
Perhaps the linux box should be more honest and say "denied by firewall
rules". That sounds like painting a big target on onesself saying "locked
door here--->" which is counter to the goals of a firewall, but it's
unavoidable anyways. No matter what the linux box wants to say, the
physically next hop box always has the ability to know it's a lie, and it's
possible for new machines that are hip to this trick and report the truth
back to the originator to populate the internet over time. And any box
anywhere already always has the ability to know it's a lie if they can reach
the box by any other means. So it's a cute but ultimately pointless trick.
This kind of thing bugs me because it inflicts wasted time damage on people
like you & me who may think there really is a routing problem and chase our
tails trying to fix what isn't broken.
I think things like error messages shoudl be sacrosanct. You don't spoof
them. Start doing that and error messages become a useless diagnostic tool,
and THEN where are we?
Shortsighted idiot linux developers are destroying the world.
Brian K. White -- brian@aljex.com -- http://www.aljex.com/bkw/
+++++[>+++[>+++++>+++++++<<-]<-]>>+.>.+++++.+++++++.-.[>+<---]>++.
filePro BBx Linux SCO FreeBSD #callahans Satriani Filk!
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