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why "no route to host" when it can be pinged?

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From: Bela Lubkin <filbo@armory.com>
Subject: Re: Telnet: route to host
Date: 3 Aug 2005 17:25:01 -0400
Message-ID: <200508031424.aa20774@deepthought.armory.com> 
References: <20050803131820.A17532@egps.egps.com>
<200508031246.aa22159@deepthought.armory.com>
<20050803164313.B25182@egps.egps.com> 

Nachman Yaakov Ziskind wrote:

> Bela Lubkin wrote (on Wed, Aug 03, 2005 at 03:46:25PM -0400):
> > Nachman Yaakov Ziskind wrote:
> > > 
> > > What gets me is when I connect to a non-functioning port, I get:
> > > 
> > > $ telnet 10.1.1.4 5555
> > > Trying 10.1.1.4...
> > > telnet: Unable to connect to remote host: No route to host
> 
> > It's probably running an internal firewall which is set to generate ICMP
> > host unreachable responses on attempts to access blocked ports.  It's
> > like the voice saying "nobody in here but us chickens", except computers
> > are much more likely to take such a response literally...
> 
> I found the telnet problem (I had to insert an IPTABLES rule). But that 
> wasn't my question, so I'll restate it:
> 
> Why does the OpenServer box generate a 'no route to host' error in a 
> case like this? It should either wait and time out, or return 
> 'connection refused'.

What was the generic IPTABLES rule you were overriding?  I'm guessing
something like:

  all ports not otherwise covered:
    reject with "ICMP destination unreachable: host unreachable" 

to which you added:

  TCP port 23 [telnet]:
    accept

The message isn't bogus if the remote host actually sent a "host
unreachable" message!

>Bela<
 

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