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Date:      Thu, 22 Apr 1999 23:45:06 -0400
From:      Chris Johnson <cjohnson@palomine.net>
To:        "Bruce A. Mah" <bmah@CA.Sandia.GOV>
Cc:        stable@FreeBSD.ORG
Subject:   Re: netstat -r (fwd)
Message-ID:  <19990422234506.A14538@palomine.net>
In-Reply-To: <199904230125.SAA28802@stennis.ca.sandia.gov>; from Bruce A. Mah on Thu, Apr 22, 1999 at 06:25:25PM -0700
References:  <199904230059.TAA08580@alecto.physics.uiuc.edu> <199904230125.SAA28802@stennis.ca.sandia.gov>

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On Thu, Apr 22, 1999 at 06:25:25PM -0700, Bruce A. Mah wrote:
> If memory serves me right, Igor Roshchin wrote:
> 
> > Check the traceroute I pasted below - that router 10.0.232.27
> > is not on my internal network. (I have NO private IP addresses).
> > So, are you saying I need to have all 2^512  (18609625)  in my
> > /etc/hosts file ????
> 
> No...it's just that you shouldn't ask Internet nameservers to resolve 
> address-to-name lookups for private networks.  HOWEVER, that said...
> 
> > traceroute to www.home.net (24.0.30.175), 30 hops max, 40 byte packets
> 
> ...you're seeing a rather unfortunate, pathological case.  The 10/net 
> addresses in this case are a part of @Home which, for some reason that 
> completely eludes me, uses private addresses inside its backbone network.  
> Although you can't route to intermediate hosts, you can route to endsystems 
> inside the @Home network.  I imagine there's a reason for this, but it 
> violates the various RFCs that have already been cited.

This is from http://www.worldgate.com/~marcs/mtu (an article on Path MTU
Discovery and Filtering ICMP). I believe it answers the question of why you'd
see RFC 1918 addresses when you do a traceroute:

"On many routers, a separate IP address in the same subnet is required for each
end of a point to point link. This can use address space if there are a large
number of such links. Since the actual address of the links doesn't appear to
impact much, many people use RFC 1918 private address space for such links."

Chris


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