From owner-freebsd-isp  Wed Sep 20 11:49:29 2000
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To: adrianbsd@globalpc.net
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Subject: Re: Using 'private net' IPs for WAN Addresses
From: sthaug@nethelp.no
In-Reply-To: Your message of "Wed, 20 Sep 2000 13:37:04 -0500"
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Date: Wed, 20 Sep 2000 20:49:23 +0200
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> Over the years I've seen several ISPs use 192.168.x.x or other of the IP
> ranges reserved for private networks as WAN adressess for point-to-point
> links on the Internet.
> 
> Personally, I've always felt this to be a bad idea, but I can't come up
> with a compelling reason to convince people not to do it.  Is there a
> reason not to?  or is it just a matter of keeping apples and oranges in
> their respective baskets?

A lot of ISPs today drop packets with RFC 1918 source addresses at the
boundary routers. This means that using 192.168.x.x (or other RFC 1918
addresses) can break PMTU discovery, traceroute etc. that depend on
ICMPs being returned.

Steinar Haug, Nethelp consulting, sthaug@nethelp.no


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