Maybe I'm misreading this but...

I Am Not An Isp patrick at ianai.net
Sat Oct 17 20:25:16 UTC 1998


At 08:07 PM 10/17/98 +0000, Michael Shields wrote:
>In article <4.0.1.19981016224901.00de6240 at pariah.cncx.com>,
>I Am Not An Isp <patrick at ianai.net> wrote:
>> FACT: RFC1918 space does not break PMTU discovery.  Deal with it.
>
>If you use RFC 1918 space on the Internet, PMTU very well may not work
>for you.  You can place fault on whatever standard you like but that
>doesn't change the *operational* issue.

Mark and I have discussed this in private.  I believe this has devolved
into an argument over semantics.

Assume you use RFC1918 addressing in a private enterprise.  PMTU-D will
work without a problem within that enterprise (unless you filter your own
routers).  QED: RFC1918 does not break PMTU-D.  However, if packets from
RFC1918 ports leave the enterprise, then there is a very real possibility
those packets will be filtered on other networks.  These filters are in no
way wrong, bad or otherwise a problem.  It's just something you have to
deal with "operationally".

So, using RFC1918 addresses on router ports which have any possibility of
send packets (even ICMP one-way communication) to other networks may find
their packets filtered.  This means that things like PMTU-D will break.
Not using RFC1918 addressing reduces this possibility because (as Mark
pointed out) these filters are recommended by the RFC.

Does that make everyone happy?  Can we get back to our regularly scheduled
furniture, carpet and spam discussions? :)

>Shields, CrossLink.

TTFN,
patrick

I Am Not An Isp
www.ianai.net
"Think of it as evolution in action." - Niven & Pournelle



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