Re: [v6ops] draft-moreiras-v6ops-rfc3849bis-00

Owen DeLong <> Mon, 12 August 2013 17:11 UTC

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From: Owen DeLong <>
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Date: Mon, 12 Aug 2013 09:54:37 -0700
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To: Mark Andrews <>
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Cc: Alejandro Acosta <>,
Subject: Re: [v6ops] draft-moreiras-v6ops-rfc3849bis-00
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On Aug 11, 2013, at 16:38 , Mark Andrews <> wrote:

> In message <>om>, Owen DeLong write
> s:
>> I support the idea. It might be worth also asking for a ULA Doc slice at the 
>> same time.  I think a /48 is probably sufficient for most ULA examples.
>> But I think it would be good to be able to write up ULA examples and training
>> that use actual ULA prefixes intended for documentation.
> Why?
> The purpose of reserving a prefix for documentation is to ensure
> that documentation prefixes doesn't clash with ones assigned by a
> registries.  For locally assigned ULA don't need a reserved prefix
> because there is no registry assignments to clash with.  For centrally
> assigned ULA there is no registry yet so no practical examples can
> exist.  When such a registry is assigned we can document a prefix in the
> meantime just generate a new prefix when you write your documentation.
> 	dd if=/dev/random bs=5 count=1 | od -tx1 |
> 	awk '/000000/ { print "fd" $2 ":" $3 $4 ":" $5 $6 ; exit}

Because, as history has shown, if there isn't a prefix documented as "you
should use this for documentation and training only", people tend to copy
examples verbatim instead.

Admittedly, I still run into the occasional internal network numbered out
of doc-prefix space in IPv4 because they copied the examples, but I run
into a lot more cases where they improperly copied examples that used
other prefixes than the documentation prefix.

The point of a documentation prefix is not only to avoid clashing with
registry space. It is also so that if you blindly copy examples, this fact
is instantly obvious to any network engineer who knows what they are
doing and can be more easily identified and corrected (hopefully before
it becomes entrenched beyond repair).