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[v6ops] IPv6 prefix to use to store IPv4 prefixes in an IPv6 IP Address Managment System?

Ray Hunter <v6ops@globis.net> Tue, 17 May 2011 14:09 UTC

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Date: Tue, 17 May 2011 16:09:11 +0200
From: Ray Hunter <v6ops@globis.net>
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To: Mark Smith <ipng@69706e6720323030352d30312d31340a.nosense.org>, "v6ops@ietf.org WG" <v6ops@ietf.org>
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Subject: [v6ops] IPv6 prefix to use to store IPv4 prefixes in an IPv6 IP Address Managment System?
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I recently coded a system where I handled the IPv4 addresses as IPv4 
mapped IPv6 addresses = ::ffff:a.b.c.d addresses in a single table for 
all prefixes for an application. It was convenient in the end, but it 
took quite a lot of code to handle the special human readable forms 
properly.

I can let you have the PERL library if you want.

I would certainly avoid use of deprecated addresses ::0000:a.b.c.d. 
There is some overlap e.g. ::1 & ::0

I also found some problems with libraries handling things like ::ffff:10.0

Another equally valid approach is to use completely separate tables for 
IPv4 and IPv6, depending on your application.

How, for example, in a firewall rules system, would you distinguish a 
match rule for an IPv4 mapped IPv6 address being carried over a native 
IPv6 packet, versus a normal native IPv4 encapsulated packet? You'd 
anyway need to keep track of the encapsulation on the wire.

http://tools.ietf.org/html/draft-itojun-v6ops-v4mapped-harmful-02

Sometimes it's just better to treat IPv4 and IPv6 as completely separate 
address families.

best regards,
RayH

> Subject:
> [v6ops] IPv6 prefix to use to store IPv4 prefixes in an IPv6 IP 
> Address Managment System?
> From:
> Mark Smith <ipng@69706e6720323030352d30312d31340a.nosense.org>
> Date:
> Tue, 17 May 2011 20:44:23 +0930
>
> To:
> v6ops@ietf.org
>
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> 7bit
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> list
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> Message:
> 4
>
>
> Hi,
>
> It recently occurred to me that it could be useful to store IPv4 prefix
> information in an IPv6 IP address management system, so that both IPv4
> and IPv6 prefix information are kept in the same address
> management database.
>
> The only question I have about doing that is what IPv6 prefix to use
> for these IPv4 prefix entries. The deprecated IPv4-Compatible IPv6
> Address format would be convenient for this purpose as all bits
> preceding the IPv4 prefix are zeros, making these entries very easy to
> spot if you happen to be looking at the IPv6 form of them. Would that
> be safe and reasonable to use the ::/96 prefix? Would it be worth me
> writing up an ID proposing the recycing of this form of IPv6 address
> for this purpose?
>
> Thanks,
> Mark.
>
>

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