IPv6 Netowrk Device Numbering BP

Thu Nov 1 19:58:47 UTC 2012

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On 11/1/2012 1:59 PM, Valdis.Kletnieks at vt.edu wrote:
> On Thu, 01 Nov 2012 14:28:48 +0100, "Miquel van Smoorenburg" said:
> 
>> We use a /120 subnet for servers to prevent the NDP cache
>> exhaustion attack. We do maintain a mapping between IPv4 and IPv6
>> addresses; it's simply 2001:db8:vv:ww::xx, where xx is the hex
>> value of the last octet of the IPv4 address.
> 
> ooh.. that's a clever approach I hadn't seen before.  Who should we
> credit for this one?
> 

/120 works well until you get > 99 (if you want the decimal
representations of addresses to look the same)... or if your techs
understand hex.

10.0.0.123 <-> 2001:db8:vv:ww::7b

I have used /116 in the past.  This gives you 1-fff at the end.

10.0.0.123 <-> 2001:db8:vv:ww::123

Hopefully, this is future proof(ish) in that IPv6 only hosts (...when
that happens...) on the same subnet can use
2001:db8:vv:ww::[a-f][0-f][0-f] without danger of collisions with
IPv4/IPv6 hosts.

- -DMM
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