[afnog] subnet prefix length > 64 breaks IPv6?

sylvain aboka baya abscoco2001 at yahoo.fr
Tue Dec 27 11:30:32 UTC 2011

 Hi, Jordi !

 Please, Receive my Best Wishes about the New Year 2012 !

 FYA, Please Look Below...


Message: 6
Date: Sat, 24 Dec 2011 11:02:35 +0530
From: Glen Kent <glen.kent at gmail.com>
To: nanog at nanog.org
Subject: subnet prefix length > 64 breaks IPv6?
    <CAPLq3UPJqwrqeOJornSAEQjNa=b7BOB6r3XZWugHUGyLAsq9Wg at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1


I am trying to understand why standards say that "using a subnet
prefix length other than a /64 will break many features of IPv6,
including Neighbor Discovery (ND), Secure Neighbor Discovery (SEND)
[RFC3971], .. " [reference RFC 5375]

Or "A number of other features currently in development, or being
proposed, also rely on /64 subnet prefixes."

Is it because the 128 bits are divided into two 64 bit halves, where
the latter identifies an Interface ID which is uniquely derived from
the 48bit MAC address.

I am not sure if this is the reason as this only applies to the link
local IP address. One could still assign a global IPv6 address. So,
why does basic IPv6 (ND process, etc) break if i use a netmask of say

I know that several operators use /120 as a /64 can be quite risky in
terms of ND attacks. So, how does that work? I tried googling but
couldnt find any references that explain how IPv6 breaks with using a
netmask other than 64.



 Best Regards!                                                     
Sylvain Baya
 (+237) 77005341                              

abscoco2001 at yahoo.fr

 De : JORDI PALET MARTINEZ <jordi.palet at consulintel.es>
À : "ipv6cluster at ist-ipv6.org" <ipv6cluster at ist-ipv6.org> 
Envoyé le : Lundi 26 Décembre 2011 8h06
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