Re: prefixlen of IPv6 over PPP

[Steven Bellovin <smb%cs.columbia.edu@localhost>]

On Nov 6, 2009, at 12:46 PM, Nagae Hidetake wrote:

> From: "Brian A. Seklecki" <seklecki%noc.cfi.pgh.pa.us@localhost>
> Subject: Re: prefixlen of IPv6 over PPP
> Date: Fri, 06 Nov 2009 11:43:41 -0500
>
> > Very curious.  check some RFCs, or check an XP box.  What is RTADV
> > giving them and what are they accepting?
> >
> > Assigning a /128 to an v6 PPP interface is like assiging a /32 to an
> > IPv4 (/31 is...maybe known to work in some exotic platforms, but..)
>
> In Section 4.1 (Interface Identifier) of RFC 5072 (IP Version 6 over  
> PPP):
>
>  This Configuration Option provides a way to negotiate a unique, 64-
>  bit interface identifier to be used for the address autoconfiguration
>  [3] at the local end of the link (see Section 5).
>
> In Section 5.3 (Creation of Link-Local Addresses) of RFC 4862 (IPv6
> Stateless Address Autoconfiguration):
>
>  If the sum of the link-local prefix length and N is larger than 128,
>  autoconfiguration fails and manual configuration is required.
>
>
> So I think prefixlen should be 64, but I'm not sure...


I wonder if the problem is that it's a ppp interface.  Stateless  
autoconfig is defined for Ethernet-like devices with 6-byte MAC  
addresses that are expanded to 8 bytes per an algorithm.  Maybe the  
NetBSD code doesn't handle the ppp interface type properly with a 64- 
bit prefix.

                --Steve Bellovin, http://www.cs.columbia.edu/~smb