PPP IPv6 prefix length and stateless autoconfiguration?
dan.krejsa at windriver.com
Tue Oct 17 17:03:10 UTC 2006
Thanks for your reply! I'm actually working on an OS which uses
a FreeBSD and Kame-derived stack, very similar in its IPv6 code
to the current FreeBSD. The PPP code is of a different derivation,
however. It specifies a 128-bit subnet mask and sets a destination
address for PPP/IPv6 interfaces, and we consequently saw an
issue with IPv6 autoconfiguration. As a workaround, I did exactly
what you suggest, changed the code to configure the interface with a
64-bit prefix without a destination address (actually, the code
tried but failed to set the destination address, but I didn't notice
it at first).
This appears to make the autoconfiguration work fine, and I
encountered no other connectivity issues in brief testing;
but a coworker of mine noticed that ifconfig no longer showed
the destination address, and I investigated and found the
128-bit enforcement in in6_update_ifa(). This makes me somewhat
nervous; but if configuring a PPP/IPv6 interface without an
IPv6 destination address is the intended method of use,
I'd be more comfortable with this. Is that the standard
way of doing things?
From: JINMEI Tatuya / ???? [mailto:jinmei at isl.rdc.toshiba.co.jp]
Sent: Monday, October 16, 2006 7:40 PM
To: Krejsa, Dan
Cc: freebsd-net at freebsd.org
Subject: Re: PPP IPv6 prefix length and stateless autoconfiguration?
>>>>> On Mon, 16 Oct 2006 15:19:55 -0700,
>>>>> "Krejsa, Dan" <dan.krejsa at windriver.com> said:
> Some code in the in6_update_ifa() function in netinet6/in6.c
> enforces that if an IPv6 destination address is specified for
> an interface address, the interface must be point-to-point or
> loopback (fine), and the corresponding prefix length must be
> exactly 128 bits.
> The latter seems (at least naively) to conflict with
> the definition in
> that the interface identifier length for PPP interfaces is 64 bits,
> correspondingly prefixes accepted from a router advertisement
> must also be 64 bits long; see section 5.5.3 in
So shouldn't you simply specify the prefix length of 64 without
specifying the *destination* address of the p2p link?
Communication Platform Lab.
Corporate R&D Center, Toshiba
jinmei at isl.rdc.toshiba.co.jp
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