[PATCH net-next] ipv6: do not set "u" bit for temporary addresses

[PATCH net-next] ipv6: do not set "u" bit for temporary addresses

[Florent Fourcot]

The bit 6 of interface identifier was before the "universal/local bit",
indicating local significance only. This rule is now obsoleted by the
RFC 7136, removing all significance of bits in interface identifier.

The new rule is "In all cases, the bits in an IID have no generic
semantics; in other words, they have opaque values.", so we can remove
the setting of bit 6, it will improve the entropy of random addresses.

Signed-off-by: Florent Fourcot <florent.fourcot@enst-bretagne.fr>
---
 net/ipv6/addrconf.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index ad23569..0b2a18e 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -1878,7 +1878,6 @@ static void __ipv6_regen_rndid(struct inet6_dev *idev)
 {
 regen:
 	get_random_bytes(idev->rndid, sizeof(idev->rndid));
-	idev->rndid[0] &= ~0x02;
 
 	/*
 	 * <draft-ietf-ipngwg-temp-addresses-v2-00.txt>:
-- 
1.8.5.3

Re: [PATCH net-next] ipv6: do not set "u" bit for temporary addresses

[Hannes Frederic Sowa]

On Wed, Feb 12, 2014 at 12:08:06PM +0100, Florent Fourcot wrote:
> The bit 6 of interface identifier was before the "universal/local bit",
> indicating local significance only. This rule is now obsoleted by the
> RFC 7136, removing all significance of bits in interface identifier.
> 
> The new rule is "In all cases, the bits in an IID have no generic
> semantics; in other words, they have opaque values.", so we can remove
> the setting of bit 6, it will improve the entropy of random addresses.
> 
> Signed-off-by: Florent Fourcot <florent.fourcot@enst-bretagne.fr>

Hmm, the RFC only talks about new methods of IID generation. Not sure
if old software depends on that. I actually know about one commercial
available ip management system which does make use of those bits to
classify ipv6 addresses for displaying purposes (that's how I actually
learned about those bits ;) ).

Greetings,

  Hannes

Re: [PATCH net-next] ipv6: do not set "u" bit for temporary addresses

[David Miller]

From: Florent Fourcot <florent.fourcot@enst-bretagne.fr>
Date: Wed, 12 Feb 2014 12:08:06 +0100

> The bit 6 of interface identifier was before the "universal/local bit",
> indicating local significance only. This rule is now obsoleted by the
> RFC 7136, removing all significance of bits in interface identifier.
> 
> The new rule is "In all cases, the bits in an IID have no generic
> semantics; in other words, they have opaque values.", so we can remove
> the setting of bit 6, it will improve the entropy of random addresses.
> 
> Signed-off-by: Florent Fourcot <florent.fourcot@enst-bretagne.fr>

I'm hesistent to apply this given the feedback you've been given.

Re: [PATCH net-next] ipv6: do not set "u" bit for temporary addresses

[Florent Fourcot]

> 
> I'm hesistent to apply this given the feedback you've been given.


I understand. I will try to found more convincing references, and
re-send the patch.

Regards,

-- 
Florent.