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Date:	Mon, 3 Feb 2014 17:08:38 +0100
From:	Hannes Frederic Sowa <>
To:	Nicolas Dichtel <>
Cc:	Sohny Thomas <>,
	netdev <>,,,,
	kumuda <>
Subject: Re: [PATCH] ipv6: default route for link local address is not added while assigning a address


On Mon, Feb 03, 2014 at 04:23:00PM +0100, Nicolas Dichtel wrote:
> Le 03/02/2014 08:19, Sohny Thomas a écrit :
> >
> >>Actually I am not so sure, there is no defined semantic of flush. I would
> >>be ok with all three solutions: leave it as is, always add link-local
> >>address (it does not matter if we don't have a link-local address on
> It matters. This address is required.
> RFC 4291
> Section 2.1:
>    All interfaces are required to have at least one Link-Local unicast
>    address (see Section 2.8 for additional required addresses).
> Section 2.8:
>       o Its required Link-Local address for each interface.

Yes, sure, it is required. But you also can manually delete the LL address and
we don't guard against that.

> >>that interface, as a global scoped one is just fine enough) or make flush 
> >>not
> >>remove the link-local address (but this seems a bit too special cased for 
> >>me).
> >
> >1) In case if we leave it as it is, there is rfc 6724 rule 2 to be 
> >considered (
> >previously rfc 3484)
> >
> >Rule 2: Prefer appropriate scope.
> >    If Scope(SA) < Scope(SB): If Scope(SA) < Scope(D), then prefer SB and
> >    otherwise prefer SA.  Similarly, if Scope(SB) < Scope(SA): If
> >    Scope(SB) < Scope(D), then prefer SA and otherwise prefer SB.
> >
> >Test:
> >
> >    Destination: fe80::2(LS)
> >     Candidate Source Addresses: 3ffe::1(GS) or fec0::1(SS) or LLA(LS)
> >     Result: LLA(LS)
> >     Scope(LLA) < Scope(fec0::1): If Scope(LLA) < Scope(fe80::2),  no, 
> >     prefer LLA
> >     Scope(LLA) < Scope(3ffe::1): If Scope(LLA) < Scope(fe80::2),  no, 
> >     prefer LLA
> >
> >
> >Now the above test fails since the route itself is not present, and the 
> >test
> >assumes that the route gets added since the LLA is not removed during the 
> >test
> In your scenario, the link local route has been removed manually, not by the
> kernel. What is your network manager?

The test scenario is outlined here:

Basically, the command in question is this one:

	[root@...alhost ~]# ip -6 -statistics -statistics route flush dev eth0

which removes the fe80::/64 route.

> >2) having a LLA always helps in NDP i think
> A link-local Address yes, it's a MUST. But having only the link local route 
> will
> not help.

Agreed, the LL address should be available, too. I currently don't know
what will break if LL address is not available. I guess MLD won't work
properly and thus even basic connectivity won't work with some switches.

> >3) making flush not remove link-local address will be chnaging 
> >functionality of
> >ip flush command
> You can flush by specifying the prototype:
> ip -6 route flush proto static

So we have four possiblities now:

1) leave it as is

	seems still acceptable to me

2) add fe80::/64 route unconditionally if any address gets added

	Sohny's patch already looks good in doing so at first look.

3) add fe80::/64 route in case LL address gets added via inet6_rtm_newaddr

	would be ok, too. I tend towards this solution somehow by now.

4) make flush not remove the fe80::/64 address

	Least favourable to me. I guess this also woud need iproute change
	and seems most difficult to do.

Any opionions?



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