Hello!

On Mon, Feb 03, 2014 at 04:23:00PM +0100, Nicolas Dichtel wrote:

Le 03/02/2014 08:19, Sohny Thomas a écrit :

quoted

quoted

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.

quoted

quoted

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:
<https://bugzilla.kernel.org/show_bug.cgi?id=68511>

Basically, the command in question is this one:

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

which removes the fe80::/64 route.

quoted

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.

quoted

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?

Greetings,

  Hannes