Re: [PATCH] ipv6: default route for link local address is not addedwhile assigning a address

From: Nicolas Dichtel
Date: Mon Feb 03 2014 - 11:26:25 EST

Le 03/02/2014 17:08, Hannes Frederic Sowa a Ãcrit :

On Mon, Feb 03, 2014 at 04:23:00PM +0100, Nicolas Dichtel wrote:
Le 03/02/2014 08:19, Sohny Thomas a Ãcrit :

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.
Sure. It's why I don't like this patch, it fix a user error.

that interface, as a global scoped one is just fine enough) or make flush
remove the link-local address (but this seems a bit too special cased for

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.


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
assumes that the route gets added since the LLA is not removed during the
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@localhost ~]# 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
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.
I don't like this solution, because it's a kernel patch to fix a configuration

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.
This seems right also, but I'm not sure that this will fix Sohny's pb.

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.
Why using this command 'ip -6 route flush proto static' isn't possible?
I think that we know what kind of route is added for these TAHI tests, hence
it's better to remove only routes added manually (or by a routing daemon if
it's the case).
Removing kernel routes may hide bugs: imagine the kernel adds a wrong route,
TAHI will not detect it.

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