netdev - Re: icmpv6: issue with routing table entries from link local addresses

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Date:   Tue, 13 Sep 2016 12:01:18 +0900
From:   YOSHIFUJI Hideaki <hideaki.yoshifuji@...aclelinux.com>
To:     Sowmini Varadhan <sowmini05@...il.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:     hideaki.yoshifuji@...aclelinux.com,
        Andreas Hübner <andreas@....de>,
        netdev <netdev@...r.kernel.org>,
        "d. caratti" <davide.caratti@...il.com>,
        Sowmini Varadhan <sowmini.varadhan@...cle.com>
Subject: Re: icmpv6: issue with routing table entries from link local
 addresses

Sowmini Varadhan wrote:
> On Mon, Sep 12, 2016 at 1:26 PM, Hannes Frederic Sowa
> <hannes@...essinduktion.org> wrote:
>> Hello,
>>
>> On 12.09.2016 16:27, Andreas Hübner wrote:
> 
>>>
>>> I have the following setup:
>>>   - 2 directly connected hosts (A+B), both have only link local addresses
>>>     configured (interface on both hosts is eth0)
>            :
>>>       fe80::/64 dev eth1  proto kernel  metric 256
>>>       fe80::/64 dev eth0  proto kernel  metric 256
>            :
>>> The issue I currently have is, that the echo reply that host B should
>>> generate is never sent back to host A. If I change the order of the
>>> routing table entries on host B, everything works fine.
>>> (host A is connected on eth0)
>    :
>> This shouldn't be the case. We certainly carry over the ifindex of the
>> received packet into the routing lookup of the outgoing packet, thus the
>> appropriate rule, with outgoing ifindex should be selected.
> 
> Like Hannes,  I too would first check "is B sending out the echo-resp? on
> which interface?".
> 
> But a couple of unexpected things I noticed in linux: the link-local
> prefix should have a prefixlen of /10 according to
> http://www.iana.org/assignments/ipv6-address-space/ipv6-address-space.xhtml
> but "ip -6 route show"  lists this as a /64..

Do not be confused; link-local address for ethernet is described by
IPv6 over FOO document (e.g., RFC2464 for Ethernet).  The address
(fe80::/64 for Ethernet, for example) is defined inside the link-local
scope unicast address space (/10).

-- 
Hideaki Yoshifuji <hideaki.yoshifuji@...aclelinux.com>
Technical Division, MIRACLE LINUX CORPORATION