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
[off-list ref] wrote:

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Hello,

On 12.09.2016 16:27, Andreas Hübner wrote:

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I have the following setup:
  - 2 directly connected hosts (A+B), both have only link local addresses
    configured (interface on both hosts is eth0)

           :

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      fe80::/64 dev eth1  proto kernel  metric 256
      fe80::/64 dev eth0  proto kernel  metric 256

           :

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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)

   :

quoted

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 [off-list ref]
Technical Division, MIRACLE LINUX CORPORATION