netdev - Re: [PATCH net-next v2 6/6] vxlan: allow multiple VXLANs with same VNI for IPv6 link-local addresses

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Date:   Sun, 16 Apr 2017 17:15:42 +0200
From:   Matthias Schiffer <mschiffer@...verse-factory.net>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     davem@...emloft.net, jbenc@...hat.com, hannes@...essinduktion.org,
        pshelar@....org, aduyck@...antis.com, roopa@...ulusnetworks.com,
        netdev@...r.kernel.org, dev@...nvswitch.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2 6/6] vxlan: allow multiple VXLANs with same
 VNI for IPv6 link-local addresses

On 04/14/2017 07:38 PM, Stephen Hemminger wrote:
> On Fri, 14 Apr 2017 18:44:46 +0200
> Matthias Schiffer <mschiffer@...verse-factory.net> wrote:
> 
>> As link-local addresses are only valid for a single interface, we can allow
>> to use the same VNI for multiple independent VXLANs, as long as the used
>> interfaces are distinct. This way, VXLANs can always be used as a drop-in
>> replacement for VLANs with greater ID space.
>>
>> This also extends VNI lookup to respect the ifindex when link-local IPv6
>> addresses are used, so using the same VNI on multiple interfaces can
>> actually work.
>>
>> Signed-off-by: Matthias Schiffer <mschiffer@...verse-factory.net>
> 
> Why does this have to be IPv6 specific?

I'm not familar with IPv4 link-local addresses and how route lookup works
for them. vxlan_get_route() sets flowi4_oif to the outgoing interface; does
__ip_route_output_key_hash() do the right thing for link-local addresses
when such addresses are used on multiple interfaces? I see some special
casing for multicast destinations, but none for link-local ones.

> 
> What about the case where VXLAN is not bound to an interface?
> If that is used then that could be a problem.
> 

With patch 4/6, link-local IPv6 addresses can't be configured without an
interface anymore.

Matthias



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