netdev - Re: [PATCH net-next] ipv6: do not merge differe type and protocol routes

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Date: Fri, 15 Sep 2023 10:23:43 +0800
From: Hangbin Liu <liuhangbin@...il.com>
To: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc: David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Ido Schimmel <idosch@...sch.org>,
	Thomas Haller <thaller@...hat.com>
Subject: Re: [PATCH net-next] ipv6: do not merge differe type and protocol
 routes

On Fri, Sep 01, 2023 at 11:36:51AM +0200, Nicolas Dichtel wrote:
> > I do agree now that protocol is informative (passthrough from the kernel
> > perspective) so not really part of the route. That should be dropped

I'm not sure. Is there any user space route daemon will use this info? e.g. some
BGP route daemon?

> > from the patch leaving just a check on rt_type as to whether the routes
> > are different. From there the append, prepend, replace and change
> > semantics should decide what happens (ie., how the route is inserted).
> Right. What can guide us is the meaning/concept/benefit of having this kind of
> routing table:
> local 2001:db8:103::/64 via 2001:db8:101::10 dev dummy1 metric 1024 pref medium
> 2001:db8:103::/64 via 2001:db8:101::10 dev dummy2 metric 1024 pref medium
> 
> I don't understand how this is used/useful. It's why I ask for the use case/goal
> of this patch.
> How does the user know which route is used?

I'm not sure how user will use it. Maybe just block/forward some traffic to
local first and remove the local route later to unblock them. IPv4 can also
do like this. e.g.

+ ip link add dummy1 up type dummy
+ ip link add dummy2 up type dummy
+ ip addr add 192.168.0.1/24 dev dummy1
+ ip addr add 192.168.0.2/24 dev dummy2
+ ip route add local 192.168.3.0/24 dev dummy1 table 100
+ ip route append unicast 192.168.3.0/24 dev dummy1 table 100
+ ip route append unicast 192.168.3.0/24 dev dummy2 table 100
+ ip route show table 100
local 192.168.3.0/24 dev dummy1 scope host
192.168.3.0/24 dev dummy1 scope link
192.168.3.0/24 dev dummy2 scope link

Thanks
Hangbin