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

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Message-ID: <ZQPUMchAuQma7Xrh@Laptop-X1>
Date: Fri, 15 Sep 2023 11:49:05 +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 11:50:12AM +0200, Nicolas Dichtel wrote:
> > + ip -6 route flush table 300
> > + ip link add dummy1 up type dummy
> > + ip link add dummy2 up type dummy
> > + ip addr add 2001:db8:101::1/64 dev dummy1
> > + ip addr add 2001:db8:101::2/64 dev dummy2
> > + ip route add local 2001:db8:103::/64 via 2001:db8:101::10 dev dummy1 table 100
> > + ip route append unicast 2001:db8:103::/64 via 2001:db8:101::10 dev dummy1 table 100
> > RTNETLINK answers: File exists
> > 
> >      ^^ here the append still failed
> And if I play a little bit of the devil's advocate: why is it rejected? It's not
> the same route, the types differ :)

This is actually for compatibility...
> 
> > 
> > + ip route append unicast 2001:db8:103::/64 via 2001:db8:101::10 dev dummy2 table 100
> > + ip -6 route show table 100
> > 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
> 
> What is the purpose of such a routing table?

As I replied in last mail. I don't have a clear purpose. A user may use
the local route to block traffic temporary.

> How is the gateway of a local route used by the kernel?

I don't know. IPv6 support this since beginning...

> Which route will be used when a packet enters the stack?

The first one it find?

Thanks
Hangbin