If both the router ports point to the same router, then I am not sure
why this would need to be two ports.  Maybe the schema is not sufficient
to report both IPv4 and IPv6 addresses on a single router port; if so,
then I would support enhancing the schema to fix that.

I suspect that for connecting to two different routers, it is possible
to instead connect one router and then connect that router to others in
a way that accomplishes an equivalent goal.  I haven't thought it
through though.

On Thu, Jul 30, 2015 at 09:12:14PM +0300, Gal Sagie wrote:
> Yes, i checked this on my setup.
> For example, you can have both IPv6 and IPv4 subnets per the same network
> (which maps to a logical switch)
> and connect both as two different router ports (to the same router)
> 
> You can also connect the same network to two different routers, i am not
> sure if you need the extra route extension for that or not, i think you
> could
> configure it as default gateway with out this extension, but with the
> extension you
> can define routing between the two routers.
> 
> 
> 
> 
> 
> On Thu, Jul 30, 2015 at 9:03 PM, Ben Pfaff <b...@nicira.com> wrote:
> 
> > [adding Aaron Rosen]
> >
> > On Wed, Jul 29, 2015 at 12:20:30PM +0300, Gal Sagie wrote:
> > > Currently Neutron support defining few subnets (IP cidrs) on a network
> > > (logical switch)
> > > and connecting them to the same router (or different routers).
> > > Currently in the NB schema, the logical switch can be connected only to
> > one
> > > logical
> > > router port.
> > >
> > > This needs to be extended so a logical switch can have more then one
> > > logical router
> > > port reference to support the above use case.
> >
> > Limiting a logical switch to a single router port is an intentional
> > design decision.  It means that a packet traverses at most two logical
> > switches (one at ingress, one at egress), which simplifies some of the
> > logical switch design, and it prevents loops.
> >
> > VMware's NVP controller uses the same design, for those reasons and
> > others.  The NVP paper from NSDI 2014 (see
> > http://benpfaff.org/papers/net-virt.pdf) puts it this way:
> >
> >     As an optimization, we constrain the logical topology such that
> >     logical L2 destinations can only be present at its edge[6].  This
> >     restriction means that the OVS flow table of a sending hypervisor
> >     needs only to have flows for logical datapaths to which its local
> >     VMs are attached as well as those of the L3 routers of the logical
> >     topology; the receiving hypervisor is determined by the logical IP
> >     destination address, leaving the last logical L2 hop to be executed
> >     at the receiving hypervisor.
> >
> >     [6] We have found little value in supporting logical routers
> >         interconnected through logical switches without tenant VMs.
> >
> > Are you sure that Neutron supports multiple router ports per switch?
> > Russell Bryant (in IRC) and Aaron Rosen (in a quick in-person chat)
> > seemed doubtful.
> >
> 
> 
> 
> -- 
> Best Regards ,
> 
> The G.
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