ovn: Avoid tunneling for VLAN packets redirected to a gateway chassis

ovn: Avoid tunneling for VLAN packets redirected to a gateway chassis

An OVN deployment can have multiple logical switches each with a
localnet port connected to a distributed logical router in which one
logical switch may provide external connectivity and the rest of
the localnet logical switches use VLAN tagging in the physical
network.

As reported in [1], external traffic from these localnet VLAN tagged
logical switches are tunnelled to the gateway chassis (chassis hosting
a distributed gateway port which applies NAT rules). As part of the
discussion in [1], there are few possible solutions proposed by
Russell [2]. This patch implements the first option in [2].

With this patch, a new option 'reside-on-redirect-chassis' in 'options'
column of Logical_Router_Port table is added. If the value of this
option is set to 'true' and if the logical router also have a
distributed gateway port, then routing for this logical router port
is centralized in the chassis hosting the distributed gateway port.

If a logical switch 'sw0' is connected to a router 'lr0' with the
router port - 'lr0-sw0' with the address - "00:00:00:00:af:12 192.168.1.1"
, and it has a distributed logical port - 'lr0-public', then the
below logical flow is added in the logical switch pipeline
of 'sw0' if the 'reside-on-redirect-chassis' option is set on 'lr-sw0' -

table=16(ls_in_l2_lkup), priority=50,
match=(eth.dst == 00:00:00:00:af:12 && is_chassis_resident("cr-lr0-public")),
action=(outport = "sw0-lr0"; output;)

"cr-lr0-public" is an internal port binding created by ovn-northd of type
'chassisredirect' for lr0-public in SB DB. Please see "man ovn-sb" for more details.

With the above flow, the packet doesn't enter the router pipeline in
the source chassis. Instead the packet is sent out via the localnet
port of 'sw0'. The gateway chassis upon receiving this packet, runs
the logical router pipeline applying NAT rules and sends the traffic
out via the localnet port of the logical switch providing external connectivity.
The gateway chassis will also reply to the ARP requests for the router port IPs.

With this approach, we avoid redirecting the external traffic to the
gateway chassis via the tunnel port. There are a couple of drawbacks
with this approach:

  - East - West routing is no more distributed for the VLAN tagged
    localnet logical switches if 'reside-on-redirect-chassis' option is defined

  - 'dnat_and_snat' NAT rules with 'logical_mac' and 'logical_port'
    columns defined will not work for these logical switches.

This approach is taken for now as it is simple. If there is a requirement
to support distributed routing for these VLAN tenant networks, we
can explore other possible solutions.

[1] -  https://mail.openvswitch.org/pipermail/ovs-discuss/2018-April/046543.html
[2] - https://mail.openvswitch.org/pipermail/ovs-discuss/2018-April/046557.html

Reported-at: https://mail.openvswitch.org/pipermail/ovs-discuss/2018-April/046543.html
Reported-by: venkata anil <vkommadi@redhat.com>
Co-authored-by: venkata anil <vkommadi@redhat.com>
Signed-off-by: Numan Siddique <nusiddiq@redhat.com>
Signed-off-by: venkata anil <vkommadi@redhat.com>
Signed-off-by: Gurucharan Shetty <guru@ovn.org>