[ovs-dev] OpenStack Proposal: Integration with OVN L3 Gateway

[Kyle Mestery]

On Tue, Jun 7, 2016 at 3:50 PM, Amitabha Biswas <azbiswas at gmail.com> wrote:
> This proposal outlines the modifications needed in networking-ovn (addresses https://bugs.launchpad.net/networking-ovn/+bug/1551717 <https://bugs.launchpad.net/networking-ovn/+bug/1551717>) to provide Floating IP (FIP) and SNAT using the L3 gateway router patches listed below:
>
> http://patchwork.ozlabs.org/patch/624312/ <http://patchwork.ozlabs.org/patch/624312/>
> http://patchwork.ozlabs.org/patch/624313/ <http://patchwork.ozlabs.org/patch/624312/>
> http://patchwork.ozlabs.org/patch/624314/ <http://patchwork.ozlabs.org/patch/624312/>
> http://patchwork.ozlabs.org/patch/624315/ <http://patchwork.ozlabs.org/patch/624312/>
> http://patchwork.ozlabs.org/patch/629607/ <http://patchwork.ozlabs.org/patch/629607/>
>
> Diagram:
>
> +-------+                       +-------+
> | NET 1 |                       | NET 2 |
> +-------+                       +-------+
>    |                               |
>    |           *********           |
>    |         **         **         |
>    |       **    *  *     **       |
>    +---RP1 *      DR       * RP2 --+
>            **    *  *     **
>              **         **
>                *********
>                   DTRP (168.254.128.2)
>                    |
>                    |
>                    |
>            +------------------+
>            | Transit Network  |
>            | 169.254.128.0/30 |
>            +------------------+
>                    |
>                    |
>                    |
>                    |
>                   GTRP (169.254.128.1)
>                 *******
>               **       **
>             **   *   *   **                 +------------------+
>             *     GW      *-----------------| Provider Network |
>             **   *   *   **                 +------------------+
>               **       **
>                 *******
>
> New Entities:
>
> OVN Join/Transit Networks
> One per Neutron Router - /30 address space with only 2 ports for e.g. 169.254.128.0/30
> Created when an external gateway is added to a router.
> One extra datapath per router with an External Gateway.
> (Alternate option - One Transit Network in a deployment, IPAM becomes a headache - Not discussed here).
> Prevent Neutron from using that /30 address space. Specify in networking-ovn con file.
> Create 1 new “Join” neutron network (to represent all Join OVN Networks) in the networking-ovn.
> Note that it may be possible to replace the Join/Transit network using Router Peering in later versions  (not discussed here).
> Allocate 2 ports in the Join network in the networking-ovn plugin.
> Logical Gateway Transit Router Port (gtrp), 169.254.128.1
> Logical Distributed Transit Router Port (dtrp), 169.254.128.2
> Note that Neutron only sees 1 Join network with 2 ports; OVN sees a replica of this Join network as a new Logical Switch for each Gateway Router. The mapping of OVN Logical Switch(es) Join(s) to Gateway Router is discussed in OVN (Default) Gateway Routers below.
> Note that the MAC addresses of lgrp and lip will be the same on each OVN Join Network, but because they are in different branches of the network topology it doesn’t matter.
> OVN (Default) Gateway Routers:
> One per Neutron Router.
> 2 ports
> Logical Gateway Transit Router Port (gtrp), 169.254.128.1 (same for each OVN Join network).
> External/Provider Router Port (legwrp), this is allocated by neutron.
> Scheduling - The current OVN gateway proposal relies on the CMS/nbctl to decide on which hypervisor (HV) to schedule a particular gateway router.
> A setting on the chassis (new external_id key or a new column) that allows the hypervisor admin to specify that a chassis can or cannot be used to host a gateway router (similar to a network node in OpenStack). Default - Allow (for compatibility purposes).
> The networking-ovn plugin picks up the list of “candidate” chassis from the Southbound DB and uses an existing scheduling algorithm
> Use a simple random.choice i.e. ChanceScheduler (Version 1)
> Tap into the neutron’s LeastRouterScheduler - but that requires the networking-ovn (or some a hacked up version of the L3 agent) to imitate the L3 agent running on various network nodes.
> Populate the SNAT and DNAT columns in the logical router table. This is under review in OVS - http://openvswitch.org/pipermail/dev/2016-June/072169.html <http://openvswitch.org/pipermail/dev/2016-June/072169.html>
> Create static routing entry in the gateway router to route tenant bound traffic to the distributed logical router.ar gate
>
> Existing Entities:
>
> Distributed Logical Routers:
> Set the default gateway of the distributed logical router to the IP Address of the corresponding Logical Gateway Transit Router Port (169.254.128.1).
>
> It would be good to get some feedback on this strategy. Guru mentioned that he saw a need for ARP response across multiple gateway routers, we don’t see that requirement in this design/use-case.
>

Amitabha, thanks for writing this up and sending it out! However, the
formating is really bad (I blame Notes). It's also bad in the archives
of the openstack-dev ML [1]. It may make sense to put this on an
etherpad or something so it's easier to digest.

Overall, the proposal does make sense and I'm excited to hear feedback
from others.

Thanks!
Kyle

[1] http://lists.openstack.org/pipermail/openstack-dev/2016-June/096806.html

> Thanks
> Amitabha (azbiswas) and Chandra (chandrav)
>
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