[RFE][L3][OVS] use controller (ovs-agent) send (packet-out) RA to (VMs) ports

[LIU Yulong]

Currently neutron l3 router will run radvd to send out RA packets about the ManagedFlag, LinkMTU and prefix of IPv6 subnet. But rememeber we have a distributed SDN controller, aka ovs-agent, which can do this work more naturally and gracefully.

Current radvd config looks like this:

interface qr-8fd65326-c4
{
   AdvSendAdvert on;
   MinRtrAdvInterval 30;
   MaxRtrAdvInterval 100;
   AdvLinkMTU 1500;
   AdvManagedFlag on;
   prefix fda7:a5cc:3460:3::/64
   {
        AdvOnLink on;
        AdvAutonomous off;
   };
};

While RYU supports Router Advertisement:
https://ryu.readthedocs.io/en/latest/library_packet_ref/packet_icmpv6.html#ryu.lib.packet.icmpv6.nd_router_advert

This can narrow down the burden of L3-agent management and run less process for a router.

[Oleg Bondarev (obondarev)]

So this will have full feature parity with current solution for RA, right?

[LIU Yulong (dragon889)]

Yes, it will be. The most important part of radvd is to send RA packet periodically, and as we know ovs-agent has every information of a port, so this work should be easily and simply.

[Slawek Kaplonski (slaweq)]

IIUC with such change, we will have IPv6 DHCP with SLAAC even in networks not connected to any router, right?

[Brian Haley (brian-haley)]

And I guess this would also support responding to solicitations based on the class below the one you linked, nd_router_solicit ? I believe radvd will respond to RS messages which are sometimes sent on link-up.

[LIU Yulong (dragon889)]

@Slawek, yes, that's right, gateway port is not needed anymore. For (VM) port, it has IPv6 addresses from subnets, the controller will send each subnet's infos to it. Then the rest work will be the configuration of the OS (Linux/windows) or users' choices.

@Brian, I never try such configurations for interacting the neutron router and physical router. But I can image an solution is that RS maybe can be implemented as a RS_Responder on network nodes, something like ARP responder, when the router setup external gateway and internal interface, add related RS_Responder flows to the ovs-bridge. If the native ovs-flows can not do that work, send the RS to ovs-agent, let the controller response that.

[Lajos Katona (lajos-katona)]

During last drivers meeting we approved this RFE (see [0]) with the condition that it will an agent extension.

[0]: https://meetings.opendev.org/meetings/neutron_drivers/2022/neutron_drivers.2022-02-25-14.00.log.html#l-14

[LIU Yulong (dragon889)]

Yes, this will be a new agent extension as well, similar to distributed DHCP for ovs agent [1]. Make new feature configurable, that's my precept.

[1] https://review.opendev.org/c/openstack/neutron/+/776567

[OpenStack Infra (hudson-openstack)]

Related fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/neutron-specs/+/832660

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Slawek Kaplonski <email address hidden>" on branch: master
Review: https://review.opendev.org/c/openstack/neutron-specs/+/832660
Reason: This review is > 4 weeks without comment, and failed Zuul jobs the last time it was checked. We are abandoning this for now. Feel free to reactivate the review by pressing the restore button and leaving a 'recheck' comment to get fresh test results.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/neutron-specs/+/832660
Committed: https://opendev.org/openstack/neutron-specs/commit/49b415960c291f3f0a1aa967a1714b7e8ca31aef
Submitter: "Zuul (22348)"
Branch: master

commit 49b415960c291f3f0a1aa967a1714b7e8ca31aef
Author: LIU Yulong <email address hidden>
Date: Tue Mar 8 23:12:51 2022 +0800

    Spec for Router Advertisement on Openvswitch Agent

    Related-Bug: #1961011
    Change-Id: I9255ed2df6003768878d275c706330be916f7bd9