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It should be noted that "send_arp_for_ha" is a configuration option
that preceded the more recent in-progress work to add VRRP controlled
HA to Neutron's router.  The option was added, I believe, to cause the
router to send (default) 3 GARPs to the external gateway if the router
was removed from one network node and added to another by some
external script or manual intervention.  It did not send anything on
the internal network ports.

VRRP is a different story and the code in review [1] sends GARPs on
internal and external ports.

Hope this helps avoid confusion in this discussion.

Carl

[1] https://review.openstack.org/#/c/70700/37/neutron/agent/l3_ha_agent.py

On Mon, Sep 1, 2014 at 8:52 PM, Xu Han Peng <pengxuhan at gmail.com> wrote:
> Anthony,
>
> Thanks for your reply.
>
> If HA method like VRRP are used for IPv6 router, according to the VRRP RFC
> with IPv6 included, the servers should be auto-configured with the active
> router's LLA as the default route before the failover happens and still
> remain that route after the failover. In other word, there should be no need
> to use two LLAs for default route of a subnet unless load balance is
> required.
>
> When the backup router become the master router, the backup router should be
> responsible for sending out an unsolicited ND neighbor advertisement with
> the associated LLA (the previous master's LLA) immediately to update the
> bridge learning state and sending out router advertisement with the same
> options with the previous master to maintain the route and bridge learning.
>
> This is shown in http://tools.ietf.org/html/rfc5798#section-4.1 and the
> actions backup router should take after failover is documented here:
> http://tools.ietf.org/html/rfc5798#section-6.4.2. The need for immediate
> messaging sending and periodic message sending is documented here:
> http://tools.ietf.org/html/rfc5798#section-2.4
>
> Since the keepalived manager support for L3 HA is merged:
> https://review.openstack.org/#/c/68142/43. And keepalived release 1.2.0
> supports VRRP IPv6 features ( http://www.keepalived.org/changelog.html, see
> Release 1.2.0 | VRRP IPv6 Release). I think we can check if keepalived can
> satisfy our requirement here and if that will cause any conflicts with
> RADVD.
>
> Thoughts?
>
> Xu Han
>
>
> On 08/28/2014 10:11 PM, Veiga, Anthony wrote:
>
>
>
> Anthony and Robert,
>
> Thanks for your reply. I don't know if the arping is there for NAT, but I am
> pretty sure it's for HA setup to broadcast the router's own change since the
> arping is controlled by "send_arp_for_ha" config. By checking the man page
> of arping, you can find the "arping -A" we use in code is sending out ARP
> REPLY instead of ARP REQUEST. This is like saying "I am here" instead of
> "where are you". I didn't realized this either until Brain pointed this out
> at my code review below.
>
>
> That’s what I was trying to say earlier.  Sending out the RA is the same
> effect.  RA says “I’m here, oh and I’m also a router” and should supersede
> the need for an unsolicited NA.  The only thing to consider here is that RAs
> are from LLAs.  If you’re doing IPv6 HA, you’ll need to have two gateway IPs
> for the RA of the standby to work.  So far as I know, I think there’s still
> a bug out on this since you can only have one gateway per subnet.
>
>
>
> http://linux.die.net/man/8/arping
>
> https://review.openstack.org/#/c/114437/2/neutron/agent/l3_agent.py
>
> Thoughts?
>
> Xu Han
>
>
> On 08/27/2014 10:01 PM, Veiga, Anthony wrote:
>
>
> Hi Xuhan,
>
> What I saw is that GARP is sent to the gateway port and also to the router
> ports, from a neutron router. I’m not sure why it’s sent to the router ports
> (internal network). My understanding for arping to the gateway port is that
> it is needed for proper NAT operation. Since we are not planning to support
> ipv6 NAT, so this is not required/needed for ipv6 any more?
>
>
> I agree that this is no longer necessary.
>
>
> There is an abandoned patch that disabled the arping for ipv6 gateway port:
> https://review.openstack.org/#/c/77471/3/neutron/agent/l3_agent.py
>
> thanks,
> Robert
>
> On 8/27/14, 1:03 AM, "Xuhan Peng" <pengxuhan at gmail.com> wrote:
>
> As a follow-up action of yesterday's IPv6 sub-team meeting, I would like to
> start a discussion about how to support l3 agent HA when IP version is IPv6.
>
> This problem is triggered by bug [1] where sending gratuitous arp packet for
> HA doesn't work for IPv6 subnet gateways. This is because neighbor discovery
> instead of ARP should be used for IPv6.
>
> My thought to solve this problem turns into how to send out neighbor
> advertisement for IPv6 routers just like sending ARP reply for IPv4 routers
> after reading the comments on code review [2].
>
> I searched for utilities which can do this and only find a utility called
> ndsend [3] as part of vzctl on ubuntu. I could not find similar tools on
> other linux distributions.
>
> There are comments in yesterday's meeting that it's the new router's job to
> send out RA and there is no need for neighbor discovery. But we didn't get
> enough time to finish the discussion.
>
>
> Because OpenStack runs the l3 agent, it is the router.  Instead of needing
> to do gratuitous ARP to alert all clients of the new MAC, a simple RA from
> the new router for the same prefix would accomplish the same, without having
> to resort to a special package to generate unsolicited NA packets.  RAs must
> be generated from the l3 agent anyway if it’s the gateway, and we’re doing
> that via radvd now.  The HA failover simply needs to start the proper radvd
> process on the secondary gateway and resume normal operation.
>
>
> Can you comment your thoughts about how to solve this problem in this
> thread, please?
>
> [1] https://bugs.launchpad.net/neutron/+bug/1357068
>
> [2] https://review.openstack.org/#/c/114437/
>
> [3] http://manpages.ubuntu.com/manpages/oneiric/man8/ndsend.8.html
>
> Thanks,
> Xu Han
>
>
>
> -Anthony
>
>
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