netdev - Re: [PATCH net-next v2 0/2] net: ipv6: Improve user experience with multipath routes

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Date:   Fri, 27 Jan 2017 09:36:49 -0700
From:   David Ahern <dsa@...ulusnetworks.com>
To:     nicolas.dichtel@...nd.com, David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, roopa <roopa@...ulusnetworks.com>
Subject: Re: [PATCH net-next v2 0/2] net: ipv6: Improve user experience with
 multipath routes

On 1/27/17 9:29 AM, Nicolas Dichtel wrote:
> Le 26/01/2017 à 19:00, David Miller a écrit :
>> From: David Ahern <dsa@...ulusnetworks.com>
> [snip]
>>> Quagga does not properly handle IPv6 multipath routes received from
>>> the kernel. I checked this with debian/jessie version and our
>>> version, and Donald reviewed the source. It is broken.
>>
>> If this is true, quagga is asbolutely not an argument for this "breaking"
>> something.  It doesn't break anything.
> Ok, my tests also shows that quagga is buggy.
> Let's change the way to advertise these routes.
> 
> It would be great to also use RTA_MULTIPATH when a route is deleted (like in
> your patch 1/2).

I have updated notifications to use RTA_MULTIPATH. Working on the multipath add/delete/replace permutations now and what the notification looks like. Add/replace is easy and the notifications use RTA_MULTIPATH. Notifications for the delete path are complicated given that a delete could remove only a subset of nexthops. Given that, we might have to settle for a notification for each nexthop delete.

> 
> Note that there is still a difference between ipv4 and ipv6: in ipv4 when a
> nexthop is added/updated/removed, the whole route must be deleted and added
> again. In IPv6, nexthop can be managed one by one.
> It means that in ipv4, the full route is always dumped, which is not the case in
> ipv6.
> 

Yes. I have been working on how to delete a nexthop within an IPv4 route. It is much more complicated given how the route is stored compared to IPv6.