netdev - Re: [PATCH net-next] ipv6: implement rt_genid_bump_ipv6 with fn_sernum and remove rt6i

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Date:	Thu, 11 Sep 2014 08:22:33 -0400
From:	Vlad Yasevich <vyasevich@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	David Miller <davem@...emloft.net>
CC:	netdev@...r.kernel.org, eric.dumazet@...il.com,
	nicolas.dichtel@...nd.com
Subject: Re: [PATCH net-next] ipv6: implement rt_genid_bump_ipv6 with fn_sernum
 and remove rt6i_genid

On 09/11/2014 04:30 AM, Hannes Frederic Sowa wrote:
> On Mi, 2014-09-10 at 13:09 -0700, David Miller wrote:
>> From: Hannes Frederic Sowa <hannes@...essinduktion.org>
>> Date: Wed, 10 Sep 2014 11:31:28 +0200
>>
>>> In case we need to force the sockets to relookup the routes we now
>>> increase the fn_sernum on all fibnodes in the routing tree. This is a
>>> costly operation but should only happen if we have major routing/policy
>>> changes in the kernel (e.g. manual route adding/removal, xfrm policy
>>> changes).
>>
>> Core routers can update thousands of route updates per second, and they
>> do this via what you refer to as "manual route adding/removal".
> 
> Sorry, I was too unspecific here. Route changes because of address
> removal/addition on the local stack.
> 
> The reason why we do the bump_id here is that we want to flush all the
> socket caches in case we have either lost or gained access to a new
> source address.
> 
> If you think about e.g. BGP routers which update lots of routes, they
> aren't affected and the flush won't happen on every route change.
> 
>> I don't think we want to put such a scalability problem into the tree.
>>
>> There has to be a lightweight way to address this.
> 
> I am still investigating why this bump_id actually happened. Seems the
> reason is only sctp ontop of IPv6 and maybe we can build something much
> more lightweight, yes.

No.  It was proven that a regular TCP socket could continue sending
traffic using an address that was removed.

-vlad
> 
> Thanks,
> Hannes
> 
> 
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