netdev - Re: ipv6 issues after an DDoS for kernel 4.6.3

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Date:	Fri, 08 Jul 2016 16:14:20 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Toralf Förster <toralf.foerster@....de>
Cc:	netdev@...r.kernel.org
Subject: Re: ipv6 issues after an DDoS for kernel 4.6.3

On Fri, 2016-07-08 at 15:51 +0200, Toralf Förster wrote:
> I do run a 4.6.3 hardened Gentoo kernel at a commodity i7 server. A
> DDoS with about 300 MBit/sec over 5 mins resulted an issue for ipv6 at
> that system.
> 
> The IPv6 monitoring from my ISP told my that the to be monitored
> services (80, 443, 52222) weren't reachable any longer at ipv6 (at
> ipv4 there was no issue). Restarting the NIC brought back green lights
> for the services at the ipv6 ports too.

Hard to tell without knowing DDOS details, but IPv6 lacks some
scalability improvements found in IPv4.

IPv4 no longer has a routing cache, but IPv6 still has one.

Are you sure conntrack is needed at all ?