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[24.23.181.79]) by smtp.googlemail.com with ESMTPSA id w206sm9531068pfc.1.2020.09.27.20.38.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 27 Sep 2020 20:38:29 -0700 (PDT) Subject: Re: IPv6 regression introduced by commit 3b6761d18bc11f2af2a6fc494e9026d39593f22c To: Baptiste Jonglez Cc: Alarig Le Lay , netdev@vger.kernel.org, jack@basilfillan.uk, Vincent Bernat , Oliver References: <20200305081747.tullbdlj66yf3w2w@mew.swordarmor.fr> <20200927153552.GA471334@fedic> <20200927161031.GB471334@fedic> From: David Ahern Message-ID: <66345b05-7864-ced2-7f3c-493260be39f7@gmail.com> Date: Sun, 27 Sep 2020 20:38:28 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20200927161031.GB471334@fedic> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 9/27/20 9:10 AM, Baptiste Jonglez wrote: > On 27-09-20, Baptiste Jonglez wrote: >> 1) failing IPv6 neighbours, what Alarig reported. We are seeing this >> on a full-view BGP router with rather low amount of IPv6 traffic >> (around 10-20 Mbps) > > Ok, I found a quick way to reproduce this issue: > > # for net in {1..9999}; do ip -6 route add 2001:db8:ffff:${net}::/64 via fe80::4242 dev lo; done > > and then: > > # for net in {1..9999}; do ping -c1 2001:db8:ffff:${net}::1; done > > This quickly gets to a situation where ping fails early with: > > ping: connect: Network is unreachable > > At this point, IPv6 connectivity is broken. The kernel is no longer > replying to IPv6 neighbor solicitation from other hosts on local > networks. > > When this happens, the "fib_rt_alloc" field from /proc/net/rt6_stats > is roughly equal to net.ipv6.route.max_size (a bit more in my tests). > > Interestingly, the system appears to stay in this broken state > indefinitely, even without trying to send new IPv6 traffic. The > fib_rt_alloc statistics does not decrease. > fib_rt_alloc is incremented by calls to ip6_dst_alloc. Each of your 9,999 pings is to a unique address and hence causes a dst to be allocated and the counter to be incremented. It is never decremented. That is standard operating procedure.