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.
