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Date:      Wed, 24 May 2017 12:17:50 +0200
From:      William Gathoye <william@gathoye.be>
To:        Alarig Le Lay <alarig@swordarmor.fr>
Cc:        "Andrey V. Elsukov" <bu7cher@yandex.ru>, freebsd-net@freebsd.org
Subject:   Re: Public IPv6s fail on KVM bridge with "No buffer space available"
Message-ID:  <19651499-409c-297f-9d53-fa0eeb9cdd25@gathoye.be>
In-Reply-To: <20170522121318.2pzqt5ryisrl44rn@mew.swordarmor.fr>
References:  <fbfe1ff2-bd66-9a98-d56b-6d75265936bd@gathoye.be> <84cecdc7-e331-d3bc-3fb3-e35507e231d6@yandex.ru> <a44fa8c5-d48f-25eb-51d2-16d100ba5f53@gathoye.be> <20170522121318.2pzqt5ryisrl44rn@mew.swordarmor.fr>

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From: William Gathoye <william@gathoye.be>
To: Alarig Le Lay <alarig@swordarmor.fr>
Cc: "Andrey V. Elsukov" <bu7cher@yandex.ru>, freebsd-net@freebsd.org
Message-ID: <19651499-409c-297f-9d53-fa0eeb9cdd25@gathoye.be>
Subject: Re: Public IPv6s fail on KVM bridge with "No buffer space available"
References: <fbfe1ff2-bd66-9a98-d56b-6d75265936bd@gathoye.be>
 <84cecdc7-e331-d3bc-3fb3-e35507e231d6@yandex.ru>
 <a44fa8c5-d48f-25eb-51d2-16d100ba5f53@gathoye.be>
 <20170522121318.2pzqt5ryisrl44rn@mew.swordarmor.fr>
In-Reply-To: <20170522121318.2pzqt5ryisrl44rn@mew.swordarmor.fr>

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On 05/22/2017 02:13 PM, Alarig Le Lay wrote:
> You can try to ping6 the IPv6 multicast address for all the routers on
> the link:
>=20
> 14:07 alarig@mew ~ % ping6 -c1 ff02::2%vtnet0
> PING6(56=3D40+8+8 bytes) fe80::a800:ff:fe93:83a3%vtnet0 --> ff02::2%vtn=
et0
> 16 bytes from fe80::209%vtnet0, icmp_seq=3D0 hlim=3D64 time=3D0.237 ms
>=20
> --- ff02::2%vtnet0 ping6 statistics ---
> 1 packets transmitted, 1 packets received, 0.0% packet loss
> round-trip min/avg/max/std-dev =3D 0.237/0.237/0.237/0.000 ms

In this use case, you make the assumption that my gateway is actually
the first one to respond, this is why you select only the first answer
using -c1. But as you can see below, if I remove that argument, several
routers are answering to me (seems sensible to me), how can I be sure my
gateway is actually the first device that answers?

PING6(56=3D40+8+8 bytes) fe80::ff:fec2:e61d%vtnet0 --> ff02::2%vtnet0
16 bytes from fe80::268a:7ff:fe91:e970%vtnet0, icmp_seq=3D0 hlim=3D64
time=3D0.292 ms
16 bytes from fe80::268a:7ff:fe91:ea98%vtnet0, icmp_seq=3D0 hlim=3D64
time=3D0.355 ms(DUP!)
16 bytes from fe80::2ff:ffff:feff:fffd%vtnet0, icmp_seq=3D0 hlim=3D64
time=3D2.970 ms(DUP!)
16 bytes from fe80::2ff:ffff:feff:fffe%vtnet0, icmp_seq=3D0 hlim=3D64
time=3D5.964 ms(DUP!)
16 bytes from fe80::268a:7ff:fe91:e970%vtnet0, icmp_seq=3D1 hlim=3D64
time=3D0.314 ms
16 bytes from fe80::268a:7ff:fe91:ea98%vtnet0, icmp_seq=3D1 hlim=3D64
time=3D0.389 ms(DUP!)
16 bytes from fe80::2ff:ffff:feff:fffd%vtnet0, icmp_seq=3D1 hlim=3D64
time=3D3.222 ms(DUP!)
16 bytes from fe80::2ff:ffff:feff:fffe%vtnet0, icmp_seq=3D1 hlim=3D64
time=3D6.382 ms(DUP!)

How can I understand the "DUP!" statement here? I assume these are due
because we are using multicast here end the ICMP reply are echoes to
each others? Right?

>=20
> But, it=E2=80=99s possible that you don=E2=80=99t get any reply if they=
 do some nasty
> things on their network (as Hetzner does). In that case, you=E2=80=99re=
 stuck on
> the /56 setup.
>=20

As you can see, it seems there is no restriction / too nasty things at
OVH, as I have got replies, at least :)

Regards,

--
William Gathoye
<william@gathoye.be>


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