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Date:      Mon, 28 Sep 2015 10:08:25 +0200 (CEST)
From:      Emeric POUPON <emeric.poupon@stormshield.eu>
To:        FreeBSD Net <freebsd-net@freebsd.org>
Subject:   Re: IPsec: question on the sysctl preferred_oldsa
Message-ID:  <1049417046.2997430.1443427705821.JavaMail.zimbra@stormshield.eu>
In-Reply-To: <868621474.11105551.1439798865541.JavaMail.zimbra@stormshield.eu>
References:  <868621474.11105551.1439798865541.JavaMail.zimbra@stormshield.eu>

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Hello,

No idea on this question?
To sum up the potential problems:
- strongSwan does not expect the kernel to destroy a SA, and produces error=
s after that (it cannot find the expected SA in the kernel since it has bee=
n deleted)
- racoon uses the "delete" event from the kernel and creates a ISAKMP DELET=
E message to the remote host, with the relevant SPI. In some situations, bo=
th endpoints negotiate a pair of SA at the same time, and keep deleting the=
ir old SA and renegotiate. I suspect this behavior to be related to this sy=
sctl.

What do you think?

Emeric

----- Mail original -----
De: "Emeric POUPON" <emeric.poupon@stormshield.eu>
=C3=80: "FreeBSD Net" <freebsd-net@freebsd.org>
Envoy=C3=A9: Lundi 17 Ao=C3=BBt 2015 10:07:45
Objet: IPsec: question on the sysctl preferred_oldsa

Hello,

I have some questions about the sysctl "net.key.preferred_oldsa":
https://svnweb.freebsd.org/base/head/sys/netipsec/key.c?view=3Dmarkup#l971

When I set the net.key.preferred_oldsa to 0 (similar to Linux's behavior, a=
ccording to what I have read so far):
- why does the kernel delete itself the old SA ? Why not just selecting the=
 newest one?
- why does it delete the old SA only if it has been created in another "sec=
ond" of time?

strongSwan does not expect that behavior and I can see a lot of errors in i=
ts logs: the SA has been deleted but it does not know about that (strongSwa=
n wants to control the SA installation/deletion itself).
Two pairs of SA may be negotiated and installed at the same time due to hig=
h load, bidirectional traffic. It seems to be quite questionable to delete =
the old one in that case.

What do you think?

Emeric
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