Hello,

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

What do you think?

Emeric

----- Mail original -----
De: "Emeric POUPON" <emeric.pou...@stormshield.eu>
À: "FreeBSD Net" <freebsd-net@freebsd.org>
Envoyé: Lundi 17 Août 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=markup#l971

When I set the net.key.preferred_oldsa to 0 (similar to Linux's behavior, 
according 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 "second" 
of time?

strongSwan does not expect that behavior and I can see a lot of errors in its 
logs: the SA has been deleted but it does not know about that (strongSwan wants 
to control the SA installation/deletion itself).
Two pairs of SA may be negotiated and installed at the same time due to high 
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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