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Re: IPSEC: on behavior of acquire

To: hadi@xxxxxxxxxx
Subject: Re: IPSEC: on behavior of acquire
From: Aidas Kasparas <a.kasparas@xxxxxx>
Date: Sat, 02 Apr 2005 10:10:05 +0300
Cc: ipsec-tools-devel@xxxxxxxxxxxxxxxxxxxxx, netdev@xxxxxxxxxxx, nakam@xxxxxxxxxxxxxx
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jamal wrote:
test1)on one window run setkey -x:

ping -c 1 someDST

-1) packet arrives towards outbound
0) Larval state created
1) one acquire sent.
2) timeout.
3) packet dropped. -ESRCH returned.
4) larval state deleted

So question 1): Shouldnt the return code be -ERESTART to ask
the app to retry?
question 2) Why is there a hardcoding of 1 try only?

Re 1 try only. There is little sense to do more tries. If there is no deamon listening to pfkey messages, then no connection will be made no matter how many retries you'll do. If deamon/link/peer is slow and SA was not established before timeout expired, then repeated acquire will be simply ignored (deamon will find out that negotiation is already in progress, there is no reason to start another negotiation and therefore will drop that acquire request). And the only situation where repeated acquires may help is when pfkey messages are lost. But pfkey was not designed to survive message loses, therefore you should not operate your boxes in mode when lost pfkey messages are a rule, not an exception. And on the other hand, occasional pfkey message loses can be worked around by applications/user retry.

Re error code returned. Error codes returned by pfkey never were perfect. But your experiment is not perfect too. You sent pings with no KE deamon running. pfkey code found that there is nothing receiving acquire messages => there is no chance that any process will setup required SAs and tried to inform about that (I agree, return code is not very informative, at least until you learn about reasons why it is such). If you would have racoon (or other pfkey based ISAKMP daemon) running, you would get "resource temporarily unavailable" (don't know which error code corresponds to that message), which IMHO is ok (if it is not, please explain).

Re netlink behaviour I can not comment as I don't use it for ipsec purposes, but would like to read similar explanation. Reason for that - idea that ipsec-tools one day could support operation via netlink is not ruled out of our minds. Yet, afaik nobody is working on it at the moment.

Aidas Kasparas
IT administrator
GM Consult Group, UAB

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