[strongSwan] Connectivity between Windows 2019 server and Ubuntu 16.04 stops; can TS be explicitly specified

Tobias Brunner tobias at strongswan.org
Tue Sep 8 15:03:54 CEST 2020

Hi Karuna,

> 1. I'm only adding or removing connections in ipsec.conf and not
> modifying existing connections. And also I only use complete IP
> addresses for both left and right. So, would `ipsec update` be better
> suited and would still cause any other known issues?

Just never use `ipsec reload` unless you know why you do so.  And if you
don't modify existing connections using `ipsec update` should be fine
(however, if you remove connections, note that this does not affect
existing SAs, so you'd have to terminate those manually, before or after
removing the config).

> 2. Yes I looked at left|rightsubnet and I don't want to restrict
> protocol/port rather would like to apply to all protocol and all ports.
> And if I understand correctly, the default values for left|rightsubnet
> is all protocol and all port. Correct?

Yes, by default all traffic between the local and remote IP addresses
will be covered.

> 3. The charon.ignore_acquire_ts would apply to outbound traffic correct?
> From what I understand (based on below logs), the issue occurs on
> the inbound traffic, strongswan is not accepting the remote TS? Because
> the left|rightsubnet is not configured i.e. default values, so shouldn't
> it be accepting every remote TS?

Yes, the option applies when outbound traffic hits a trap policy and the
kernel triggers an acquire.  And no, the daemon won't accept just any
TS, only a TS that matches the local and remote IPs is accepted if you
don't configure any traffic selectors.  Since this apparently is the
case here (according to the log), the problem is probably caused by
`ipsec reload` (i.e. there simply is no child config to match the
received traffic selectors against).

> 4. Or would TSi and TSr need to match for the CREATE_CHILD_SA to be
> successful? In which case, TS_UNACCEPT can happen on both inbound and
> outbound traffic? I guess, I'm asking under what circumstances
> TS_UNACCEPT error is seen?

Simply when there is no config with matching TS (could have different

> 4. Would strongswan.conf work along with ipsec.conf/starter?

strongswan.conf contains global settings, which apply to all daemons and
config backends.  You may mix config backends (e.g. swanctl.conf/vici
and ipsec.conf/starter) but I'd not recommend that unless you know
exactly what you are doing.  So either use one or the other.  It's fine
to start the daemon via starter for either of them, though (when using
swanctl, just leave ipsec.conf/ipsec.secrets and the directories under
ipsec.d empty).


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