Hi Joost, > Does anybody knows what this message means?
Literally what it says. The client requests an unknown configuration attribute. Attribute 25 is INTERNAL_DNS_DOMAIN, defined by draft-ietf-ipsecme-split-dns [1]. Even if the daemon currently doesn't know the attribute's name, values can still be assigned to clients via the numeric identifier (see e.g. the documentation for the attr plugin, or that of the swanctl.conf pool sections). Regards, Tobias [1] https://tools.ietf.org/html/draft-ietf-ipsecme-split-dns
