[strongSwan] Help with DHCP-module

Dusan Ilic dusan at comhem.se
Thu Aug 10 19:22:15 CEST 2017

Hello list,

I have an issue, I have several WAN-interfaces on my linux gateway but 
only want to use one for IPsec. So I want to use "interfaces_use" 
setting in strongswan.conf and only put one WAN interface, by default 
Strongswan listens on all interfaces/IP's (even local LAN interfaces, in 
my case different LAN-bridges). The reason I want to do this is because 
I don't want the server to propose to a remote client with MOBIKE all 
IP-adresses it posseses (absolutely not local LAN IP's), because what 
happens is if I'm on 3/4G and connected to the gateway in Android, then 
roam over to local Wifi (where the gateway is) it will propose ie to the Android client, and then it keeps a tunnel when actually 
connected locally to the same LAN and gateway.

So by using "interfaces_use" I solve this, however this also seem to 
introduce a problem with the DHCP-plugin. It seems like when I restrict 
Strongswan to only one WAN-interface, the plugin stops working because 
the DHCP server is on the same gateway locally on br0 interface (

Is there a way working around this somehow?
So what I want is for Strongswan only listening on and presenting one 
WAN-interface public IP, while still letting the DHCP-module aquire an 
IP from the local DHCP-server on the same gateway. Below is my current 
DHCP-plugin settings, these work as expected until I introduce 
"interface_use" in strongswan.conf.

         dhcp {
             # Always use the configured server address.
             force_server_address = yes

             # Derive user-defined MAC address from hash of IKE identity.
              identity_lease = yes

             # Interface name the plugin uses for address allocation.
             interface = br0

             # Whether to load the plugin. Can also be an integer to 
increase the
             # priority of this plugin.
             load = yes

             # DHCP server unicast or broadcast IP address.
            server = # (broadcast address, doesn't 
work for some reason)

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