[strongSwan] StrongSwan using Loopback IP address

[Patrick Velder]

Hi

I'm operating a setup running BGP with a configured loopback: 
185.117.xx.254.
As the loopback IP is reachable over all upstreams / peers / 
downstreams, I'd like to use this IP as "leftsourceip":

Config:

>
> conn %default
>   keyexchange=ikev1
>   ikelifetime=86400s
>   ike=aes256-sha512-modp4096!
>   esp=aes256-sha512-modp1024!
>   lifetime=1800s
>   auto=start
>   aggressive=no
>
> conn cr1-home
>   left=185.117.xx.254
>   right=84.75.xx.133
>   authby=pubkey
>   leftrsasigkey=/etc/ipsec.d/public/xx.pem
>   rightrsasigkey=/etc/ipsec.d/public/yy.pem
>   dpdaction=restart
>   dpddelay=10s
>   dpdtimeout=60s
>
> # Transport GRE
> conn cr1-home-gre
>   also=cr1-home
>   type=transport
>   leftprotoport=gre
>   rightprotoport=gre
>
> # Monitoring <-> Home
> conn cr1-home-monitoring
>   also=cr1-home
>   type=tunnel
>   leftsubnet=185.117.xx.64/29
>   rightsubnet=10.0.0.0/20
>
Now the problem is that StrongSwan tries to add a route for 
"10.0.0.0/20" (rightsubnet) to "my transit's nexthop" (185.95.xxx.41) 
via the "loopback interface" (dummy0), which of course fails as there is 
only one /32 configured on the loopback interface:

> Jan 14 22:07:12 cr1 charon: 07[KNL] using 185.95.xx.41 as nexthop to 
> reach 84.75.xx.133/32
> Jan 14 22:07:12 cr1 charon: 07[KNL] installing route: 10.0.0.0/20 via 
> 185.95.xx.41 src 185.117.xx.65 dev dummy0
> Jan 14 22:07:12 cr1 charon: 07[KNL] unable to install source route for 
> 185.117.xx.65

Is there a way to fix that?

Regards
Patrick