[strongSwan] Missing NAT keep alive packets when forceencaps is set

[Lars Alex Pedersen]

Got a roadwarrior/client connection where NAT-T isn't auto detected. I tried to solve this by forcing UDP encapsulation using forceencaps=yes and expected that NAT keep alive packets also where sent in order to keep the connection alive. But this doesn't seem to be the case. 

Can I enable this behaviour somehow?

# /etc/ipsec.conf - strongSwan IPsec configuration file

config setup
        #charondebug="cfg 4, dmn 4, ike 4, net 4"
        charondebug="cfg 1, dmn 2, ike 1"

conn %default
        #ikelifetime
        lifetime=10800s
        margintime=600s
        rekey=yes
        reauth=no
        forceencaps=yes
        keyingtries=1
        keyexchange=ikev2
        type=tunnel
        dpdaction=clear
        dpddelay=900s
        ike=aes256gcm128-sha512-ecp512bp,aes256gcm128-sha512-ecp521!
        esp=aes256gcm128-ecp512bp,aes256gcm128-ecp521,aes128gcm128-ecp256bp!
        authby=psk

# Configuration notes:
# left = local, right = remote
# leftid/rightid: ID payload exchanged during IKE (certificate: DN or subjectAltName)
# ! in ike and esp only allow specified cypher suites (no NSA downgrade)
# TFC: Traffic Flow Confidentiality
# DPD: Dead Peer Detection
conn omnia
        left=x.x.x.x
        leftid=myid
        leftsourceip=%config
        leftfirewall=no
        right=x.x.x.x
        rightid=something
        rightsubnet=x.x.x.x/y
        tfc=1280
        auto=route

Best regards
Lars Pedersen.