[strongSwan] 5.0.1 unable to set UDP_ENCAP: Protocol not available

[Nan Luo]

Hello, all

I was trying to setup a IPv6 tunnel with strongSwan as the client. strongSwan sent the IKE_SA_INIT  to my SGW and the SGW  properly responded. Wireshark capture indicated that the IKE_SA_INIT response was received on the network interface that strongSwan was listening on, however the packet (IKE_SA_INIT response) was not handed over to charon, instead the packet was responded with a "ICMPv6 Unreachable (Administratively prohibited)".  Any idea that the linux kernel can fail to distribute the packet to charon?  

Examing the charon logs, I found the following errors:
"
charon: 00[KNL] unable to set UDP_ENCAP: Protocol not available
charon: 00[NET] enabling UDP decapsulation for IPv6 on port 4500 failed
"

Do those errors have anything to do with the failure to setup IPv6 tunnels? 

I am currently running strongSwan 5.0.1. The IPv6 connection is:
conn ipv6_cert
    left=1080::192:160:1:100
    leftsourceip=%config
    leftcert=ss.cert
    leftauth=pubkey
    leftsubnet=1080::6:0:0/112
    leftfirewall=yes
    rightfirewall=yes
    right=1080::192:160:1:10
    rightsubnet=1080::15:15:15:0/112
    rightauth=pubkey
    auto=add
    esp=aes-sha1-md5-modp1024
    ike=3des-aes-sha1-md5-modp1024


-----------------
Thanks for your help


Nan
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