[Swan] Outbound traffic not going through IPSec tunnel

[Yongsheng Xie]

Hello,

Recently I am encountered with a weird problem. I have a Fedora 26 server
as virtualization host, running VMs on a Linux logical network (the
left-hand side). I've also set up a CentOS 7.3 VM on Google Cloud Platform
(the right-hand side) for establishing the IPSec tunnel.

After the tunnel established, I can ping the VM in 10.150.0.0/24 from any
GCE instances on 10.120.0.0/16, even ssh into VM from GCE instances. What's
really weird is that I cannot ping or establish connection to any hosts on
GCE VPC from the hosts on network 10.150.0.0/24. I tried using tcpdump to
capture packets flowing through IPSec tunnel, but I can't see any packets
routed from 10.150.0.0/24 to 10.120.0.0/16.

Could you help me debugging this problem?

Following is setup information of my servers:

*The setup of left-hand side:*
OS: Fedora 26
Libreswan version: 3.18
Configuration:
conn cdg-tpe
    left=X.X.X.X
    leftsubnet=10.150.0.0/24
    right=Y.Y.Y.Y # The external IP of the GCE instance
    rightid=10.120.0.2
    rightsubnet=10.120.0.0/16
    auto=start
    authby=secret

*The setup of right-hand side:*
OS: CentOS 7.3
Libreswan version: 3.15
Configuration:
conn tpe-cdg
    left=10.120.0.2
    leftsubnet=10.120.0.0/16
    right=X.X.X.X
    rightsubnet=10.150.0.0/24
    auto=start
    authby=secret


Thanks,
Yongsheng Xie
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