VPN configuration 
 
vpn {
      ipsec {
          copy-tos disable
          ipsec-interfaces {
              interface eth0
          }
          nat-networks {
              allowed-network 10.0.88.0/24 {
              }
          }
          nat-traversal enable
      }
      l2tp {
          remote-access {
              authentication {
                  local-users {
                      username me {
                          password me                      }
                  }
                  mode local
              }
              client-ip-pool {
                  start 192.168.1.100
                  stop 192.168.1.110
              }
              ipsec-settings {
                  authentication {
                      mode pre-shared-secret
                      pre-shared-secret me                   }
              }
              outside-address 10.0.88.10
              outside-nexthop 10.0.88.1
          }
      }
  }