GTP-U response outer IP address

[Suga1975]

Hi,

I'm testing GTP-U with loopback mode in v3.03.

I set the server up with
$ sudo ./t-rex-64 -i --astf --software --tso-disable --lro-disable --ipv6

The client I go through the following steps:
$ ./trex-console
trex>tunnel --type gtpu --loopback
trex>tunnels_topo load -f astf/gtpu_topo.py
trex>start -f astf/http_simple.py

gtpu_topo.py is set like this.
from trex.astf.api import *
from trex.astf.tunnels_topo import TunnelsTopo
def get_topo():
topo = TunnelsTopo()
topo.add_tunnel_ctx(
src_start = '4.0.0.0',
src_end = '4.0.0.255',
initial_teid = 0,
teid_jump = 1,
sport = 5000,
version = 6,
tunnel_type = 1,
src_ip = '2001:232:1002:51::1',
dst_ip = '3001:db8:3:4::1',
activate = True
)
return topo

Then, I found that traffic from src to dst port went as expected.
However, response traffic from dst to src port might not be generated properly.

src/dst outer IP addresses in outbaund traffic are set like this as expected.
src outer IP: 2001:232:1002:51::1
dst outer IP: 3001:db8:3:4::1

src/dst outer IP addresses in inbound traffic are set like this. (same IP addresses as outbound packet)
src outer IP: 2001:232:1002:51::1
dst outer IP: 3001:db8:3:4::1

I thinks src/dst outer IP addresses should be flipped in inbound traffic.
Otherwise, the packet never reaches src port.

Is this an expected behavior?

Captured test traffic.
tx0.pcap: tx traffic capture in src port
tx1.pcap: tx traffic capture in dst port
pcap.zip