No packets sending through 6lowpan

Start by reproducing the TCP failure on the Raspberry Pi Zero W setup using the bluetooth_6lowpan module, bt0, and the provided Python client and server. Compare the working ping traffic with the missing application packets using tshark, while checking the reported Linux 5.10.17+ environment. Done means TCP data can traverse the 6lowpan interface as expected.

Describe the bug
Connected two Raspberry Pi W using 6lowpan and ping is working fine with global address at both devices. However, it seems that no programs can send data through the interface, I tried python scrips and mosquitto server etc.

To reproduce

Client:

Enable bluetooth_6lowpan module

modprobe bluetooth_6lowpan
echo 1 > /sys/kernel/debug/bluetooth/6lowpan_enable

Start advertising

hciconfig hci0 leadv

Server:

modprobe bluetooth_6lowpan
echo 1 > /sys/kernel/debug/bluetooth/6lowpan_enable
hcitool lescan

Connect to the client with the bluetooth mac address discovered

echo "connect <mac addr> 1" > /sys/kernel/debug/bluetooth/6lowpan_control

Ping with link local address

ping6 -I bt0 <link local address of the client>

Add gloabal address (in client)

ip addr add fd00::2/64 dev bt0

Add global address (in server)

ip addr add fd00::1/64 dev bt0

Ping the global address, server to client, works fine

ping6 fd00::2

Ping the global address, client to server, works fine

ping6 fd00::1

Try to connect client to server using a program, such as python scripts given below, No data is sending through the 6lowpan (observe with a tshark, or similar).

tcp client program

#!/usr/bin/env python3

import socket
import struct

SERVER_ADDR = 'fd00::1'
SERVER_PORT = 9001
sequence_number = 1
sock = socket.socket(socket.AF_INET6, socket.SOCK_STREAM)
print('send connect request')
sock.connect((SERVER_ADDR, SERVER_PORT))

while sequence_number < 101 :
data = struct.pack("!I", sequence_number)
data += 'Ping'
sock.sendto(data, (SERVER_ADDR, SERVER_PORT, 0, 0))
recv_data = sock.recvfrom(8)
print(recv_data)
sequence_number+= 1

sock.close()
del sock

tcp server program

#!/usr/bin/env python3

import socket

SERVER_ADDR = ''
SERVER_PORT = 9001

with socket.socket(socket.AF_INET6, socket.SOCK_STREAM) as s:
server_addr = (SERVER_ADDR, SERVER_PORT, 0, 0)
s.bind(server_addr)
s.listen(1)
conn, addr = s.accept()
with conn:
while True:
data = conn.recv(128)
if not data:
print('break')
break
conn.sendall(data)
s.close()
del s

System

• Which model of Raspberry Pi?
  PiZeroW

• Which OS and version (cat /etc/rpi-issue)?
  Raspberry Pi reference 2020-12-02
  Generated using pi-gen, https://github.com/RPi-Distro/pi-gen, cce27bd6f44a3b2e83855645986b3e21f771e852, stage2

• Which firmware version (vcgencmd version)?
  Feb 25 2021 12:12:09
  Copyright (c) 2012 Broadcom
  version 564e5f9b852b23a330b1764bcf0b2d022a20afd0 (clean) (release) (start)

• Which kernel version (uname -a)?
  Linux raspberrypi 5.10.17+ #1403 Mon Feb 22 11:26:13 GMT 2021 armv6l GNU/Linux