In this slide, we discuss the concept of IPTABLES/EBTABLES and then show how they work in a simple docker environment. In order to track the packet flow in those containers communication, we use the LOG module in IPTABLES/EBTABLE to track the information.

1. IPTABLES (I)
HungWei Chiu

2. HungWei Chiu
•MTS @ ONF
•SDNDS-TW/CNTUG
•Linux/Network/Container/
Kubernetes
•Kuberentes Courses @Hiskio

3. Why IPTABLES

4. IPTABLES Series
Introduction to IPTABLES
Learn IPTABLES by Docker environment.
Implementation of IPTABLES
User Space/Kernel Space
Implement our own iptables modules
Kubernetes Service discussion
Layer4 load-balancing, why ?
Modify the kernel module to make it support Layer7, really ?

5. Today

6. Environment
ContainerA ContainerA
Linux Bridge
Eth0
Eth0 Eth0
Veth0 Veth1
Host to Container
Container to
Container
Container to WAN

7. Architecture
iptables
iptables-save
Iptables-xxxx

8. IPTABLES/EBTABLES
Example
iptables -t nat -A OUTPUT ! -d 127.0.0.0/8 -m addrtype --dst-type LOCAL -j DOCKER
ebtables -t filter -I INPUT --log --log-prefix 'ctc/ebtable/filter-input' --log-level debug
Components
Chain. -> Insert/Append (-I/-A)
Table
Match (Module) -> build-in/module
Target (Module). -> build-in/module

9. Chain (EBTABLES)
INPUT
Frames destined for the bridge
itself
FORWARD
Frames being forwarded by the
bridges
OUTPUT
Locally-generated
Routed frames
PREROUTING (PREFORWARDING)
Altering frames as soon as they come
in
POSTROUTING (POSTFORWARDING)
Altering frames as they are about to
go out
BROUTING
Traversed very early, route or bridge
frame.

10. Tables (EBTABLES)
Filter
Filter frames
NAT
Change the MAC Address
broute
Make the decision (bridge/route)

11. DNAT
DNAT SNAT
SNAT
ContainerA ContainerA
Linux Bridge
Eth0 Eth0
Veth0 Veth1

12. Observe Flows
We use the target LOG to log the packet information and then learn the
packer flow in different situation.
ebtables -t broute -I BROUTING --log --log-prefix 'ctc/ebtable/
broute-BROUTING' --log-level debug
We focus on
Host to container
Container to container

13. Container to Container

14. Scripts
Setup ebtables rules
./ebtables.sh
Modify kernel module
Add printk(....)
Need to rebuild the kernel module and re-install
Generate traffic to container.
sudo dmesg -c (clean buffer)
sudo docker exec netutils ping 172.18.0.2 -c1
sudo dmesg -c

15. Container to Container

17. Host to Container

18. Scripts
Setup ebtables rules
./ebtables.sh
Modify kernel module
Add printk(....)
Need to rebuild the kernel module and re-install
Generate traffic to container.
sudo dmesg -c (clean buffer)
sudo ping 172.18.0.2 -c1
sudo dmesg -c

19. Host to Container
PING

20. Host to Container
PING

21. Before IPTABLES

22. Example (docker -p)
Iperf server
Linux Bridge
172.17.8.111
172.18.0.4
Veth0
MacBook
VM
172.17.8.1
Iperf client
In Virtual Machine
docker run -d --name iperf -p 12345:5201 --entrypoint iperf3 hwchiu/
netutils -s -p 5201
In MAC
iperf3 -c 172.17.8.111 12345
Iptables will do DNAT to redirect packets
iptables-save -t nat -c
-A DOCKER ! -i docker0 -p tcp -m tcp --dport 12345 -j DNAT --to-
destination 172.18.0.4:5201

23. Conntrack
Connection Tracking
Connection-> application level.
Track the connection:
Request tuple -> Replay tuple
Tuple: src_ip, dest_ip, src_port, dest_port

24. Conntrack
Iperf server
Linux Bridge
172.17.8.111
172.18.0.4
Veth0
MacBook
VM
172.17.8.1
Iperf client
Request tuple
172.17.8.1:53426 -> 172.17.8.111:12345
Reply
172.18.0.4:5201 -> 172.17.8.1:53426
Iptables do NAT only once and then conntrack handles the rest of
packets.

25. Tables (IBTABLES)
Raw
For non-tracking packets. (Before conntrack)
Mangle
Change packet's information
Filter
Filter packets
NAT
Change IP address (SNAT/DNAT)

26. Chain (IPTABLES)
INPUT
Packets destined to local
sockets
FORWARD
Packets being routed
OUTPUT
Locally-generated packets
PREROUTING
Altering packets as soon as
they come in
POSTROUTING
Altering packets as they
are about to go out

27. DNAT
DNAT
SNAT
SNAT

28. Others
http://xkr47.outerspace.dyndns.org/netfilter/packet_flow/packet_flow10.png

29. Observe Flows
We use the target LOG to log the packet information and then learn the packer flow in
different situation.
iptables -t mangle -I PREROUTING -p tcp -d 172.18.0.0/16 -j LOG --log-prefix '/
iptable/mangle-PREROUTE' --log-level debug
We focus on
Container to container
Host to container
WAN to container

30. Container to Container

31. Scripts
Setup ebtables rules
./ebtables.sh
./iptables.sh
Generate traffic to container.
sudo dmesg -c (clean buffer):
sudo docker exec netutils ping 172.18.0.2 -c 1
sudo dmesg -c > test

32. Container to Container

33. No NAT in Reply Packet

34. Have You Seen This?
sudo sysctl net.bridge.bridge-nf-call-iptables=1
echo '1' > /proc/sys/net/bridge/bridge-nf-call-iptables
Try to repeat this case with value '0'

35. Host to Container

36. Scripts
Setup ebtables rules
./ebtables.sh
./iptables.sh
Generate traffic to container.
sudo dmesg -c (clean buffer):
ping 172.18.0.2 -c 1
sudo dmesg -c > test

37. ICMP Request to Container
PING

38. ICMP Reply From Container
PING

39. Others
What is Bridge Check?
Different Function Handler
netdev_rx_handler_register
br_handle_frame

40. WAN to Container

41. Scripts
Setup ebtables rules
./ebtables.sh
./iptables.sh
Generate traffic to container.
sudo dmesg -c (clean buffer):
sudo docker exec netutils ping 8.8.8.8 -c 1
sudo dmesg -c > test

42. ICMP Request to WAN
PING

43. ICMP Reply From WAN
PING

44. Tcpdump

45. How To Debug
No Simple Way
Strong knowledge of TCP/IP
Capture Packets by TCPDUMP
Check IPTables rules
Use the log module to capture packets (watch out match rules).
Check other build-in services.
ARPTables
Routing Tables
TC (Traffic Shaping)
Modify the Linux Kernel to print out packet information.

46. Q&A