This presentation covers in details about Docker Networking

1. Docker Networking
Kingston Smiler. S (kingstonsmiler@gmail.com)

2. Agenda
 Introduction and Key Concepts
 Docker Communication requirement
 Different methods of Docker networking
 Sample Setup
 Limitation of current Docker Networking

3. Docker Networking - Introduction
Concept Description
Network Namespace Provide a way of having separate network stack for each
instance of a container.
Docker0 Bridge Default bridge created by docker to provide communication
across docker containers and external world including the
host.
Port Mapping Mechanism to map a port in the host machine with the
Docker container’s networking stack.
Veth Pair Veth is a special, logical, virtual interface which is similar to a
link / pipe. It has two ends which are logical interfaces and
provide connectivity across two different network elements.

4. Different Communication Requirement
 Container – Container
Communication
 Container to Host Communication
 Container to External world
communication.
 Container - Container
communication across containers
running in different host.
Cont 1 Cont 2 Cont 3
Docker0/OVS Port Map
Host1
etho

5. Different Methods of Docker Networking
 Docker Bridging
 Host Port Binding to Docker
 Docker network using host network stack (--net=host)
 Docker communication using –net=container
 Docker Container linking using –link option
 Docker Networking Using OVS (Advanced)

6. Docker Bridging
 Docker0 bridge
 Virtual bridge similar to linux
bridge
 Created in the host machine
during the creation of Docker
container.
 Veth Pair
 Will be created during the
creation of Docker container.
 One end of the veth pair is
attached to the eth0 interface
of Docker container
 Another end is attached to the
docker0 bridge with interface
name starts with vethc3cd.

7. Host Port Binding To Docker Container
 In this method, a port in the host machine will be bound to a port
in Docker.
 Simple way of running a service in Docker container and exposing
the service to external world.
 Example case is, running a webserver in the docker container and
forwarding all the web traffic which is coming to the HTTP port in
host machine to Docker container.
 -p IP:host_port:container_port option does it.
 /usr/bin/docker run -d --name port_forward -p 80:80 ubuntu_apache
/usr/sbin/apache2ctl -D FOREGROUND
 This operation is similar to NAT.
 Two or more container won’t be able to provide the same service
on same host port.

8. Docker Network Using Host Network Stack
 Docker container can use the host machines networking stack
instead of having a separate network stack.
 One way of making containers talk to external world.
 --net=host option does it
 /usr/bin/docker run -d --name h1 --net=host ubuntu_ftp vsftpd
 If two containers in the host system prefers to use this
mechanism then, port collision across the container happens.

9. Docker Communication Using Other Docker’s Network Stack
 Simple way of making containers talk to each other.
 Uses other Docker’s networking stack instead of having a
separate network stack.
 Similar to –net=host option. But here instead of using the host
machines network stack, it uses some other Docker’s network
stack.
 The two containers can talk to each other by using loopback
interface.
 --net=host option does it
 /usr/bin/docker run -d --name cont_net1 --net=container:b1 ubuntu /bin/sh -c "while
true; do echo Hello World; sleep 1; done"

10. Docker Communication Using Link
 Provides a mechanism for Docker container to transfer
information from one container to another securely.
 No ports are explicitly exposed to the destination container by
source.
 Unidirectional Conduit / Pipe between source and destination
container.
 Information about the service which is running in the source
container will be exposed to the destination.
 Simple way of providing service chaining in docker environment.
making containers talk to each other.
 docker run -d -P --name link_dest --link port_forward:link1 ubuntu /bin/sh -c "while true;
do echo Hello World; sleep 1; done"

11. Requirement Vs Communication Methods
 Container – Container Communication
 Docker0 bridge (Cont1 – Cont2 via Docker0)
 Container networking using –net=container option
(Cont4 – Cont5)
 UDS / pipe (Cont1 – Cont2)
 Container linking using –link option
 OVS (Cont1 – Cont2 via OVS)
 Container to Host Communication
 Host networking using –net=host option (Cont6)
 Docker0 bridge (Cont1, Cont2, Cont4)
 Container to External world communication.
 Port Mapping (Cont 3)
 Host networking using –net=host option (Cont 6)
 Container - Container communication across
containers running in different host.
 OVS
Cont 4 Cont 5
Cont 6
Docker0/OVS Host
Network
Host 2
Cont 1 Cont 2 Cont 3
Docker0/OVS Port Map
Host1
Veth Pair
UDS / Pipe
GRE / VXLAN Tunnel
Port Map
--net=host option
--net = container option
Eth 1
Eth 1

12. Sample Setup
b1
Host Network Stack
Host VM Machine
b2
Link
dest
h1
Port
forward
Cont
net1
enp0s3 enp0s8
Docker0/OVS

13. Thank you
kingstonsmiler@gmail.com