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Chapter 28. Configuring Native Container Routing
28.1. Network Overview
The following describes a general network setup:
- 11.11.0.0/16 is the container network.
- The 11.11.x.0/24 subnet is reserved for each node and assigned to the Docker Linux bridge.
- Each node has a route to the router for reaching anything in the 11.11.0.0/16 range, except the local subnet.
- The router has routes for each node, so it can be directed to the right node.
- Existing nodes do not need any changes when new nodes are added, unless the network topology is modified.
- IP forwarding is enabled on each node.
The following diagram shows the container networking setup described in this topic. It uses one Linux node with two network interface cards serving as a router, two switches, and three nodes connected to these switches.
![Network Diagram](https://access.redhat.com/webassets/avalon/d/OpenShift_Container_Platform-3.7-Installation_and_Configuration-en-US/images/28871ce4cf4a4b40005b712659d28308/network_diagram.png)
28.2. Configure Native Container Routing
You can set up container networking using existing switches and routers, and the kernel networking stack in Linux.
As a network administrator, you must modify, or create a script to modify, the router or routers when new nodes are added to the cluster.
You can adapt this process to use with any type of router.
28.3. Setting up a Node for Container Networking
Assign an unused 11.11.x.0/24 subnet IP address to the Linux bridge on the node:
# brctl addbr lbr0 # ip addr add 11.11.1.1/24 dev lbr0 # ip link set dev lbr0 up
Modify the Docker startup script to use the new bridge. By default, the startup script is the
/etc/sysconfig/docker
file:# docker -d -b lbr0 --other-options
Add a route to the router for the 11.11.0.0/16 network:
# ip route add 11.11.0.0/16 via 192.168.2.2 dev p3p1
Enable IP forwarding on the node:
# sysctl -w net.ipv4.ip_forward=1
28.4. Setting up a Router for Container Networking
The following procedure assumes a Linux box with multiple NICs is used as a router. Modify the steps as required to use the syntax for a particular router:
Enable IP forwarding on the router:
# sysctl -w net.ipv4.ip_forward=1
Add a route for each node added to the cluster:
# ip route add <node_subnet> via <node_ip_address> dev <interface through which node is L2 accessible> # ip route add 11.11.1.0/24 via 192.168.2.1 dev p3p1 # ip route add 11.11.2.0/24 via 192.168.3.3 dev p3p2 # ip route add 11.11.3.0/24 via 192.168.3.4 dev p3p2