IP Addresses, Routes and Networks
Weave Net runs containers on a private network, which means that IP addresses are isolated from the rest of the Internet, and that you don’t have to worry about addresses clashing.
You can of course also manually change the IP of any given container or subnet on a Weave network. See, How to Manually Specify IP Addresses and Subnets
Some Definitions
- IP is the Internet Protocol, the fundamental basis of network communication between billions of connected devices.
- The IP address is (for most purposes) the four numbers separated
by dots, like
192.168.48.12. Each number is one byte in size, so can be between 0 and 255. - Each IP address lives on a Network, which is some set of those
addresses that all know how talk to each other. The network address
is some prefix of the IP address, like
192.168.48. To show which part of the address is the network, we append a slash and then the number of bits in the network prefix, like/24. - A route is an instruction for how to deal with traffic destined for somewhere else - it specifies a Network, and a way to talk to that network. Every device using IP has a table of routes, so for any destination address it looks up that table, finds the right route, and sends it in the direction indicated.
IP Address Notation in Weave
In the IP address 10.4.2.6/8, the network prefix is the first 8 bits
- 10. Written out in full, that network is 10.0.0.0/8.
The most common prefix lengths are 8, 16 and 24, but there is nothing
stopping you using a /9 network or a /26. For example, 6.250.3.1/9 is on the
6.128.0.0/9 network.
Several websites offer calculators to decode this kind of address, see, for example: IP Address Guide.
The following is an example route table for a container that is attached to a Weave network:
# ip route show
default via 172.17.42.1 dev eth0
10.2.2.0/24 dev ethwe proto kernel scope link src 10.2.2.1
172.17.0.0/16 dev eth0 proto kernel scope link src 172.17.0.170
It has two interfaces: one that Docker gave it called eth0, and one
that weave gave it called ethwe. They are on networks
172.17.0.0/16 and 10.2.2.0/24 respectively, and if you want to
talk to any other address on those networks then the routing table
tells it to send directly down that interface. If you want to talk to
anything else not matching those rules, the default rule says to send
it to 172.17.42.1 down the eth0 interface.
So, suppose this container wants to talk to another container at
address 10.2.2.9; it will send down the ethwe interface and weave
Net will take care of routing the traffic. To talk an external server
at address 74.125.133.128, it looks in its routing table, doesn’t
find a match, so uses the default rule.
See Also