Raj Chaudhuri
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68 lines
3.0 KiB
Markdown
68 lines
3.0 KiB
Markdown
---
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title: IP Addresses, Routes and Networks
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menu_order: 40
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search_type: Documentation
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---
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Weave Net runs containers on a private network, which means that IP addresses are isolated from the rest of the
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Internet, and that you don't have to worry about addresses clashing.
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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]({{ '/tasks/ipam/manual-ip-address' | relative_url }})
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### Some Definitions
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- _IP_ is the Internet Protocol, the fundamental basis of network
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communication between billions of connected devices.
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- The _IP address_ is (for most purposes) the four numbers separated
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by dots, like `192.168.48.12`. Each number is one byte in size, so can
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be between 0 and 255.
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- Each IP address lives on a _Network_, which is some set of those
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addresses that all know how talk to each other. The network address
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is some prefix of the IP address, like `192.168.48`. To show
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which part of the address is the network, we append a slash
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and then the number of bits in the network prefix, like
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`/24`.
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- A _route_ is an instruction for how to deal with traffic destined
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for somewhere else - it specifies a Network, and a way to talk to
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that network. Every device using IP has a table of routes, so for
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any destination address it looks up that table, finds the right
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route, and sends it in the direction indicated.
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### IP Address Notation in Weave
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In the IP address `10.4.2.6/8`, the network prefix is the first 8 bits
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\- `10`. Written out in full, that network is `10.0.0.0/8`.
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The most common prefix lengths are 8, 16 and 24, but there is nothing
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stopping you using a /9 network or a /26. For example, `6.250.3.1/9` is on the
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`6.128.0.0/9` network.
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Several websites offer calculators to decode this kind of address, see, for example: [IP Address Guide](http://www.ipaddressguide.com/cidr).
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The following is an example route table for a container that is attached to a Weave
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network:
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# ip route show
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default via 172.17.42.1 dev eth0
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10.2.2.0/24 dev ethwe proto kernel scope link src 10.2.2.1
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172.17.0.0/16 dev eth0 proto kernel scope link src 172.17.0.170
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It has two interfaces: one that Docker gave it called `eth0`, and one
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that weave gave it called `ethwe`. They are on networks
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`172.17.0.0/16` and `10.2.2.0/24` respectively, and if you want to
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talk to any other address on those networks then the routing table
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tells it to send directly down that interface. If you want to talk to
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anything else not matching those rules, the default rule says to send
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it to `172.17.42.1` down the eth0 interface.
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So, suppose this container wants to talk to another container at
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address `10.2.2.9`; it will send down the ethwe interface and weave
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Net will take care of routing the traffic. To talk an external server
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at address `74.125.133.128`, it looks in its routing table, doesn't
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find a match, so uses the default rule.
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**See Also**
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* [Allocating IPs in a Specific Range]({{ '/tasks/ipam/configuring-weave' | relative_url }})
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