Network Controller Microservice
======

ZeroTier's 16-digit network IDs are really just a concatenation of the 10-digit ZeroTier address of a network controller followed by a 6-digit (24-bit) network number on that controller. Fans of software defined networking will recognize this as a spin on the familiar [separation of data plane and control plane](http://sdntutorials.com/difference-between-control-plane-and-data-plane/) SDN design pattern.

This code implements the *node/NetworkController.hpp* interface to provide an embedded microservice configurable via the same local HTTP control plane as ZeroTier One iteself. It is built by default in ZeroTier One in desktop and server builds. This is the same code we use to run [my.zerotier.com](https://my.zerotier.com/), which is a web UI and API that runs in front of a pool of controllers.

Data is stored in JSON format under `controller.d` in the ZeroTier working directory. It can be copied, tar'd, placed in `git`, etc. Technically the JSON files under `controller.d` can also be edited in place, but we do not recommend doing this under a running controller since data loss or corruption might result. Also take care to keep JSON values of the correct types or data loss may also result.

### Scalability and Reliability

Controllers can in theory host up to 2^24 networks and serve many millions of devices (or more), but we recommend spreading large numbers of networks across many controllers for load balancing and fault tolerance reasons.

Since this implementation uses a JSON store in the filesystem we recommend running it on SSD-backed hosts. Slow disks will become a speed bottleneck under heavy load. For really huge and busy controllers you could consider linking `controller.d/` to a folder under `/dev/shm` (Linux RAM disk) and then setting up an out-of-band periodic snapshot cron job or background process to persist the data and a script to populate `/dev/shm` on boot before the controller starts. This is beyond the scope of this guide but is not particularly hard.

Since ZeroTier nodes are mobile and do not need static IPs, implementing high availability fail-over for controllers is easy. Just replicate their working directories from master to backup and have something automatically fire up the backup if the master goes down. Many modern orchestration tools have built-in support for this. It would also be possible in theory to run controllers on a replicated or distributed filesystem, but we haven't tested this yet.

### Dockerizing Controllers

ZeroTier network controllers can easily be run in Docker or other container systems. Since containers do not need to actually join networks, extra privilege options like "--device=/dev/net/tun --privileged" are not needed. You'll just need to map the local JSON API port of the running controller and allow it to access the Internet (over UDP/9993 at a minimum) so things can reach and query it.

### Network Controller API

The controller API is hosted via the same JSON API endpoint that ZeroTier One uses for local control (usually at 127.0.0.1 port 9993). All controller options are routed under the `/controller` base path.

The controller microservice does not implement any fine-grained access control (authentication is via authtoken.secret just like the regular JSON API) or other complex mangement features. It just takes network and network member configurations and reponds to controller queries. We have an enterprise product called [ZeroTier Central](https://my.zerotier.com/) that we host as a service (and that companies can license to self-host) that does this.

All working network IDs on a controller must begin with the controller's ZeroTier address. The API will *allow* "foreign" networks to be added but the controller will have no way of doing anything with them since nobody will know to query it. (In the future we might support secondaries, which would make this relevant.)

The JSON API is *very* sensitive about types. Integers must be integers and strings strings, etc. Incorrectly typed and unrecognized fields may result in ignored fields or a 400 (bad request) error.

#### `/controller`

 * Purpose: Check for controller function and return controller status
 * Methods: GET
 * Returns: { object }

| Field              | Type        | Description                                       | Writable |
| ------------------ | ----------- | ------------------------------------------------- | -------- |
| controller         | boolean     | Always 'true'                                     | no       |
| apiVersion         | integer     | Controller API version, currently 3               | no       |
| clock              | integer     | Current clock on controller, ms since epoch       | no       |

#### `/controller/network`

 * Purpose: List all networks hosted by this controller
 * Methods: GET
 * Returns: [ string, ... ]

This returns an array of 16-digit hexadecimal network IDs.

#### `/controller/network/<network ID>`

 * Purpose: Create, configure, and delete hosted networks
 * Methods: GET, POST, DELETE
 * Returns: { object }

By making queries to this path you can create, configure, and delete networks. DELETE is final, so don't do it unless you really mean it.

When POSTing new networks take care that their IDs are not in use, otherwise you may overwrite an existing one. To create a new network with a random unused ID, POST to `/controller/network/##########______`. The #'s are the controller's 10-digit ZeroTier address and they're followed by six underscores. Check the `nwid` field of the returned JSON object for your network's newly allocated ID. Subsequent POSTs to this network must refer to its actual path.

| Field                 | Type          | Description                                       | Writable |
| --------------------- | ------------- | ------------------------------------------------- | -------- |
| id                    | string        | 16-digit network ID                               | no       |
| nwid                  | string        | 16-digit network ID (old, but still around)       | no       |
| clock                 | integer       | Current clock, ms since epoch                     | no       |
| name                  | string        | A short name for this network                     | YES      |
| private               | boolean       | Is access control enabled?                        | YES      |
| enableBroadcast       | boolean       | Ethernet ff:ff:ff:ff:ff:ff allowed?               | YES      |
| activeBridges         | array[string] | Array of ZeroTier addresses of active bridges     | YES      |
| allowPassiveBridging  | boolean       | Allow any member to bridge (very experimental)    | YES      |
| v4AssignMode          | object        | IPv4 management and assign options (see below)    | YES      |
| v6AssignMode          | object        | IPv6 management and assign options (see below)    | YES      |
| multicastLimit        | integer       | Maximum recipients for a multicast packet         | YES      |
| creationTime          | integer       | Time network was first created                    | no       |
| revision              | integer       | Network config revision counter                   | no       |
| memberRevisionCounter | integer       | Network member revision counter                   | no       |
| authorizedMemberCount | integer       | Number of authorized members (for private nets)   | no       |
| routes                | array[object] | Managed IPv4 and IPv6 routes; see below           | YES      |
| ipAssignmentPools     | array[object] | IP auto-assign ranges; see below                  | YES      |
| rules                 | array[object] | Traffic rules; see below                          | YES      |

Recent changes:

 * The `ipLocalRoutes` field appeared in older versions but is no longer present. Routes will now show up in `routes`.
 * The `relays` field is gone since network preferred relays are gone. This capability is replaced by VL1 level federation ("federated roots").
 * Active bridges are now set at the network level, not in individual member configs.

Other important points:

 * Networks without rules won't carry any traffic. If you don't specify any on network creation an "accept anything" rule set will automatically be added.
 * Managed IP address assignments and IP assignment pools that do not fall within a route configured in `routes` are ignored and won't be used or sent to members.
 * The default for `private` is `true` and this is probably what you want. Turning `private` off means *anyone* can join your network with only its 16-digit network ID. It's also impossible to de-authorize a member as these networks don't issue or enforce certificates. Such "party line" networks are used for decentralized app backplanes, gaming, and testing but are otherwise not common.

**Auto-Assign Modes:**

Auto assign modes (`v4AssignMode` and `v6AssignMode`) contain objects that map assignment modes to booleans.

For IPv4 the only valid setting is `zt` which, if true, causes IPv4 addresses to be auto-assigned from `ipAssignmentPools` to members that do not have an IPv4 assignment. Note that active bridges are exempt and will not get auto-assigned IPs since this can interfere with bridging. (You can still manually assign one if you want.)

IPv6 includes this option and two others: `6plane` and `rfc4193`. These assign private IPv6 addresses to each member based on a deterministic assignment scheme that allows members to emulate IPv6 NDP to skip multicast for better performance and scalability. The `rfc4193` mode gives every member a /128 on a /88 network, while `6plane` gives every member a /80 within a /40 network but uses NDP emulation to route *all* IPs under that /80 to its owner. The `6plane` mode is great for use cases like Docker since it allows every member to assign IPv6 addresses within its /80 that just work instantly and globally across the network.

**IP assignment pool object format:**

| Field                 | Type          | Description                                       |
| --------------------- | ------------- | ------------------------------------------------- |
| ipRangeStart          | string        | Starting IP address in range                      |
| ipRangeEnd            | string        | Ending IP address in range (inclusive)            |

Pools are only used if auto-assignment is on for the given address type (IPv4 or IPv6) and if the entire range falls within a managed route.

IPv6 ranges work just like IPv4 ranges and look like this:

    {
        "ipRangeStart": "fd00:feed:feed:beef:0000:0000:0000:0000",
        "ipRangeEnd": "fd00:feed:feed:beef:ffff:ffff:ffff:ffff"
    }

(You can POST a shortened-form IPv6 address but the API will always report back un-shortened canonical form addresses.)

That defines a range within network `fd00:feed:feed:beef::/64` that contains up to 2^64 addresses. If an IPv6 range is large enough, the controller will assign addresses by placing each member's device ID into the address in a manner similar to the RFC4193 and 6PLANE modes. Otherwise it will assign addresses at random.

**Rule object format:**

Each rule is actually a sequence of zero or more `MATCH_` entries in the rule array followed by an `ACTION_` entry that describes what to do if all the preceding entries match. An `ACTION_` without any preceding `MATCH_` entries is always taken, so setting a single `ACTION_ACCEPT` rule yields a network that allows all traffic. If no rules are present the default action is `ACTION_DROP`.

Rules are evaluated in the order in which they appear in the array. There is currently a limit of 256 entries per network. Capabilities should be used if a larger and more complex rule set is needed since they allow rules to be grouped by purpose and only shipped to members that need them.

Each rule table entry has two common fields.

| Field                 | Type          | Description                                       |
| --------------------- | ------------- | ------------------------------------------------- |
| type                  | string        | Entry type (all caps, case sensitive)             |
| not                   | boolean       | If true, MATCHes match if they don't match        |

The following fields may or may not be present depending on rule type:

| Field                 | Type          | Description                                       |
| --------------------- | ------------- | ------------------------------------------------- |
| zt                    | string        | 10-digit hex ZeroTier address                     |
| etherType             | integer       | Ethernet frame type                               |
| mac                   | string        | Hex MAC address (with or without :'s)             |
| ip                    | string        | IPv4 or IPv6 address                              |
| ipTos                 | integer       | IP type of service                                |
| ipProtocol            | integer       | IP protocol (e.g. TCP)                            |
| start                 | integer       | Start of an integer range (e.g. port range)       |
| end                   | integer       | End of an integer range (inclusive)               |
| id                    | integer       | Tag ID                                            |
| value                 | integer       | Tag value or comparison value                     |
| mask                  | integer       | Bit mask (for characteristics flags)              |

The entry types and their additional fields are:

| Entry type                      | Description                                                       | Fields         |
| ------------------------------- | ----------------------------------------------------------------- | -------------- |
| `ACTION_DROP`                   | Drop any packets matching this rule                               | (none)         |
| `ACTION_ACCEPT`                 | Accept any packets matching this rule                             | (none)         |
| `ACTION_TEE`                    | Send a copy of this packet to a node (rule parsing continues)     | `zt`           |
| `ACTION_REDIRECT`               | Redirect this packet to another node                              | `zt`           |
| `MATCH_SOURCE_ZEROTIER_ADDRESS` | Match VL1 ZeroTier address of packet sender.                      | `zt`           |
| `MATCH_DEST_ZEROTIER_ADDRESS`   | Match VL1 ZeroTier address of recipient                           | `zt`           |
| `MATCH_ETHERTYPE`               | Match Ethernet frame type                                         | `etherType`    |
| `MATCH_MAC_SOURCE`              | Match source Ethernet MAC address                                 | `mac`          |
| `MATCH_MAC_DEST`                | Match destination Ethernet MAC address                            | `mac`          |
| `MATCH_IPV4_SOURCE`             | Match source IPv4 address                                         | `ip`           |
| `MATCH_IPV4_DEST`               | Match destination IPv4 address                                    | `ip`           |
| `MATCH_IPV6_SOURCE`             | Match source IPv6 address                                         | `ip`           |
| `MATCH_IPV6_DEST`               | Match destination IPv6 address                                    | `ip`           |
| `MATCH_IP_TOS`                  | Match IP TOS field                                                | `ipTos`        |
| `MATCH_IP_PROTOCOL`             | Match IP protocol field                                           | `ipProtocol`   |
| `MATCH_IP_SOURCE_PORT_RANGE`    | Match a source IP port range                                      | `start`,`end`  |
| `MATCH_IP_DEST_PORT_RANGE`      | Match a destination IP port range                                 | `start`,`end`  |
| `MATCH_CHARACTERISTICS`         | Match on characteristics flags                                    | `mask`,`value` |
| `MATCH_FRAME_SIZE_RANGE`        | Match a range of Ethernet frame sizes                             | `start`,`end`  |
| `MATCH_TAGS_SAMENESS`           | Match if both sides' tags differ by no more than value            | `id`,`value`   |
| `MATCH_TAGS_BITWISE_AND`        | Match if both sides' tags AND to value                            | `id`,`value`   |
| `MATCH_TAGS_BITWISE_OR`         | Match if both sides' tags OR to value                             | `id`,`value`   |
| `MATCH_TAGS_BITWISE_XOR`        | Match if both sides` tags XOR to value                            | `id`,`value`   |

Notes:

 * `MATCH_DEST_ZEROTIER_ADDRESS` does not work for multicast packets since these have many and varying destinations and can take circuitous routes. Use MAC rules instead.
 * IPv4 and IPv6 rules do not match for frames that are not IPv4 or IPv6 respectively.

#### `/controller/network/<network ID>/member`

 * Purpose: Get a set of all members on this network
 * Methods: GET
 * Returns: { object }

This returns a JSON object containing all member IDs as keys and their `memberRevisionCounter` values as values.

#### `/controller/network/<network ID>/active`

 * Purpose: Get a set of all active members on this network
 * Methods: GET
 * Returns: { object }

This returns an object containing all currently online members and the most recent `recentLog` entries for their last request.

#### `/controller/network/<network ID>/member/<address>`

 * Purpose: Create, authorize, or remove a network member
 * Methods: GET, POST, DELETE
 * Returns: { object }

| Field                 | Type          | Description                                       | Writable |
| --------------------- | ------------- | ------------------------------------------------- | -------- |
| id                    | string        | Member's 10-digit ZeroTier address                | no       |
| address               | string        | Member's 10-digit ZeroTier address                | no       |
| nwid                  | string        | 16-digit network ID                               | no       |
| clock                 | integer       | Current clock, ms since epoch                     | no       |
| authorized            | boolean       | Is member authorized? (for private networks)      | YES      |
| activeBridge          | boolean       | Member is able to bridge to other Ethernet nets   | YES      |
| identity              | string        | Member's public ZeroTier identity (if known)      | no       |
| ipAssignments         | array[string] | Managed IP address assignments                    | YES      |
| memberRevision        | integer       | Member revision counter                           | no       |
| recentLog             | array[object] | Recent member activity log; see below             | no       |

Note that managed IP assignments are only used if they fall within a managed route. Otherwise they are ignored.

**Recent log object format:**

| Field                 | Type          | Description                                       |
| --------------------- | ------------- | ------------------------------------------------- |
| ts                    | integer       | Time of request, ms since epoch                   |
| authorized            | boolean       | Was member authorized?                            |
| clientMajorVersion    | integer       | Client major version or -1 if unknown             |
| clientMinorVersion    | integer       | Client minor version or -1 if unknown             |
| clientRevision        | integer       | Client revision or -1 if unknown                  |
| fromAddr              | string        | Physical address if known                         |

The controller can only know a member's `fromAddr` if it's able to establish a direct path to it. Members behind very restrictive firewalls may not have this information since the controller will be receiving the member's requests by way of a relay. ZeroTier does not back-trace IP paths as packets are relayed since this would add a lot of protocol overhead.