Network Controller Microservice

Every ZeroTier virtual network has a network controller responsible for admitting members to the network, issuing certificates, and issuing default configuration information.

This is our reference controller implementation and is the same one we use to power our own hosted services at As of ZeroTier One version 1.2.0 this code is included in normal builds for desktop, laptop, and server (Linux, etc.) targets.

Controller data is stored in JSON format under controller.d in the ZeroTier working directory. It can be copied, rsync'd, placed in git, etc. The files under controller.d should not be modified in place while the controller is running or data loss may result, and if they are edited directly take care not to save corrupt JSON since that can also lead to data loss when the controller is restarted. Going through the API is strongly preferred to directly modifying these files.

See the API section below for information about controlling the controller.

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 the controller uses the filesystem as its data store we recommend fast filesystems and fast SSD drives for heavily loaded controllers.

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. Modern orchestration tools like Nomad and Kubernetes can be of help here.

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.

RethinkDB Database Implementation

The default controller stores its data in the filesystem in controller.d under ZeroTier's home folder. There's an alternative implementation that stores data in RethinkDB that can be built with make central-controller. Right now this is only guaranteed to build and run on Linux and is designed for use with ZeroTier Central. You're welcome to use it but we don't "officially" support it for end-user use and it could change at any time.

Upgrading from Older (1.1.14 or earlier) Versions

Older versions of this code used a SQLite database instead of in-filesystem JSON. A migration utility called migrate-sqlite is included here and must be used to migrate this data to the new format. If the controller is started with an old controller.db in its working directory it will terminate after printing an error to stderr. This is done to prevent "surprises" for those running DIY controllers using the old code.

The migration tool is written in nodeJS and can be used like this:

cd migrate-sqlite
npm install
node migrate.js </path/to/controller.db> </path/to/controller.d>

Network Controller API

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

The controller microservice itself does not implement any fine-grained access control. Access control is via the ZeroTier control interface itself and authtoken.secret. This can be sent as the X-ZT1-Auth HTTP header field or appended to the URL as ?auth=<token>. Take care when doing the latter that request URLs are not being logged.

While networks with any valid ID can be added to the controller's database, it will only actually work to control networks whose first 10 hex digits correspond with the network controller's ZeroTier ID. See section 2.2.1 of the ZeroTier manual.

The controller JSON API is very sensitive about types. Integers must be integers and strings strings, etc. Incorrect types may be ignored, set to default values, or set to undefined values.


  • 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


  • 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.


curl -X POST --header "X-ZT1-Auth: secret" -d '{"name":"my network"}' http://localhost:9993/controller/network/305f406058______

Network object format:

Field Type Description Writable
id string 16-digit network ID no
nwid string 16-digit network ID (legacy) no
objtype string Always "network" no
name string A short name for this network YES
creationTime integer Time network record was created (ms since epoch) no
private boolean Is access control enabled? YES
enableBroadcast boolean Ethernet ff:ff:ff:ff:ff:ff allowed? YES
v4AssignMode object IPv4 management and assign options (see below) YES
v6AssignMode object IPv6 management and assign options (see below) YES
mtu integer Network MTU (default: 2800) 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
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
capabilities array[object] Array of capability objects (see below) YES
tags array[object] Array of tag objects (see below) YES
remoteTraceTarget string 10-digit ZeroTier ID of remote trace target YES
remoteTraceLevel integer Remote trace verbosity level YES
  • 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.
  • Changing the MTU can be disruptive and on some operating systems may require a leave/rejoin of the network or a restart of the ZeroTier service.

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
ACTION_DEBUG_LOG Output debug info on match (if built with rules engine debug) (none)
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

Important notes about rules engine behavior:

  • IPv4 and IPv6 IP address rules do not match for frames that are not IPv4 or IPv6 respectively.
  • ACTION_DEBUG_LOG is a no-op on nodes not built with ZT_RULES_ENGINE_DEBUGGING enabled (see Network.cpp). If that is enabled nodes will dump a trace of rule evaluation results to stdout when this action is encountered but will otherwise keep evaluating rules. This is used for basic "smoke testing" of the rules engine.
  • Multicast packets and packets destined for bridged devices treated a little differently. They are matched more than once. They are matched at the point of send with a NULL ZeroTier destination address, meaning that MATCH_DEST_ZEROTIER_ADDRESS is useless. That's because the true VL1 destination is not yet known. Then they are matched again for each true VL1 destination. On these later subsequent matches TEE actions are ignored and REDIRECT rules are interpreted as DROPs. This prevents multiple TEE or REDIRECT packets from being sent to third party devices.
  • Rules in capabilities are always matched as if the current device is the sender (inbound == false). A capability specifies sender side rules that can be enforced on both sides.

/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
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
revision integer Member revision counter no
vMajor integer Most recently known major version no
vMinor integer Most recently known minor version no
vRev integer Most recently known revision no
vProto integer Most recently known protocl version no

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