# TCP Transport

The tcp transport is an implementation of Salt's transport using raw tcp sockets. Since this isn't using a pre-defined messaging library we will describe the wire protocol, message semantics, etc. in this document.

The tcp transport is enabled by changing the `transport` setting to `tcp` on each Salt minion and Salt master.

    transport: tcp

Warning

We currently recommend that when using Syndics that all Masters and Minions use the same transport. We're investigating a report of an error when using mixed transport types at very heavy loads.

## TLS Support

The TLS transport supports full encryption and verification using both server and client certificates. See Transport TLS Support for more details.

## Wire Protocol

This implementation over TCP focuses on flexibility over absolute efficiency. This means we are okay to spend a couple of bytes of wire space for flexibility in the future. That being said, the wire framing is quite efficient and looks like:

    msgpack({'head': SOMEHEADER, 'body': SOMEBODY})

Since msgpack is an iterably parsed serialization, we can simply write the serialized payload to the wire. Within that payload we have two items "head" and "body". Head contains header information (such as "message id"). The Body contains the actual message that we are sending. With this flexible wire protocol we can implement any message semantics that we'd like-- including multiplexed message passing on a single socket.

## Crypto

The current implementation uses the same crypto as the `zeromq` transport.

## Publish Server and Client

For the publish server and client we send messages without "message ids" which the remote end interprets as a one-way send.

Note

As of Salt 2016.3.0, publishes using `list` targeting are sent only to relevant minions and not broadcasted.

As of Salt 3005, publishes using `pcre` and `glob` targeting are also sent only to relevant minions and not broadcasted. Other targeting types are always sent to all minions and rely on minion-side filtering.

Note

Salt CLI defaults to `glob` targeting type, so in order to target specific minions without broadcast, you need to use -L option, such as `salt -L my.minion test.ping`, for masters before 3005.

## Request Server and Client

For the request server and client we send messages with a "message id". This "message id" allows us to multiplex messages across the socket.