# COM\_REGISTER\_SLAVE

This command is sent by the replica server to start MariaDB replication, and should be sent before requesting binlog events with [COM\_BINLOG\_DUMP](/docs/server/reference/clientserver-protocol/replication-protocol/com_binlog_dump.md).

The payload is:

* [uint<1>](/docs/server/reference/clientserver-protocol/protocol-data-types.md#fixed-length-bytes) command (`COM_REGISTER_SLAVE` = `0x15`).
* [uint<4>](/docs/server/reference/clientserver-protocol/protocol-data-types.md#fixed-length-bytes) Replica server ID.
* [uint<1>](/docs/server/reference/clientserver-protocol/protocol-data-types.md#fixed-length-bytes) Replica hostname length.
* [string\<n>](/docs/server/reference/clientserver-protocol/protocol-data-types.md#fixed-length-bytes) Hostname.
* [uint<1>](/docs/server/reference/clientserver-protocol/protocol-data-types.md#fixed-length-bytes) Replica username length.
* [string\<n>](/docs/server/reference/clientserver-protocol/protocol-data-types.md#fixed-length-bytes) Username.
* [uint<1>](/docs/server/reference/clientserver-protocol/protocol-data-types.md#fixed-length-bytes) Replica password length.
* [string\<n>](/docs/server/reference/clientserver-protocol/protocol-data-types.md#fixed-length-bytes) Replica password.
* [uint<2>](/docs/server/reference/clientserver-protocol/protocol-data-types.md#fixed-length-bytes) Replica connection port.
* [uint<4>](/docs/server/reference/clientserver-protocol/protocol-data-types.md#fixed-length-bytes) Replication rank.
* [uint<4>](/docs/server/reference/clientserver-protocol/protocol-data-types.md#fixed-length-bytes) Master server ID.

**Note**:

* Replica hostname, replica user, replica password, and replica port are usually not set. Some replica [replication parameters](/docs/server/ha-and-performance/standard-replication/replication-and-binary-log-system-variables.md) can be used for such settings (`report_host`, `report_port`, and so forth).
* Replication rank is not set.
* Master server ID is not set either.

## Example of COM\_REGISTER\_SLA

The replica server is configured with:

* server-id=10101;
* report-host=slave\_n\_1;
* report-port=23241.

```
1b 00 00 00 15 75 27 00    00 09 73 6c 61 76 65 5f    .....u'...slave_
 6e 5f 31 00 00 c9 5a 00    00 00 00 00 00 00 00       n_1...Z.......
```

We can see from the example:

* server\_id \[4] = 75 27 00 00 => 10101.
* hostname\_len \[1] = 09.
* hostname\[n] = slave\_n\_1 (9 bytes).
* username len \[1] = 0 (not set).
* password len \[1] = 0 (not set).
* slave port \[2] = c9 5a => 23241.
* rank \[4] = 0.
* master server id = 0.

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