# 8 Implementation details of net.tcp.service checks

#### Overview

Implementation of net.tcp.service checks is detailed in this section for
various services specified in the service parameter.

**ftp**

Creates a TCP connection and expects the first 3 characters of the
response to be "220" response, then sends "QUIT\\n". Default port 21 is
used if not specified.

**http**

Creates a TCP connection without expecting and sending anything. Default
port 80 is used if not specified.

**https**

Uses (and only works with) libcurl, does not verify the authenticity of
the certificate, does not verify the host name in the SSL certificate,
only fetches the response header (HEAD request). Default port 443 is
used if not specified.

**imap**

Creates a TCP connection and expects the first 4 characters of the
response to be "\* OK", then sends "a1 LOGOUT\\n". Default port 143 is
used if not specified.

**ldap**

Opens a connection to an LDAP server and performs an LDAP search
operation with filter set to (objectClass=\*). Expects successful
retrieval of the first attribute of the first entry. Default port 389 is
used if not specified.

**nntp**

Creates a TCP connection and expects the first 3 characters of the
response to be "200", then sends "QUIT\\n". Default port 119 is used if
not specified.

**ntp**

Sends an SNTP packet over UDP and validates the response according to
[RFC 4330, section 5](http://tools.ietf.org/html/rfc4330#section-5).
Default port 123 is used if not specified.

**pop**

Creates a TCP connection and expects the first 3 characters of the
response to be "+OK", then sends "QUIT\\n". Default port 110 is used if
not specified.

**smtp**

Creates a TCP connection and expects the first 3 characters of the
response to be "220". Then sends "QUIT\\r\\n". Default port 25 is used
if not specified.

**ssh**

Creates a TCP connection. If the connection has been established, both
sides exchange an identification string (SSH-major.minor-XXXX), where
major and minor are protocol versions and XXXX is a string. Zabbix
checks if the string matching the specification is found and then sends
back the string "SSH-major.minor-zabbix\_agent\\r\\n" or "0\\n" on
mismatch. Default port 22 is used if not specified.

**tcp**

Creates a TCP connection without expecting and sending anything. Unlike
the other checks requires the port parameter to be specified.

**telnet**

Creates a TCP connection and expects a login prompt (':' at the end).
Default port 23 is used if not specified.