connect: Performs a TCP connect to a server. Useful for testing non-supported protocols.
dns: Checks DNS servers for correct resolving of host names.
domain: Checks DNS servers for consistent and correct behaviour for a specific domain.
domain: Checks DNS servers for consistent and correct behaviour for a specific domain.
ftp: Checks the FTP protocol, used in file transfers.
ftps: Checks the FTP protocol, used in file transfers from SSL-secured FTP servers
http: Checks the HTTP protocol, which is used for non-secured web sites.
https: Checks the HTTPS protocol, used on SSL-secured web sites.
imap: Checks the IMAP protocol, which is used for email retrieval
ldap: Checks the LDAP protocol, which is used to access remote directory services.
ping: Sends PINGs (ICMP 'echo request' packets) and checks packet loss.
plugin: Used for monitoring servers behind a firewall.
pop3: Checks the POP3 protocol, which is used for email retrieval
scp: Checks the SCP protocol, used in file transfers over SSH
sftp: Checks the FTP protocol, used in file transfers over SSH
sip: Checks the SIP protocol, which is used for VoIP, Instant Messaging, presence applications, etc.
smtp: Checks the SMTP protocol, which is used for (outgoing) email transmission
