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Nmap Network Scanning

Listen Mode Options

See the section called “Access Control Options” for information on limiting the hosts that may connect to the listening Ncat process.

-l, --listen (Listen for connections)

Listen for connections rather than connecting to a remote machine

-m <numconns>, --max-conns <numconns> (Specify maximum number of connections)

The maximum number of simultaneous connections accepted by an Ncat instance. 100 is the default (60 on Windows).

-k, --keep-open (Accept multiple connections)

Normally a listening server accepts only one connection and then quits when the connection is closed. This option makes it accept multiple simultaneous connections and wait for more connections after they have all been closed. It must be combined with --listen. In this mode there is no way for Ncat to know when its network input is finished, so it will keep running until interrupted. This also means that it will never close its output stream, so any program reading from Ncat and looking for end-of-file will also hang.

--broker (Connection brokering)

Allow multiple parties to connect to a centralised Ncat server and communicate with each other. Ncat can broker communication between systems that are behind a NAT or otherwise unable to directly connect. This option is used in conjunction with --listen, which causes the --listen port to have broker mode enabled.

--chat (Ad-hoc chat server)

The --chat option enables chat mode, intended for the exchange of text between several users. In chat mode, connection brokering is turned on. Ncat prefixes each message received with an ID before relaying it to the other connections. The ID is unique for each connected client. This helps distinguish who sent what. Additionally, non-printing characters such as control characters are escaped to keep them from doing damage to a terminal.

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