You can log in to one device and access another device using Telnet, FTP, TFTP or SFTP.
As shown in Figure 1, after you use the terminal emulator or Telnet program on a PC to connect to the router, you can use Telnet, FTP, TFTP or SFTP to access other devices from the router functioning as a client.
Telnet is an application layer protocol in the TCP/IP protocol suite and provides remote login and virtual terminal services. The NetEngine 8000 F provides the following Telnet services:
Telnet client: After using the terminal emulator or Telnet client program on a PC to connect to the device, a user runs the telnet command to log in to another device for configuration and management. The device functions as a Telnet client. In Figure 2, the CE functions as both a Telnet server and a Telnet client.
When the network works properly, entering the shortcut key Ctrl_] causes the Telnet server to interrupt the current Telnet connection.
For example, after you enter Ctrl_] on P3, the <P2> prompt is displayed.
<P3> Select Ctrl_] to return to the prompt of P2 The connection was closed by the remote host. <P2>
After you enter Ctrl_] on P2, the <P1> prompt is displayed.
<P2> Ctrl_] The connection was closed by the remote host. <P1>
If the network connection is disconnected, shortcut keys do not take effect.
When the server fails and the client is unaware of the failure, the server does not respond to the client's input. If you enter Ctrl_K, the Telnet client interrupts and quits the Telnet connection.
For example, enter Ctrl_K on P3 to quit the Telnet connection.
<P3> Ctrl_K <P1>
When the number of remote login users reaches the maximum number of VTY user interfaces, the system prompts subsequent users with a message, indicating that all user interfaces are in use and no more Telnet connections are allowed.
Before users log in, the network administrator must configure an IP address for the FTP server.
TFTP is an application protocol based on User Datagram Protocol (UDP) connections. It uses the UDP port number 69 to transfer files between local hosts and remote servers. Unlike FTP, TFTP is simple, providing no authentication. It is applicable to scenarios where complicated interactions between clients and the server are not required.
TFTP supports both binary and ASCII file transfer modes, which are also supported by FTP.
SFTP uses SSH to ensure secure file transfer. On one hand, SFTP allows remote users to securely log in to the device to manage and transfer files. On the other hand, users can use the device functioning as a client to log in to a remote server and transfer files securely.