SSH Commands to a Cisco Switch

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Demonstrates establishing an SSH session with a Cisco switch (or similar device) and sending commands in a device console session. Each command is sent, and its output is read up to the device's next prompt.

Note: QuickShell allocates a PTY, which is what a network device console expects. The device presents an interactive prompt, and each command's output is read up to the next prompt.

Background: Network devices differ from general-purpose servers in that they expose a menu- or prompt-driven console rather than a Unix shell, so exec requests are usually unavailable and driving the interactive console is the only option. That makes prompt matching the synchronization mechanism, and it is why a PTY is appropriate here despite the general advice to avoid one. Retrieving the received text between commands is essential: a prompt left in the buffer would make the next receive return immediately with the wrong output.

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bool success = false;

//  This example requires the Chilkat API to have been previously unlocked.
//  See Global Unlock Sample for sample code.

//  Demonstrates establishing an SSH session with a Cisco switch (or similar device) and sending
//  commands in a device console session.
//  
//  Note: QuickShell allocates a PTY, which is what a network device console expects.  The device
//  presents an interactive prompt, and each command's output is read up to the next prompt.

Chilkat.Ssh ssh = new Chilkat.Ssh();

int port = 22;
success = ssh.Connect("172.16.16.100",port);
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

//  Normally you would not hard-code the password in source.  You should instead obtain it
//  from an interactive prompt, environment variable, or a secrets vault.
string password = "mySshPassword";

success = ssh.AuthenticatePw("mySshLogin",password);
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

//  Start a shell session.
int channelNum = ssh.QuickShell();
if (channelNum < 0) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

//  IMPORTANT: Set a read timeout before receiving until a match.  ReadTimeoutMs defaults to 0,
//  which means no limit -- without it, this call waits forever if the received data never
//  contains a match.
ssh.ReadTimeoutMs = 15000;

bool caseSensitive = true;

//  The switch presents a prompt ending in "#".  Reading up to it confirms the session is ready.
success = ssh.ChannelReceiveUntilMatch(channelNum,"#","utf-8",caseSensitive);
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

string cmdOutput = ssh.GetReceivedText(channelNum,"utf-8");
if (ssh.LastMethodSuccess == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

Debug.WriteLine(cmdOutput);

//  Send a command and read its output up to the next prompt.
success = ssh.ChannelSendString(channelNum,"show clock\n","utf-8");
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

success = ssh.ChannelReceiveUntilMatch(channelNum,"#","utf-8",caseSensitive);
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

//  Retrieving the text also clears the receive buffer, which matters: if the prompt were left
//  buffered, the next receive would match it immediately and return the wrong output.
cmdOutput = ssh.GetReceivedText(channelNum,"utf-8");
if (ssh.LastMethodSuccess == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

Debug.WriteLine(cmdOutput);

//  Additional commands follow the same send / read-to-prompt / retrieve pattern.
success = ssh.ChannelSendString(channelNum,"show version\n","utf-8");
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

success = ssh.ChannelReceiveUntilMatch(channelNum,"#","utf-8",caseSensitive);
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

cmdOutput = ssh.GetReceivedText(channelNum,"utf-8");
if (ssh.LastMethodSuccess == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

Debug.WriteLine(cmdOutput);

ssh.Disconnect();