FAQ: Connection failure - 0 bytes received
In SecureCRT, SecureFX, or SFXCL, if an SSH/SFTP connection attempt fails, it may be that the network connections from your app/computer are being blocked from successfully making outgoing connections. This could be caused by a misconfigured firewall (either hardware or software), a switch, router or some other device between you and the server that is not allowing the connection to go through to the remote server or not relaying back its response. It might also be caused by an application installed on your system that restricts/controls an application's ability to even make outgoing network connections -- in which case an exception may need to be added in order for SecureCRT, SecureFX, or SFXCL to successfully make an outgoing network connection.
This article addresses two common scenarios you might see in a SecureFX/SFXCL log, or in SecureCRT with Trace Options debug output enabled (File > Trace Options).
Connected for s seconds, 0 bytes sent, 0 bytes received
In this situation, SecureCRT/SecureFX/SFXCL has asked the operating system to make a TCP connection to the specified host/address. The connection was not established, so no data (bytes) could be sent and no data could be received. This is usually caused by one of these scenarios, all of which are outside SecureCRT's/SecureFX's/SFXCL's ability to fix/resolve:
Connected for s seconds, n bytes sent, 0 bytes received
In this situation, SecureCRT/SecureFX/SFXCL was able to get successfully connected to at least send some initial data over the established connection. Typically, the number of bytes sent is equal to the SSH2 ident string that the product sends as the initial protocol handshake to begin setting up the SSH connection with the remote SSH2/SFTP server. For example, a 64-bit SecureCRT 8.5.1 sends the following ident string for negotiating the SSH2 protocol with a server:
SSH-2.0-SecureCRT_8.5.1 (x64 build 1764) 123456789 123456789 123456789 123456789 123456789 123456789
This scenario where a non-zero amount of bytes are sent, but 0 bytes are received is caused when the remote server -- or any networking firewall/proxy in between the client and the server -- accepts the connection, but when SecureCRT/SecureFX/SFXCL sent its ident string the connection was then immediately closed, or timed out later without SecureCRT/SecureFX/SFXCL receiving any bytes back from the connected peer.
Possible causes include:
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Last edited by jdev; 04-23-2019 at 12:03 PM. Reason: Change icon to question mark
|0 bytes , connection failure , securecrt , securefx , sfxcl , timeout|