Ubiquiti’s or UI’s GPONs do not have a SSH client by default. Or do they?
If you type “ssh” and hit return, you’ll receive a “not found” error.
Typically on devices like home routers, GPONs, UniFi AP’s etc, ssh is handled by Dropbear. Dropbear provides a Secure Shell compatible server and client and is typically used in embedded systems.
To SSH from a GPON to another device, use dbclient
dbclient ubnt@192.168.1.20
dbclient is the Dropbear client. AKA, SSH client.
From the server side, edit the /etc/ssh/sshd_config
Change, uncomment, or add
ClientAliveInterval 120
ClientAliveCountMax 15
Change the AliveInterval and CountMax as desired.
More info on the AliveIntercal and CountMax.
ClientAliveCountMax Sets the number of client alive messages which may be sent without sshd(8) receiving any messages back from the client. If this threshold is reached while client alive messages are being sent, sshd will disconnect the client, terminating the session. It is important to note that the use of client alive messages is very different from TCPKeepAlive. The client alive messages are sent through the encrypted channel and therefore will not be spoofable. The TCP keepalive option enabled by TCPKeepAlive is spoofable. The client alive mechanism is valuable when the client or server depend on knowing when a connection has become unresponsive.
The default value is 3. If ClientAliveInterval is set to 15, and ClientAliveCountMax is left at the default, unresponsive SSH clients will be disconnected after approximately 45 seconds. Setting a zero
ClientAliveCountMax disables connection termination.ClientAliveInterval Sets a timeout interval in seconds after which if no data has been received from the client, sshd(8) will send a message through the encrypted channel to request a response from the client. The default is 0, indicating that these messages will not be sent to the client.
More information
https://man.openbsd.org/sshd_config
Debian / Ubuntu
sudo apt-get install -y openssh-server
RPM based Distros, Fedora / CentOS / RedHat
sudo dnf install -y openssh-server
or use yum
sudo yum install -y openssh-server
Start ssh service
sudo systemctl start sshd
By default the SSH service should start when the system starts, but if not try the following command to enable the service on boot up.
Debian / Ubuntu
systemctl enable ssh
Fedora, CentOS, RedHat
systemctl enable sshd
Change SSH port
Not necessary, but it is a good idea to change the default ssh port. To change the port edit the sshd file.
vi /etc/ssh/sshd_config
If you change the port, you’ll need to allow it in the firewall (firewalld, iptables) and if SELinux is enabled, semanage.