SSH is a cryptographic network protocol for operating network services securely over an unsecured network. The standard TCP port for SSH is 22. The best known example application is for remote login to computer systems by users.

SSH provides a secure channel over an unsecured network in a client-server architecture, connecting an SSH client application with an SSH server. Common applications include remote command-line login and remote command execution, but any network service can be secured with SSH. The protocol specification distinguishes between two major versions, referred to as SSH-1 and SSH-2.

The most visible application of the protocol is for access to shell accounts on Unix-like operating systems, but it sees some limited use on Windows as well. In 2015, Microsoft announced that they would include native support for SSH in a future release.

SSH was designed as a replacement for Telnet and for unsecured remote shell protocols such as the Berkeley rlogin, rsh, and rexec protocols. Those protocols send information, notably passwords, in plaintext, rendering them susceptible to interception and disclosure using packet analysis. The encryption used by SSH is intended to provide confidentiality and integrity of data over an unsecured network, such as the Internet.


VyOS 1.1 supported login as user root. This has been removed due to tighter security in VyOS 1.2.


set service ssh port <port>

Enabling SSH only requires you to specify the port <port> you want SSH to listen on. By default, SSH runs on port 22.

set service ssh listen-address <address>

Specify IPv4/IPv6 listen address of SSH server. Multiple addresses can be defined.

set service ssh ciphers <cipher>

Define allowed ciphers used for the SSH connection. A number of allowed ciphers can be specified, use multiple occurrences to allow multiple ciphers.

List of supported ciphers: 3des-cbc, aes128-cbc, aes192-cbc, aes256-cbc, aes128-ctr, aes192-ctr, aes256-ctr, arcfour128, arcfour256, arcfour, blowfish-cbc, cast128-cbc

set service ssh disable-password-authentication

Disable password based authentication. Login via SSH keys only. This hardens security!

set service ssh disable-host-validation

Disable the host validation through reverse DNS lookups - can speedup login time when reverse lookup is not possible.

set service ssh macs <mac>

Specifies the available MAC algorithms. The MAC algorithm is used in protocol version 2 for data integrity protection. Multiple algorithms can be provided.

List of supported MACs: hmac-md5, hmac-md5-96, hmac-ripemd160, hmac-sha1, hmac-sha1-96, hmac-sha2-256, hmac-sha2-512,,,,,,,,,,,

set service ssh access-control <allow | deny> <group | user> <name>

Add access-control directive to allow or deny users and groups. Directives are processed in the following order of precedence: deny-users, allow-users, deny-groups and allow-groups.

set service ssh client-keepalive-interval <interval>

Specify timeout interval for keepalive message in seconds.

set service ssh key-exchange <kex>

Specify allowed KEX algorithms.

List of supported algorithms: diffie-hellman-group1-sha1, diffie-hellman-group14-sha1, diffie-hellman-group14-sha256, diffie-hellman-group16-sha512, diffie-hellman-group18-sha512, diffie-hellman-group-exchange-sha1, diffie-hellman-group-exchange-sha256, ecdh-sha2-nistp256, ecdh-sha2-nistp384, ecdh-sha2-nistp521, curve25519-sha256 and

set service ssh loglevel <quiet | fatal | error | info | verbose>

Set the sshd log level. The default is info.

set service ssh vrf <name>

Specify name of the VRF instance.


Protects host from brute-force attacks against SSH. Log messages are parsed, line-by-line, for recognized patterns. If an attack, such as several login failures within a few seconds, is detected, the offending IP is blocked. Offenders are unblocked after a set interval.

set service ssh dynamic-protection

Allow ssh dynamic-protection.

set service ssh dynamic-protection allow-from <address | prefix>

Whitelist of addresses and networks. Always allow inbound connections from these systems.

set service ssh dynamic-protection block-time <sec>

Block source IP in seconds. Subsequent blocks increase by a factor of 1.5 The default is 120.

set service ssh dynamic-protection detect-time <sec>

Remember source IP in seconds before reset their score. The default is 1800.

set service ssh dynamic-protection threshold <sec>

Block source IP when their cumulative attack score exceeds threshold. The default is 30.


restart ssh

Restart the SSH daemon process, the current session is not affected, only the background daemon is restarted.

generate ssh server-key

Re-generated the public/private keyportion which SSH uses to secure connections.


Already learned known_hosts files of clients need an update as the public key will change.

generate ssh client-key /path/to/private_key

Re-generated a known pub/private keyfile which can be used to connect to other services (e.g. RPKI cache).


vyos@vyos:~$ generate ssh client-key /config/auth/id_rsa_rpki
Generating public/private rsa key pair.
Your identification has been saved in /config/auth/id_rsa_rpki.
Your public key has been saved in /config/auth/
The key fingerprint is:
SHA256:XGv2PpdOzVCzpmEzJZga8hTRq7B/ZYL3fXaioLFLS5Q vyos@vyos
The key's randomart image is:
+---[RSA 2048]----+
|         oo      |
|          ..o    |
|       . o.o.. o.|
|       o+ooo  o.o|
|        Eo*  =.o |
|       o = +.o*+ |
|        = o *.o.o|
|       o * +.o+.+|
|        =.. o=.oo|

Two new files /config/auth/id_rsa_rpki and /config/auth/ will be created.

generate public-key-command user <username> path <location>

Generate the configuration mode commands to add a public key for Key Based Authentication. <location> can be a local path or a URL pointing at a remote file.

Supported remote protocols are FTP, FTPS, HTTP, HTTPS, SCP/SFTP and TFTP.


alyssa@vyos:~$ generate public-key-command user alyssa path s
# To add this key as an embedded key, run the following commands:
set system login user alyssa authentication public-keys [email protected] key AAA...
set system login user alyssa authentication public-keys [email protected] type ssh-rsa

ben@vyos:~$ generate public-key-command user ben path ~/.ssh/
# To add this key as an embedded key, run the following commands:
set system login user ben authentication public-keys ben@vyos key AAA...
set system login user ben authentication public-keys ben@vyos type ssh-dss
show log ssh

Show SSH server log.

monitor log ssh

Follow the SSH server log.

show log ssh dynamic-protection

Show SSH dynamic-protection log.

monitor log ssh dynamic-protection

Follow the SSH dynamic-protection log.

show ssh dynamic-protection

Show list of IPs currently blocked by SSH dynamic-protection.

show ssh fingerprints

Show SSH server public key fingerprints.

show ssh fingerprints ascii

Show SSH server public key fingerprints, including a visual ASCII art representation.