SSH

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.

Configuration

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. You can choose from the following 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. Supported MACs: hmac-md5, hmac-md5-96, hmac-ripemd160, hmac-sha1, hmac-sha1-96, hmac-sha2-256, hmac-sha2-512, umac-64@openssh.com, umac-128@openssh.com, hmac-md5-etm@openssh.com, hmac-md5-96-etm@openssh.com, hmac-ripemd160-etm@openssh.com, hmac-sha1-etm@openssh.com, hmac-sha1-96-etm@openssh.com, hmac-sha2-256-etm@openssh.com, hmac-sha2-512-etm@openssh.com, umac-64-etm@openssh.com, umac-128-etm@openssh.com

Note

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

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. 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 curve25519-sha256@libssh.org.

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.