Advanced Connection Options

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Public Key Authentication

Public key authentication is not supported on FarmShare systems.

GSSAPI Authentication

FarmShare systems do support password-less authentication using GSSAPI if you have a valid Kerberos ticket for the stanford.edu realm.

OpenSSH

On macOS and Linux systems you can enable GSSAPI by adding the following lines to ~/.ssh/config on your local system.

GSSAPIKeyExchange yes
GSSAPIAuthentication yes

Recent versions of macOS no longer support the GSSAPIKeyExchange option; you can either omit this option or, if you prefer to keep a standard configuration, add the additional option IgnoreUnknown GSSAPIKeyExchange to your ~/.ssh/config file.

In some cases GSSAPI authentication may be enabled by default, but ssh will not forward your Kerberos ticket to the remote system. This can be inconvenient, especially in the legacy FarmShare environment, or when you expect to access AFS on rice. You can enable forwarding by adding GSSAPIDelegateCredentials yes to ~/.ssh/config, but you should do so only for trusted systems; to restrict the option, add it to a Host block:

Host rice rice.stanford.edu rice?? rice??.stanford.edu cardinal cardinal.stanford.edu cardinal? cardinal?.stanford.edu
  GSSAPIDelegateCredentials yes

See the man page for ssh_config for more information on GSSAPI options.

PuTTY

PuTTY supports GSSAPI authentication by default; to enable forwarding, select Connection → SSH → AuthGSSAPIAllow GSSAPI credential delegation.

SecureCRT

SecureCRT supports GSSAPI authentication, but it is disabled by default. To enable GSSAPI, open the Session Options dialog and select ConnectionSSH2AuthenticationGSSAPI and ConnectionSSH2AuthenticationKey exchangeKerberos (Group Exchange). SecureCRT attempts authentication and key exchange methods in the order listed, so these methods should be moved to the top of their respective stacks. Delegation is enabled by default when GSSAPI authentication is selected.

Two-step Authentication

You can avoid some of the inconvenience of two-step authentication using ssh multiplexing. This feature creates a master session on initial connection to a particular host; subsequent sessions reuse the existing connection as a tunnel, so no further authentication is required. The master session can be configured to remain open even after you have closed the initial connection using the ControlPersist option. On macOS and Linux systems you can add the following lines to ~/.ssh/config file on your local system to enable multiplexing.

ControlMaster auto
ControlPath ~/.ssh/%r@%h:%p
ControlPersist yes

Note that while PuTTY and SecureCRT support multiplexing, they do not support ControlPersist, so the feature is of less utility for this purpose on Windows systems.

If you'd like to learn more, the OpenSSH Cookbook has a good introduction to multiplexing.

Keep-alive

A connection that is left open but idle might be closed after some time. Many SSH clients have a keep-alive feature that can be used to prevent idle disconnections.

OpenSSH

Add the following line to ~/.ssh/config on your local system.

ServerAliveInterval 60

PuTTY

Select ConnectionSending of null packets to keep session activeSeconds between keepalives (0 to turn off) 60 and ConnectionLow-level TCP connection optionsEnable TCP keepalives (SO_KEEPALIVE option).

SecureCRT

In the Session Options dialog, select TerminalAnti-idleSend protocol NO-OP every 60 seconds.

Mosh

Mosh is also supported for interactive terminal sessions. Mosh connections are more responsive under high-latency conditions, and can persist when your network changes or while your computer sleeps. The native Mosh client is available on macOS and Linux; on Windows you can use MobaXterm or the Mosh extension for Chrome.

Suggested OpenSSH Configuration

The options described above are here collected into a configuration that should be safe and convenient for most users connecting from macOS and Linux systems.

# ~/.ssh/config

IgnoreUnknown GSSAPIKeyExchange

# FarmShare 2

Host rice rice?? cardinal cardinal?
  HostName %h.stanford.edu

Host rice rice.stanford.edu rice?? rice??.stanford.edu cardinal cardinal.stanford.edu cardinal? cardinal?.stanford.edu
  ControlMaster auto
  ControlPersist yes
  GSSAPIDelegateCredentials yes

# All hosts

Host *
  ControlPath ~/.ssh/%r@%h:%p
  GSSAPIKeyExchange yes
  GSSAPIAuthentication yes
  ServerAliveInterval 60
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