SSH Access Infrastructure SOP¶
SSH Agent forwarding
#fedora-admin or email@example.com
All IAD2 and VPN Fedora machines
Access via ssh to Fedora project machines.
This page will contain some useful instructions about how you can safely login into Fedora PHX2 machines successfully using a public key authentication. As of 2011-05-27, all machines require a SSH key to access. Password authentication will no longer work. Note that this SOP has nothing to do with actually gaining access to specific machines. For that you MUST be in the correct group for shell access to that machine. This SOP simply describes the process once you do have valid and appropriate shell access to a machine.
First of all: (on your local machine):
This file, and any keys, need to be chmod 600, or you will get a “Bad owner or permissions” error. The .ssh directory must be mode 700.
then, add the following:
Host bastion-iad01.fedoraproject.org User FAS_USERNAME ProxyCommand none ForwardAgent no Host *.iad2.fedoraproject.org *.qa.fedoraproject.org 10.3.160.* 10.3.161.* 10.3.163.* 10.3.165.* 10.3.167.* *.vpn.fedoraproject.org batcave01 User FAS_USERNAME ProxyCommand ssh -W %h:%p bastion-iad01.fedoraproject.org
How ProxyCommand works?
A connection is established to the bastion host:
+-------+ +--------------+ | you | ---ssh---> | bastion host | +-------+ +--------------+
Bastion host establish a connction to the target server:
+--------------+ +--------+ | bastion host | -------> | server | +--------------+ +--------+
Your client then connects through the Bastion and reaches the target server:
+-----+ +--------------+ +--------+ | you | | bastion host | | server | | | ===ssh=over=bastion============================> | | +-----+ +--------------+ +--------+
PuTTY SSH configuration¶
You can configure Putty the same way by doing this:
In the session section type batcave01.fedoraproject.org port 22
In Connection:Data enter your FAS_USERNAME
In Connection:Proxy add the proxy settings
ProxyHostname is bastion-iad01.fedoraproject.org
Proxy Command plink %user@%proxyhost %host:%port
In Connection:SSH:Auth remember to insert the same key file for authentication you have used on FAS profile
SSH Agent forwarding¶
You should normally have:
For Fedora hosts (this is the default in OpenSSH). You can override this on a per-session basis by using ‘-A’ with ssh. SSH agents could be misused if you connect to a compromised host with forwarding on (the attacker can use your agent to authenticate them to anything you have access to as long as you are logged in). Additionally, if you do need SSH agent forwarding (say for copying files between machines), you should remember to logout as soon as you are done to not leave your agent exposed.
‘channel 0: open failed: administratively prohibited: open failed’
If you receive this message for a machine proxied through bastion, then bastion was unable to connect to the host. This most likely means that tried to SSH to a nonexistent machine. You can debug this by trying to connect to that machine from bastion.
- if your local username is different from the one registered in FAS,
please remember to set up a User variable (like above) where you specify your FAS username. If that’s missing SSH will try to login by using your local username, thus it will fail.
- ssh -vv is very handy for debugging what sections are matching and
what are not.
- If you get access denied several times in a row, please consult with
#fedora-admin. If you try too many times with an invalid config your IP could be added to denyhosts.
- If you are running an OpenSSH version less than 5.4, then the -W
option is not available. In that case, use the following ProxyCommand line instead:
ProxyCommand ssh -q bastion.fedoraproject.org exec nc %h %p