3

I'm having an issue with establishing an ssh tunnel through a bastion host.

Having looked through various SE questions which potentially solve the problem, nothing has.

My ssh config file (local)

Host www
    HostName ***
    IdentityFile ~/.ssh/key.pem
    ProxyCommand ssh root@bastion -W %h:%p

Host bastion
    HostName ***
    IdentityFile ~/.ssh/key.pem
    StrictHostKeyChecking      no
    ProxyCommand               none
    ForwardAgent               yes

I have added the necessary config options on the bastion server (/etc/ssh/sshd_config):

PermitTunnel yes
AllowTCPForwarding yes
PermitOpen any
TCPKeepAlive yes

But I get the following error:

OpenSSH_7.2p2 Ubuntu-4ubuntu2.4, OpenSSL 1.0.2g  1 Mar 2016
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: /etc/ssh/ssh_config line 59: Applying options for www
debug1: Executing proxy command: exec ssh root@bastion -W ****:22
debug1: permanently_set_uid: 0/0
debug1: permanently_drop_suid: 0
debug1: key_load_public: No such file or directory
debug1: identity file ~/.ssh/key.pem type -1
debug1: key_load_public: No such file or directory
debug1: identity file ~/.ssh/key.pem-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.2p2 Ubuntu-4ubuntu2.4
channel 0: open failed: administratively prohibited: open failed
stdio forwarding failed
ssh_exchange_identification: Connection closed by remote host

There is one caveat with this setup in that the target host (www) is in an AWS VPC and is only addressable from the bastion. My assumption is that this shouldn't be an issue since the routing is done from the bastion but that's my last thought as being the issue in this scenario.

1

That's rather annoying. It turns out the the AWS AMI disables port forwarding in it's authorised_keys! That was a tricky one to debug when everything in the sshd config looks correct.

~/.ssh/authorized_keys

no-port-forwarding,no-agent-forwarding,no-X11-forwarding
  • 2
    The error you were looking for was the administratively prohibited: open failed in your ssh -vv output. – Zoredache Mar 23 '18 at 23:22

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