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Author Topic: Attempting to Connect an iPad to a Remote R-Pi via SSH  (Read 328 times)

Weaver

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Attempting to Connect an iPad to a Remote R-Pi via SSH
« on: September 07, 2018, 07:59:23 AM »

I am trying to get my iPad to connect to a remote, hosted raspberry Pi by using SSH. The iPad is running the Prompt2 IRC client. No joy on this iPad, but I have got everything working ok on a different iPad. The Pi is running Ubuntu 16.04. I can try using a username and password or using PKI. I have both options working on the other iPad: PKI with Prompt2 and remote file system access over SSH using a deifferent iPad app (Textastic).

I did a traffic capture over the link to the internet. If not using PKI, just username root, password whatever and port 5069 then I get a TCP CONNECT (SYN) going out, then TCP CONNECT_ACK (SYN|ACK) coming back, then nothing.

If I try the same but select using PKI instead of the ordinary username and password I get the same CONNECT and response CONNECT_ACK, but then an inbound CONNECT request from an alias address and of course this gets thrown away by firewalling.

Any clues?
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burakkucat

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Re: Attempting to Connect an iPad to a Remote R-Pi via SSH
« Reply #1 on: September 07, 2018, 05:40:29 PM »

[Moderator note: Adjusted the subject line.]

Do you have any clue as to where the process is "falling over"? I am uncertain if it is the software configuration on the iPad or on the R-Pi.
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Weaver

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Re: Attempting to Connect an iPad to a Remote R-Pi via SSH
« Reply #2 on: September 07, 2018, 05:56:17 PM »

I can't see his it can be a problem with the Pi because that is unchanged between the two situations where it is working with the one iPad and failing with the other one.

A thought. Is there any possible problem with having two SSH sessions in progress at the same time? I am suddenly wondering if the second iPad is just unlucky because it is coming late to the party - its only crime is that if being second. Can soon sort out that question by rebooting the Pi and simply trying a login from the second iPad.
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tickmike

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Re: Attempting to Connect an iPad to a Remote R-Pi via SSH
« Reply #3 on: September 08, 2018, 02:42:40 PM »

Firewall blocking it ?.
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Weaver

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Re: Attempting to Connect an iPad to a Remote R-Pi via SSH
« Reply #4 on: September 09, 2018, 10:23:40 PM »

No software firewall at either end. The router at this end has the usual state full firewall and is common to both situations, the one where there is an iPad 5 successfully connecting to the Pi and the one where the iPad Pro just sits there. If the Pi were trying to make a reverse TCP connection back to the iPad then this would certainly stop things working, but why then is the iPad 5 working?

I have reinstalled the SSH client app on the iPad Pro and tried again, but no luck.
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andyfitter

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Re: Attempting to Connect an iPad to a Remote R-Pi via SSH
« Reply #5 on: September 09, 2018, 11:42:38 PM »

One iPad on 2.4ghz and one on 5ghz, and something in between treating them differently?
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Weaver

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Re: Attempting to Connect an iPad to a Remote R-Pi via SSH
« Reply #6 on: September 10, 2018, 12:19:49 AM »

The two iPads are on the same SSID and that particular one happens to be 5GHz only. All SSIDs go to the same one and only switch and firewall-router to the Remote raspberry Pi which is off-site. Some SSIDs have different security settings, for example the guest SSID has inter-station isolation and an L2 isolation firewall that only permits access to the router and nothing else so that the guest clients have access to the internet but that is all, no access to other wired-LAN boxes. But none of that is effective here.

The iPad Pro (which doesnít work) is at least trying to do something as a packet cap true proves: it sends out a TCP CONNECT to port 5069 over IPv6 and a TCP CONNECT_ACK comes back. I have tried SSH with username and password, with a bad username and with PKI instead of a password. The working iPad 5 does the PKI login method, and a different app on that machine successfully does the username+password method.

I should do another packet capture on the iPad 5 (working) case, to see what success looks like.
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Weaver

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Re: Attempting to Connect an iPad to a Remote R-Pi via SSH
« Reply #7 on: September 12, 2018, 04:29:35 AM »

I have tried two other IRC clients on the iPad Pro, exactly the same bad result.

It is as if the Pi either has developed some stateful association with the first iPad, the iPad 5, maybe by source address, or else it just does not like having two simultaneous SSH connections. mind you, in the second case, I donít know why the first connection would not have timed out possibly, but you could get locked out forever like that, just because you change IP address, which happens a lot, especially with IPv6, and of course with mobile machines, machines that are multihimed, or roam to 4G or umpteen other things?
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