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5:02 PM
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Q: Can't SSH into a PC

Nikola PantelicI have a laptop with Linux Mint and Windows 10. I can SSH into both Windows and Linux from both my Windows and Linux systems, but neither Linux nor Windows can SSH into this PC, no matter what OS is in the current use. This OS can't be pinged too (no matter what OS sends pings, and no matter wha...

linux windows networking ssh
 
Gerard H. Pille
Gerard H. Pille
What does your LAN look like?
 
Nikola Pantelic
Nikola Pantelic
C type IP, star topology, with 5-10 devices connected to it. Other PCs on this network work normally (no matter the OS), the problematic is only one laptop.
 
Gerard H. Pille
Gerard H. Pille
"C type IP, star topology" is this some kind of device?
 
Nikola Pantelic
Nikola Pantelic
Yes, this is an Asus laptop. Those descriptions refer to the network itself.
 
Gerard H. Pille
Gerard H. Pille
I'll try it another way: how are the systems connected to each other?
 
Nikola Pantelic
Nikola Pantelic
5:02 PM
Phones and laptops through Wi-Fi, desktop computers with UTP cables. They are all connected to the (and only to the) central switch/router.
 
Gerard H. Pille
Gerard H. Pille
Can you identify the switch? Is the switch providing DHCP? Do ALL connected devices use DHCP?
 
Nikola Pantelic
Nikola Pantelic
With nmap? Yes.
 
Gerard H. Pille
Gerard H. Pille
No, I want to know the brand and model of the switch.
 
Nikola Pantelic
Nikola Pantelic
Is this it: ZXHN H168N V3.1? Also, it says ZTE on the label.
All devices use DHCP, and I have no problem with it.
 
Gerard H. Pille
Gerard H. Pille
Finally. I'm checking the manual. Can you verify the DHCP, no duplicate IP addresses?
So, maximum four devices through UTP? The ZXHN has a firewall that provides "local security". No luck with the manual so far, it's in Tsjech
 
Nikola Pantelic
Nikola Pantelic
5:02 PM
There are no duplicate addresses.
I couldn't find that option in settings.
 
Gerard H. Pille
Gerard H. Pille
What is the IP address of the system you cannot reach, and an IP address of a system you can reach?
 
Nikola Pantelic
Nikola Pantelic
I can't reach 192.168.1.6, I can reach 192.168.1.5.
 
Gerard H. Pille
Gerard H. Pille
There is no firewall configured on the 192.168.1.6 itself? What is the route configuration on the system that tries to connect to the 192.168.1.6? I'd like to see "netstat -rn".
 
Nikola Pantelic
Nikola Pantelic
What is the Linux equivalent of that command? I can't use any machine with Windows right now.
 
Gerard H. Pille
Gerard H. Pille
I would never issue a Windows command. netstat exists on Linux. route is good too. You may need to be root. "route -n"
Also, from the system you can't reach, you do an ssh to another system, and there you execute "who". It should show the IP address you come from.
 
Nikola Pantelic
Nikola Pantelic
5:02 PM
who in SSH does return the correct IP address.
 
Gerard H. Pille
Gerard H. Pille
I'm grasping at straws. Can you try to restart the ZTE?
 
Nikola Pantelic
Nikola Pantelic
Already tried that.
If it matters, I can detect that PC with command nmap -sL 192.168.1.0/24. nmap -sn 192.168.1.0/24 is the one that can't detect it.
 
Gerard H. Pille
Gerard H. Pille
nmap manual says -sL is not really a scan. When you run "arp" on one of the other systems, do you see the 192.168.1.6? Is its mac address correct?
If the ARP table is correct, there's only this left: On the main page of the ZXHN H168N, select Internet > Security > Firewall Check all the rules if you find anything concerning 192.168.1.6.
 
Nikola Pantelic
Nikola Pantelic
arp shows no output.
I only have Port Forwarding: imgur.com/a/GYPv6.
 
Gerard H. Pille
Gerard H. Pille
arp should at least show the 192.168.1.1, your gateway / switch ?? You can ping the 192.168.1.1, can't you?
 
Nikola Pantelic
Nikola Pantelic
5:02 PM
It's completely empty.
 
Gerard H. Pille
Gerard H. Pille
On the ZTE status page, can you see the devices connected via WiFi?
 
Nikola Pantelic
Nikola Pantelic
Yes. Via Ethernet too.
 
Gerard H. Pille
Gerard H. Pille
And the 192.168.1.6 is there?
 
Nikola Pantelic
Nikola Pantelic
Yes. Also, arp for some reason now does show my gateway.
Looks like my NIC needs first to communicate with the gateway to be able to get some information. When I run arp a moment ago, I just booted the system. But if I first go to or ping some website, arp does detect my gateway.
 
Gerard H. Pille
Gerard H. Pille
OK, but that is normal for arp. Could it be that the wifi on the 192.168.1.6 goes to sleep if it's not in use?
 
Nikola Pantelic
Nikola Pantelic
5:02 PM
Hardly. Only if it goes to sleep for 10s of non-use, because many times I was using the PC at the same time I tried to SSH into it/ping it/detect it.
 
Gerard H. Pille
Gerard H. Pille
Have you verified the arp after pinging the 192.168.1.6 from another system
 
Nikola Pantelic
Nikola Pantelic
5:29 PM
After pinging 192.168.1.6, arp shows an entry with 192.168.1.6 with correct hostname but incorrect MAC address (only one hexbit is wrong).
 

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