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I have two computers, both running Arch Linux. My desktop is running headless, constantly plugged into the ethernet jack in my room. My university has a campus-wide wifi network that I can use with my laptop. My problem arises when I try to ssh between the two. If both computers are plugged into ethernet jacks, there is no problem. But if the laptop is on wifi, neither one can ssh to the other.

The IP address of the desktop is (not actual IP; I changed the last byte) 130.18.119.210/22, and the laptop's wifi IP is 130.18.245.167/24 (again, last byte changed). I know the netmasks have something to do with this, but I'm not entirely sure what, as networking is one of the only things about computers that I'm not good at. What is the issue, and what might I be able to do to fix it?

When, from the laptop, I ping 130.18.119.210 the pings return successfully. But a traceroute 130.18.119.210 returns:

traceroute to 130.18.119.210 (130.18.119.210), 30 hops max, 60 byte packets
 1  130.18.67.1 (130.18.67.1)  7.460 ms  50.628 ms  57.059 ms
 2  core.cisco1.butler.mgmt.msstate.edu (130.18.0.11)  57.259 ms  57.537 ms  64.118 ms
 3  * * *
 4  * * *
 5  * * *
 6  * * *
 7  * * *
 8  * * *
 9  * * *
10  * * *
11  * * *
12  * * *
13  * *^C

Keep in mind that I don't have root to any infrastructure, just to my two machines. Thanks for any insight!

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1  
Nothing suggests any kind of configuration or networking problem. Almost certainly you either have a firewall on one of your machines that's blocking this or campus policy blocks it. –  David Schwartz Jan 10 '13 at 1:07
    
It looks to me that the wifi network block is separate from the wired connection network block. In any case scenario, your schools net admins wouldn't want wifi users to be in the same brodcast range as the wired connection because that would lead to security issue. So, its unlikely that you will be able to access ssh from you laptop if you don't have access to net filters ..etc. If you're trying to share files between ur pc's, I suggest you use different service from the web or directly connect you wired connection to a wifi-enabled router so you can become the admin to ur dorm/room –  WeloSefer Jan 10 '13 at 9:49
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1 Answer

up vote 1 down vote accepted
 130.18.116.210/22:  
 10000010 00010010 01110111 11010010      IP in binary
 11111111 11111111 11111100 00000000      Netmask for /22
 -----------------------------------
 10000010 00010010 01110100 00000000      Network part
 130      18        116            


 Laptop's wifi IP is 130.18.245.167/24
 Network 130.18.245.0

I see no problem with netmasks. Both computers are on different networks.

If both have a valid route to the outside world and there are no firewalls anywhere blocking access then they simply should be able to communicate.

That communication would not go direct from laptop to desktop, but via a longer route. Possibly running into some campus wide policies or firewalls. You can test this by trying to connect to either laptop or desktop from a third location and seeing if it works, or where it gets stopped.

Tools such as traceroute, ping, mtr etc come in handy.

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Hmmm. I updated my question with pings and traceroutes. Would you mind explaining the meanings of them? Also, I got the third byte of the desktop's IP wrong; it was 116 but is now 119. I think your binary diagram used 119 anyway. Thank you! –  thirtythreeforty Jan 10 '13 at 1:01
    
130.18.116.210/22 starts at 130.18.116.0 and end at 130.18.119.255. Thus you can get 116, 117, 118 and 119 in the third byte, depending on which IP your computer got. (And all thee are on the same /22 subnet). This URL might help explain that part: serverfault.com/questions/49765/how-does-ipv4-subnetting-work –  Hennes Jan 10 '13 at 1:23
    
As for explaining ping. It sends an ICMP echo request. That arrives, get parsed and send back. TIme between those is measured. The time is not important atm, what is important is that it gets back and that communication between the two machines is possible. If other forms do not work then those are either not enabled, blocked at your computers, or -most likely- blocked somewhere in between. The way around this are 1) Ask campus IT for an exception. 2) Hack around it with tunnels or a VPN, and depending on the rules maybe you get kicked of the campus net. Not recommended. –  Hennes Jan 10 '13 at 1:27
    
I see. Thank you for the link. I think there is likely a blockage somewhere in the university's infrastructure. –  thirtythreeforty Jan 10 '13 at 1:31
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