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#1 2012-12-15 11:44:39

zilti
Member
Registered: 2012-11-11
Posts: 13

Unable to connect to a computer in the local network

I've set up an older notebook as a server, connected via WiFi, will be called "server" in this text. Then I have my normal work notebook, called "notebook" in this text.
Both the server and the notebook are connected to the router. The server has additionally a no-ip.org domain.
server ip: 192.168.1.14, notebook ip: 192.168.1.15, router ip: 192.168.1.1
Now just after rebooting and after resetting the wifi connection, I can ping and ssh the server from the notebook.
After some time though something strange happens...
I can't connect to the server from my notebook, neither through the mDNS address nor through 192.168.1.14, all I get is "ssh: connect to host 192.168.1.14 port 22: No route to host".
But if I ssh to the server from my notebook via the no-ip.org domain, it works perfect.
I can then ping 192.168.1.1 from both the server and the notebook, but I can neither ping 192.168.1.15 from the server nor 192.168.1.14 from the notebook...
They lose each others ARP entries, too.
What might the reason for this strange behaviour be?
Where's the problem? SSH config? Server config? Router config?

What I tried until now:
- Letting the server regularly restart its network connection - it seems to help sometimes, but not "forever". Additionally it's a terrible solution.

- Letting the server regularly restart avahi-daemon: Oddly enough using that both servers have each others mDNS and MAC-Addresses all the time, but still aren't able to connect.

-Letting the server regularly ping the router: Well, that didn't help either. That just works anyway.

Last edited by zilti (2012-12-15 11:45:01)

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#2 2012-12-15 12:05:28

Pajaro
Member
Registered: 2004-04-21
Posts: 878

Re: Unable to connect to a computer in the local network

It looks that your are you using ap isolation in your wifi access point.

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#3 2012-12-15 12:37:13

zilti
Member
Registered: 2012-11-11
Posts: 13

Re: Unable to connect to a computer in the local network

No, that definitely isn't the case. If it were, I couldn't ever establish a connection.

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#4 2012-12-15 13:11:36

satanselbow
Member
Registered: 2011-06-15
Posts: 532

Re: Unable to connect to a computer in the local network

You can either post your config files as they stand - so we can have a look and suggest a sane solution... or you can keep changing random stuff and generating more breakage... your choice wink Have you a firewall running somewhere that is closing a port? More food (or confusion) for the mix wink

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#5 2012-12-15 15:17:54

zilti
Member
Registered: 2012-11-11
Posts: 13

Re: Unable to connect to a computer in the local network

Ok. The only firewall is the one on my router, so I don't have one at my two laptops.
Both laptops connect via WiFi using wicd. Which config files are important?
Here's my /etc/nsswitch.conf:

# Begin /etc/nsswitch.conf

passwd: files
group: files
shadow: files

publickey: files

hosts: files myhostname mdns4_minimal [NOTFOUND=return]  dns mdns4
#hosts: files mdns4 dns
networks: files

protocols: files
services: files
ethers: files
rpc: files

netgroup: files

EDIT: What I forgot to mention: If I make the ARP entry permanent, I can always connect without any problem (At least at the day I tested that). But that can't be the solution.

Last edited by zilti (2012-12-15 15:28:53)

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#6 2012-12-24 15:47:19

zilti
Member
Registered: 2012-11-11
Posts: 13

Re: Unable to connect to a computer in the local network

Now what's completely strange is that it's perfectly possible to connect to the server from a windows notebook where it is set up as ipp printer, and perfectly possible to connect via the no-ip.org domain, but not from my linux-notebook or my android phone.

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#7 2012-12-24 16:57:06

ewaller
Administrator
From: Pasadena, CA
Registered: 2009-07-13
Posts: 12,965

Re: Unable to connect to a computer in the local network

Tell us more about the router.
Do you have access to it's logs?
Are you using static or dynamic addresses?
Can you post the output of ip addr and of ip route from the notebook when things are not working?


Nothing is too wonderful to be true, if it be consistent with the laws of nature -- Michael Faraday
Like you, I have no idea what you are doing, but I am pretty sure it is wrong...Jasonwryan
----
How to Ask Questions the Smart Way

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#8 2012-12-24 17:02:49

zilti
Member
Registered: 2012-11-11
Posts: 13

Re: Unable to connect to a computer in the local network

The router is a Zyxel NBG-419N. I have access to logs, but I don't think they're too useful.
I'm using DHCP, but have MAC-to-IP-mappings.
ip addr:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 08:ed:b9:5b:aa:83 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.15/24 brd 192.168.1.255 scope global wlan0
    inet6 fe80::aed:b9ff:fe5b:aa83/64 scope link 
       valid_lft forever preferred_lft forever

ip route

default via 192.168.1.1 dev wlan0  metric 303 
192.168.1.0/24 dev wlan0  proto kernel  scope link  src 192.168.1.15  metric 303

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#9 2012-12-24 17:18:47

ewaller
Administrator
From: Pasadena, CA
Registered: 2009-07-13
Posts: 12,965

Re: Unable to connect to a computer in the local network

Well, that all looks rational.
I would check the router status at the time of difficulty and see if it thinks all the systems are connected.  This just smells like a routing problem in the router.

Any chance you have set up a DMZ containing either the server or the notebook?

Also, maybe I missed it, but, when you are having the problem, can both systems still access the Internet?  You kind of implied it when you said you could hit the server though no-ip.org -- if one assumes you hit that domain starting from your private network.  Alternately, it is possible you hit it from an external network (using a cell phone, for example)

Last edited by ewaller (2012-12-24 17:19:17)


Nothing is too wonderful to be true, if it be consistent with the laws of nature -- Michael Faraday
Like you, I have no idea what you are doing, but I am pretty sure it is wrong...Jasonwryan
----
How to Ask Questions the Smart Way

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#10 2012-12-24 23:40:13

zilti
Member
Registered: 2012-11-11
Posts: 13

Re: Unable to connect to a computer in the local network

No, there's no DMZ defined for any of the computers.
Both/all systems have access to the Internet the whole time. I somehow suspect that mDNS might play a role here (even when directly using the IP address), since Windows doesn't support mDNS.
no-ip.org access happens from my network over no-ip.org back to my network, and strange enough when I last tested it I had a lower ping via no-ip.org than via direct IP.

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