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Link 2 computers by wifi with httpd allows only one way trafic

Link to this post 04 Apr 12

Hello all.

I have a small problem, I'm trying to connect two computers directly creating in one of them an AP using hostapd.
I more or less followed this: https://www.linux.com/learn/tutorials/442417-create-a-secure-linux-based-wireless-access-point

I've managed to create my AP without trouble and connected my other computer to it, but they cannot ping each other.
At first I thought it was a problem assigning IP's, so I decided to use static IP so I don't have to use a dhcp sever.

My client is 192.168.128.100 with netmask 255.255.255.0 and my AP is 192.168.128.1 with the same netmask.
I configurated them using

ifconfig wlan0 129.168.127.XXX netmask 255.255.255.0

So I tcpdumped both connections to see what was going on and ping'ed.
If I ping from my AP to the other computer:
ping -I wlan0 192.168.128.100

I get this in my AP's tcpdump (using tdpdump -i wlan0):
ARP, Request who-has 192.168.128.100 tell 192.168.128.1, length 28

Nothing else, no reply nor anything.

But, in my client's tcpdump I get:

ARP, Request who-has 192.168.128.100  tell 192.168.128.1, length 28
ARP, Reply 192.168.128.100 is-at XX:XX:XX:XX:XX:XX (oui Unknown), length 28

So my AP is not receiving the reply but my client receives the ping request.

If I do it the other way (Ping from the client to the AP) the client tcpdump shows that it is trying to send the ARP request, but the AP does not log anything at all.

I'm confused. I don't really know much about networking but I feel that something odd happens here. For example, the AP does receive some data because I can connect both computers and hostapd shows that the authentication is correct.

My AP is OpenSuse 11.4 and the client right now is BackTrack linux, but later I plan to use a debian and a windows computer as clients.
Also, I've been using linux for a long time, but with my wifi I've always used some kind of GUI like kdenetworkmanager so I don't really know how to do everything properly with the console, and maybe I'm skipping something important.
I stopped my firewall in the AP just in case.

Thank you very much in advance!

Link to this post 06 Apr 12

Hello nake,

I was just reading the tutorial you linked to. The information is very technical. From what you posted, it looks like your Wifi-card has a static address(wlan0 129.168.127.XXX) which is not in the same network as your AP(192.168.128.1). Could you run "ifconfig" on both systems and post the output of the command?

Link to this post 08 Apr 12

I saw the same simple issue, looks like a simple typo, but could also be your problem. Let us know =)

Link to this post 11 Apr 12

I'm not sure if I did that typo while posting it here or it was in the computers I was trying to connect. However I'm on holidays this week so I wont be able to try it now.

Thanks for the fast answer though! As soon as I try it I'll post it here.

Link to this post 17 Apr 12

Nope, the problem persists.

I'm starting to think it might be some kind of problem with the packet's routing over the kernel.
I started a dhcpd daemon just to make sure I was not screwing some kind of ip assignment, my config looks like this:


option routers 192.168.128.1;
option subnet-mask 255.255.255.0;
option broadcast-address 192.168.128.255;
option netbios-name-servers 192.168.128.1;

default-lease-time 86400;
max-lease-time 86400;

authoritative;


subnet 192.168.128.0 netmask 255.255.255.0 {
range 192.168.128.100 192.168.128.200;
}

I started the daemon with dhcpd wlan0 (and the leases file exists). No errors seem to show up.

Then, in my client (linked with wpa_supplicant) I run dhclient wlan0 and it tries to send messages but none of them arrive to my ap. I saw in tcpdump that it sends packets to 255.255.255.255 but they get not logged in my ap's tcdump... In the end it said that no DHCPOFFERS where received.
Also, as I said, if I ping from the AP to the client ping requests do arrive, but the reply from the client to the AP does not arrive to the AP. That's why I'm starting to think that the problem is that my ap is rejecting or dropping packets.

I don't know how to check if that's my problem. As my AP is opensuse I rechecked in yast that my firewall is disabled, but as far as I know there could be other kind of firewalls like iptables and configuration files to reject connections and packets, but I don't know how to check and change those. Any ideas?

If I can I'll try to do the same with another computer as AP to see if the problem is a misconfiguration somewhere.

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